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WO2025053187A1 - Diode verticale et procédé de fabrication de diode verticale - Google Patents

Diode verticale et procédé de fabrication de diode verticale Download PDF

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Publication number
WO2025053187A1
WO2025053187A1 PCT/JP2024/031773 JP2024031773W WO2025053187A1 WO 2025053187 A1 WO2025053187 A1 WO 2025053187A1 JP 2024031773 W JP2024031773 W JP 2024031773W WO 2025053187 A1 WO2025053187 A1 WO 2025053187A1
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Prior art keywords
electrode
organic semiconductor
semiconductor layer
vertical diode
weight hydrophobic
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Japanese (ja)
Inventor
龍幸 牧田
侑 山下
純一 竹谷
峻一郎 渡邉
永祥 刑部
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PI-CRYSTAL Inc
National Institute for Materials Science
University of Tokyo NUC
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PI-CRYSTAL Inc
National Institute for Materials Science
University of Tokyo NUC
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D8/00—Diodes
    • H10D8/01—Manufacture or treatment
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D8/00—Diodes
    • H10D8/50—PIN diodes 
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K10/00—Organic devices specially adapted for rectifying, amplifying, oscillating or switching; Organic capacitors or resistors having potential barriers
    • H10K10/20—Organic diodes

Definitions

  • This disclosure relates to a vertical diode and a method for manufacturing a vertical diode.
  • Non-Patent Document 1 discloses a method for adjusting the work function of an electrode by coating the electrode with a polymer material such as polyethyleneimine.
  • Non-Patent Document 2 discloses a method for adjusting the work function of an electrode by forming a thin film on the electrode using a material such as a polymer electrolyte and a tertiary aliphatic amine.
  • a diode is a device that has rectification characteristics in which a current flows only in the forward direction and is difficult to flow in the reverse direction.
  • diodes obtained by modifying the electrode surface by the methods described in Non-Patent Documents 1 and 2 may not have sufficient rectification characteristics, and improvement is desired.
  • An object of the present disclosure is to provide a vertical diode having excellent rectification characteristics.
  • the inventors have conducted extensive research. As a result, they have found that a vertical diode with excellent rectification characteristics can be obtained by using an electrode whose surface is modified with hydrophobic closed-shell ions. They have also found that a vertical diode with excellent rectification characteristics can be obtained by injecting carrier and dopant ions into an organic semiconductor in the vicinity of the electrode.
  • the gist of the present disclosure is as follows.
  • the low-molecular-weight hydrophobic ion is a low-molecular-weight hydrophobic closed-shell ion.
  • the low molecular weight hydrophobic ion is a low molecular weight hydrophobic cation
  • the low molecular weight hydrophobic ion is a low molecular weight hydrophobic anion
  • each R 14 is independently a hydrogen atom, a halogen atom, or a fluorinated alkyl group which may have a substituent
  • each R 15 is independently a perfluoroalkyl group, and two R 15s may be bonded to each other to form a ring.
  • the small molecule hydrophobic ions form an ion layer on a surface of the first electrode adjacent to the organic semiconductor layer;
  • the vertical diode according to any one of [1] to [5], wherein the thickness of the ion layer is 2 nm or less or a thickness of three molecular layers or less.
  • a ratio of the low-molecular-weight hydrophobic ions forming a salt with a counter ion among the low-molecular-weight hydrophobic ions attached to a surface of the first electrode that is adjacent to the organic semiconductor layer is 25 mol % or less;
  • the first electrode is a copper electrode.
  • the low molecular weight hydrophobic ion is a low molecular weight hydrophobic cation
  • the organic semiconductor layer has a doped layer and an undoped layer
  • the vertical diode according to any one of [1] to [3] and [5] to [8], wherein the doped layer is a layer adjacent to the second electrode and contains holes and dopant anions.
  • the low molecular weight hydrophobic ion is a low molecular weight hydrophobic anion
  • the organic semiconductor layer has a doped layer and an undoped layer
  • the vertical diode according to any one of [1] to [11] having a conversion efficiency from AC power at a frequency of 10 MHz to DC power of more than 5%.
  • the method for producing a vertical diode, wherein the surface modifying liquid is any one of the following surface modifying liquids (S1) to (S4): (S1) a surface modifying liquid containing a first reducing agent that reduces the first electrode and generates a low-molecular-weight hydrophobic cation; (S2) a surface modifying liquid containing a
  • the organic semiconductor layer has a doped layer and an undoped layer, the doped layer being adjacent to the second electrode; a doping step of contacting a surface of an organic semiconductor layer precursor with an aqueous solution containing one or more selected from the group consisting of a third oxidizing agent and a third reducing agent and a salt of a dopant ion, thereby forming the doped layer; a lamination step of laminating the organic semiconductor layer and the second electrode such that the doped layer and the second electrode are in contact with each other;
  • a surface modification liquid for modifying a surface of an electrode and changing a work function of the electrode comprising:
  • the surface modifying liquid is any one of the following surface modifying liquids (S1) to (S4).
  • S1 A surface modification liquid containing a first reducing agent that reduces the electrode and generates a low-molecular-weight hydrophobic cation.
  • S2 a surface modifying solution containing a first oxidizing agent that oxidizes the electrode and generates a low-molecular-weight hydrophobic anion.
  • S3 A surface modification solution containing a second reducing agent that reduces the electrode and a low-molecular-weight hydrophobic closed-shell cation.
  • (S4) A surface modification solution containing a second oxidizing agent that oxidizes the electrode and a low-molecular-weight hydrophobic closed-shell anion.
  • the surface modifying liquid according to [22] wherein the surface modifying liquid (S2) further contains a low-molecular-weight hydrophobic anion different from the low-molecular-weight hydrophobic anion generated from the first oxidizing agent.
  • a vertical diode including a first electrode, an organic semiconductor layer having a doped layer and an undoped layer, and a second electrode stacked adjacent to each other in this order, with the doped layer being adjacent to the first electrode or the second electrode, the doped layer includes carriers and dopant ions;
  • the doped layer is adjacent to the second electrode, the carriers are holes, the dopant ion is a hydrophobic closed shell anion;
  • the vertical diode according to claim 28, wherein a low-molecular-weight hydrophobic closed-shell cation is attached to a surface of the first electrode that is adjacent to the organic semiconductor layer.
  • the doped layer is adjacent to the second electrode, the carriers are electrons, the dopant ion is a hydrophobic closed shell cation;
  • a ratio of the dopant ions forming a salt with a counter ion to the dopant ions contained in the doped layer is 25 mol % or less;
  • the fourth reducing agent is at least one selected from the group consisting of a hydroquinone compound having a hydroquinone skeleton and a reduced coenzyme, The method for producing a vertical diode according to [34], wherein the fourth oxidant is a quinone compound having a quinone skeleton.
  • the doped layer is adjacent to the second electrode, The method further includes an electrode modification step of modifying a surface of the first electrode by contacting the surface of the first electrode with a surface modification liquid, The method for producing a vertical diode according to [34] or [35], wherein the surface modifying liquid is any one of the following surface modifying liquids (S1) to (S4).
  • (S1) a surface modifying liquid containing a first reducing agent that reduces the first electrode and generates a low-molecular-weight hydrophobic cation;
  • (S2) a surface modifying liquid containing a first oxidizing agent that oxidizes the first electrode and generates a low-molecular-weight hydrophobic anion.
  • (S3) a surface modifying solution containing a second reducing agent that reduces the first electrode and a low-molecular-weight hydrophobic closed-shell cation.
  • (S4) a surface modifying solution containing a second oxidizing agent for oxidizing the first electrode and a low-molecular-weight hydrophobic closed-shell anion.
  • the present disclosure has the effect of providing a vertical diode with excellent rectification characteristics.
  • the problems and advantages of the present disclosure are not limited to those specifically described above, but include those that will become apparent to those skilled in the art from the entire specification.
  • FIG. 6 is a schematic cross-sectional view showing the structure of a vertical diode according to a second embodiment.
  • FIG. 13 is a schematic cross-sectional view showing the structure of a vertical diode according to a fourth embodiment.
  • FIG. 13 is a schematic diagram of a circuit used to evaluate 10% rectification at 1 GHz of the vertical diode prepared in Example 13.
  • FIG. 13 is a diagram showing the evaluation results of 10% rectification at 1 GHz of the vertical diode produced in Example 13.
  • FIG. 13 is a diagram showing the evaluation results of the conversion efficiency from AC power to DC power of the vertical diode fabricated in Example 6.
  • FIG. 2 is a diagram showing the current-voltage characteristics of the vertical diode fabricated in Example 1.
  • FIG. 1 shows the results of UPS measurement of the surface-modified Cu electrode prepared in Example 2.
  • FIG. 1 shows the results of UPS measurement of the unmodified Cu electrode prepared in Comparative Example 1.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode fabricated in Example 3.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode fabricated in Example 4.
  • FIG. 1 shows the results of UPS measurement of the surface-modified Cu electrode prepared in Example 2.
  • FIG. 1 shows the results of UPS measurement of the unmodified Cu electrode prepared in Comparative Example 1.
  • FIG. 13 is a diagram showing the current-voltage
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode fabricated in Example 5.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode fabricated in Example 6.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode fabricated in Example 7.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode produced in Comparative Example 2.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode produced in Comparative Example 3.
  • FIG. 13 is a diagram showing the results of PYS measurement of the surface-modified ITO electrode prepared in Example 8.
  • FIG. 13 is a diagram showing the PYS measurement results of the unmodified ITO electrode prepared in Comparative Example 3.
  • FIG. 13 is a diagram showing the PYS measurement results of the surface-modified ITO electrode prepared in Comparative Example 4.
  • FIG. 13 is a diagram showing the results of XPS elemental analysis of the unmodified ITO electrode prepared in Comparative Example 3.
  • FIG. 13 is a diagram showing the results of XPS elemental analysis of the surface-modified ITO electrode prepared in Example 9.
  • FIG. 13 is a diagram showing the results of XPS elemental analysis of the unmodified ITO electrode prepared in Comparative Example 5.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode prepared in Example 10.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode produced in Comparative Example 6.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode prepared in Example 11.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode prepared in Example 12.
  • FIG. 13 is a diagram showing the current-voltage characteristics of the vertical diode prepared in Example 13.
  • FIG. 13 is a diagram showing the evaluation results of the conversion efficiency from AC power to DC power of the vertical diode produced in Example 13.
  • FIG. 15 is a diagram showing the current-voltage characteristics of the vertical diode prepared in Example 14.
  • X to Y indicating a range means “X or more and Y or less.”
  • a numerical range represented by “X to Y” or “X or more and Y or less” is described in stages (for example, in order of preference), the upper and lower limits of each numerical range can be combined in any combination.
  • a description such as "X such as x1, x2, and x3" lists x1, x2, and x3 as examples of X, and does not mean that X is limited to x1, x2, x3, and the like.
  • a first embodiment of the present disclosure is a method for manufacturing a vertical diode in which a first electrode, an organic semiconductor layer, and a second electrode are stacked adjacent to each other in this order.
  • the manufacturing method according to this embodiment includes an electrode modification step of contacting a surface of a first electrode with a surface modification liquid to obtain a surface-modified first electrode; and a lamination step of laminating the first electrode and the organic semiconductor layer so that the surface of the first electrode modified in the electrode modification step comes into contact with the organic semiconductor layer.
  • the surface modification liquid used in the electrode modification step is any one of surface modification liquids (S1) to (S4).
  • S1 A surface modifying solution containing a first reducing agent that reduces a first electrode and produces low-molecular-weight hydrophobic cations.
  • S2 A surface modifying solution containing a first oxidizing agent that oxidizes the first electrode and generates a low-molecular-weight hydrophobic anion.
  • S3 A surface modification solution containing a second reducing agent that reduces the first electrode and a low-molecular-weight hydrophobic closed-shell cation.
  • S4 A surface modification solution containing a second oxidant that oxidizes the first electrode and a low-molecular-weight hydrophobic closed-shell anion.
  • hydrophobic means the property of having a low affinity for water and not dissolving or mixing in water, or being difficult to do so.
  • hydrophobic ions refers to ions that contain one or more hydrophobic sites.
  • hydrophobic sites include aromatic hydrocarbon groups having 5 to 20 carbon atoms, such as cyclopentadienyl groups and phenyl groups; aromatic heterocyclic groups having 3 to 20 carbon atoms, such as imidazolyl groups; hydrocarbon groups having 8 to 20 carbon atoms, such as octyl groups; fluorinated aliphatic hydrocarbon groups having 1 to 20 carbon atoms, such as trifluoromethyl and pentafluoroethyl groups, preferably perfluoroaliphatic hydrocarbon groups; and fluorinated aromatic hydrocarbon groups having 6 to 20 carbon atoms, such as pentafluorophenyl groups and heptafluoronaphthyl groups, preferably perfluoroaromatic hydrocarbon groups.
  • the number of hydrophobic sites per molecule of the hydrophobic ion is preferably 1 to 10, more preferably 1 to 8, even more preferably 2 to 6, and particularly preferably 2 to 4.
  • the ions become sufficiently bulky and exhibit hydrophobicity, resulting in a surface-modified electrode that is highly stable against water and air.
  • a surface-modifying liquid containing a sufficient concentration of hydrophobic ions can be prepared.
  • Hydrophobic ions are preferably ones in which the charge is widely delocalized within the hydrophobic ion. This is because the delocalization of the charge makes it possible to suppress local interactions with water, improving the hydrophobicity of the hydrophobic ion.
  • the hydrophobic ion In order to delocalize the charge over a wide range of the hydrophobic ion, it is preferable for the hydrophobic ion to have a conjugated structure, an electron-withdrawing group (if the hydrophobic ion is a hydrophobic anion), an electron-donating group (if the hydrophobic ion is a hydrophobic cation), or the like.
  • low molecular weight means that there is no molecular weight distribution and that the molecular weight is 2,000 or less, preferably 1,000 or less, more preferably 800 or less, and even more preferably 500 or less.
  • molecules or ions that have a molecular weight distribution and have a molecular weight of 1,000 or more are distinguished by being called “macromolecules” or “polymers”.
  • a vertical diode exhibiting excellent rectification characteristics can be obtained. Therefore, the manufacturing method according to this embodiment is useful as a method for manufacturing a rectifier diode.
  • a rectifier diode has a feature that the current value in the forward direction is higher than that in the reverse direction, and the rectification ratio, which is the ratio, is two digits or more, preferably three digits or more.
  • the degree of freedom in selecting the electrode material can be greatly improved.
  • a vertical diode having excellent high frequency response or a vertical diode exhibiting high current density even at a low voltage can be obtained.
  • current density means a forward current density.
  • high current density at a low voltage means that the forward current density at a forward voltage of 2V is 1 Acm -2 or more, preferably 10 Acm -2 or more, more preferably 100 Acm -2 or more.
  • the vertical diode obtained by the manufacturing method according to the present embodiment is considered to be applicable to various devices having a diode structure, such as solar cells and light-emitting diodes, and is also expected to be applied to electronic tags for wireless communication, which require high-frequency response.
  • the electrode modification step is a step of modifying the surface of the first electrode by bringing the surface of the first electrode into contact with any one of the surface modifying solutions (S1) to (S4).
  • the surface-modified first electrode is a first electrode on which low-molecular-weight hydrophobic ions are attached to the surface adjacent to the organic semiconductor layer when the vertical diode is fabricated.
  • the work function of the first electrode can be significantly shifted by a simple solution process in which the surface of the first electrode is brought into contact with a surface modification liquid.
  • the resulting electrode has low atmospheric stability, and when exposed to the atmosphere, the work function returns to approximately the same level as before the surface modification.
  • the electrode modification step in this embodiment makes it possible to obtain a surface-modified electrode that is highly water-resistant and atmospherically stable. Therefore, as shown in the examples described below, even when the work function is measured after exposing the surface-modified electrode to the atmosphere, the work function that was shifted shallowly or deeply in the electrode modification step is maintained.
  • the work function is the difference (positive value) between the Fermi level and the vacuum level.
  • the Fermi level is the energy level at which the probability of electron occupancy is 0.5.
  • the work function is equal to the ionization potential, which is the minimum energy required to extract one electron into a vacuum.
  • the work function can be measured using an ultraviolet photoelectron spectrometer.
  • the work function is a value measured using a photoelectron yield spectroscopy device for carrying out ionization potential measurement (for example, "AC-3" manufactured by Riken Keiki Co., Ltd.).
  • the surface modifying liquids (S1) to (S4) for modifying the surface of the first electrode are preferably solutions or dispersions, more preferably solutions.
  • the components contained in the surface modifying liquids (S1) to (S4) are described below.
  • the first reducing agent contained in the surface modifying liquid (S1) is a compound that reduces the first electrode and generates low molecular weight hydrophobic cations.
  • the surface modifying liquid (S1) is used as the surface modifying liquid, in this process, electrons are injected into the first electrode (i.e., the surface of the first electrode is reduced), thereby negatively charging the surface of the first electrode.
  • low molecular weight hydrophobic cations generated from the first reducing agent are electrostatically attached to the surface of the negatively charged first electrode, and a first electrode with a modified surface is obtained.
  • the low molecular weight hydrophobic cations are electrostatically attached to the first electrode to form a cationic layer.
  • the thickness of the cationic layer is preferably three molecular layers or less, more preferably two molecular layers or less, and even more preferably a monolayer or less. In terms of specific thickness, the thickness of the cationic layer is preferably 2 nm or less, and more preferably 1 nm or less. The thickness of the cationic layer can be determined by X-ray photoelectron spectroscopy (XPS) analysis.
  • the first reducing agent that generates low molecular weight hydrophobic cations is also a low molecular weight compound.
  • the surface modification liquid (S1) preferably further contains low molecular weight hydrophobic cations (hereinafter, sometimes referred to as "other low molecular weight hydrophobic cations") different from the low molecular weight hydrophobic cations generated from the first reducing agent.
  • other low molecular weight hydrophobic cations low molecular weight hydrophobic cations
  • electrostatically adhere to the first electrode negatively charged by reduction or the low molecular weight hydrophobic cations derived from the first reducing agent electrostatically attached to the first electrode are replaced by the other low molecular weight hydrophobic cations.
  • a cation layer is formed on the surface of the first electrode by the low molecular weight hydrophobic cations derived from the first reducing agent and the other low molecular weight hydrophobic cations, or the other low molecular weight hydrophobic cations.
  • the molar ratio of the low molecular weight hydrophobic cations derived from the first reducing agent and the other low molecular weight hydrophobic cations in the cation layer can be adjusted by adjusting the concentration or degree of hydrophobicity of the other low molecular weight hydrophobic cations in the surface modification liquid (S1).
  • low molecular weight hydrophobic cations derived from the first reducing agent and other low molecular weight hydrophobic cations may be collectively referred to as “low molecular weight hydrophobic cations" or “low molecular weight hydrophobic ions.”
  • the work function of the first electrode becomes shallower (smaller) than before modification.
  • the shift in the work function of the first electrode due to the electrode modification process in this embodiment is very large; for example, as shown in the examples described later, the work function of a gold electrode shifts from approximately 5.0 eV to approximately 3.7 eV due to surface modification.
  • the electron injection from the first electrode to the organic semiconductor layer is greatly improved.
  • electrons can easily enter the LUMO of the organic semiconductor from the first electrode, and therefore can easily move from the first electrode through the organic semiconductor layer to the second electrode.
  • the electron injection from the second electrode to the organic semiconductor layer is hardly changed, and the movement of electrons from the second electrode to the first electrode is more difficult than the movement of electrons from the first electrode to the second electrode.
  • the surface modification of the first electrode makes it easier for current to flow from the second electrode to the first electrode, and the ease of current flow from the first electrode to the second electrode is hardly changed, and therefore the rectification characteristics of the vertical diode are improved, and the stable operation of the vertical diode can be realized. It is also possible to increase the current density of the vertical diode at low voltage.
  • a vertical diode with excellent rectification characteristics can be obtained by using a layer of an electron transporting organic semiconductor, i.e., a layer of an n-type organic semiconductor, as the organic semiconductor layer and using the first electrode as an electron injection electrode (cathode (negative pole)). Also, a vertical diode that exhibits high current density even at low voltage can be obtained. In this case, it is not necessary for the entire organic semiconductor layer to be an n-type organic semiconductor layer; for example, when the organic semiconductor layer has a multi-layer structure, the above effect can be obtained as long as only the layer adjacent to the first electrode is an n-type organic semiconductor layer.
  • a method of adjusting the work function of an electrode by depositing a polymer or salt on the electrode is known.
  • a polymer layer thicker than a monolayer is formed between the electrode and the organic semiconductor layer, which causes a problem of significantly reducing the electron injection from the electrode to the organic semiconductor layer.
  • a salt of a cationic species and a counter anion such as a halide ion is used as the salt to be deposited on the electrode.
  • This salt not only reduces the electron injection from the electrode to the organic semiconductor layer, but also causes the problem that the halide ions diffuse into the organic semiconductor layer, reducing the life of the device.
  • both the polymer and the salt contain parts other than those responsible for controlling the work function, even when these materials are deposited thinly, so that it is inevitable that an excess function that hinders electron injection occurs.
  • the manufacturing method according to this embodiment has an advantage in principle in semiconductor element manufacturing.
  • low molecular weight hydrophobic cations are attached (adsorbed) to the surface of the negatively charged first electrode by a reduction reaction to form a thin cation layer, effectively suppressing the formation of an excess layer that inhibits electron transfer between the first electrode and the organic semiconductor layer, or the formation of salt. Therefore, in addition to excellent electron transfer between the first electrode and the organic semiconductor layer and the rectification characteristics of the vertical diode, it is also possible to achieve a longer life for the vertical diode and improved current density at low voltage.
  • the first reducing agent is not particularly limited as long as it produces electrons and low molecular weight hydrophobic cations and can reduce the first electrode.
  • the low molecular weight hydrophobic cation generated from the first reducing agent is preferably a low molecular weight hydrophobic cation that is highly hydrophobic and stable against air and water, and is more preferably a low molecular weight hydrophobic closed shell cation. This is because low molecular weight hydrophobic closed shell cations are highly stable in solvents, particularly in water.
  • low molecular weight hydrophobic cations generated from the first reducing agent include low molecular weight hydrophobic closed shell cations represented by formulas (1A) to (1C).
  • the low molecular weight hydrophobic cations generated from the first reducing agent are preferably one or more types selected from the cations represented by formulas (1A) to (1B), and more preferably one or more types selected from the cation represented by formula (1B) in terms of higher stability to air and water.
  • M1 is rhodium or iridium, preferably rhodium.
  • M2 is ruthenium
  • M3 is cobalt.
  • R 1 to R 3 each independently represent a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent.
  • R 1 is preferably a hydrogen atom or an alkyl group which may have a substituent, and more preferably a hydrogen atom or an unsubstituted alkyl group.
  • R2 is preferably a hydrogen atom or an alkyl group which may have a substituent, and more preferably a hydrogen atom or an unsubstituted alkyl group.
  • R3 is preferably a hydrogen atom or an alkyl group which may have a substituent, and more preferably a hydrogen atom or an unsubstituted alkyl group.
  • substituents that the alkyl and aryl groups represented by R 1 to R 3 may have include, but are not limited to, a deuterium atom; a hydroxyl group; a halogen atom such as a fluorine atom, a chlorine atom, or a bromine atom; an alkyl group having 1 to 4 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, or an isopropyl group; a cycloalkyl group such as a cyclopropyl group or a cyclobutyl group; an aryl group having 6 to 12 carbon atoms, such as a phenyl group, a 1-naphthyl group, or a 2-naphthyl group; and an aralkyl group such as a benzyl group or a 2-phenylethyl group.
  • the number of carbon atoms of the alkyl group which may have a substituent represented by R 1 to R 3 is not particularly limited, but is preferably 1 or more and 20 or less, more preferably 1 or more and 12 or less, even more preferably 2 or more and 8 or less, and particularly preferably 2 or more and 6 or less.
  • alkyl group which may have a substituent and which are represented by R 1 to R 3 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an isobutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, a trifluoromethyl group, a pentafluoroethyl group, a hydroxymethyl group, and a 2-hydroxyethyl group, and preferably a methyl group.
  • the number of carbon atoms of the aryl group which may have a substituent and is represented by R 1 to R 3 is not particularly limited, but is preferably 6 or more and 20 or less, and more preferably 6 or more and 14 or less.
  • low molecular weight hydrophobic closed shell cations represented by formula (1A) include the following cations.
  • low molecular weight hydrophobic closed shell cations represented by formula (1B) include the following cations.
  • low molecular weight hydrophobic closed shell cations represented by formula (1C) include the following cations.
  • Examples of the first reducing agent that produces these low molecular weight hydrophobic cations include compounds represented by formulas (2A) to (2C).
  • the compounds represented by formulas (2A) to (2C) are first reducing agents that produce low molecular weight hydrophobic closed shell cations represented by formulas (1A) to (1C), respectively. Therefore, of these, the first reducing agent is preferably one or more types selected from the compounds represented by formulas (2A) to (2B), and more preferably one or more types selected from the compounds represented by formula (2B) in that it can produce low molecular weight hydrophobic closed shell cations that are more stable to air and water.
  • M1 and R1 in formula (2A) have the same meanings as M1 and R1 in formula (1A), and preferred embodiments thereof are also the same.
  • M2 and R2 in formula (2B) have the same meanings as M2 and R2 in formula (1B), and preferred embodiments thereof are also the same.
  • M3 and R3 in formula (2C) have the same meanings as M3 and R3 in formula (1C), and preferred embodiments thereof are also the same.
  • compounds represented by formula (2C) include cobaltocene and decamethylcobaltocene.
  • the first reducing agent may be used alone or in any combination of two or more kinds in any ratio. Therefore, the low molecular weight hydrophobic cation attached to the surface of the first electrode may also be one type or two or more types.
  • the other low molecular weight hydrophobic cations contained in the surface modification liquid (S1) are synonymous with the low molecular weight hydrophobic cations derived from the first reducing agent, and the preferred embodiments are also the same.
  • the low molecular weight hydrophobic cations may be used alone or in any ratio and combination of two or more.
  • the other low molecular weight hydrophobic cations contained in one surface modification liquid (S1) are cations different from the low molecular weight hydrophobic cations derived from the first reducing agent.
  • the counter anion of the other low molecular weight hydrophobic cation contained in the surface modification liquid (S1) is not particularly limited, but may be, for example, a hydroxide ion; halide ions such as chloride ions, bromide ions, and iodide ions; carbonate ions; sulfate ions; and phosphate ions.
  • the counter anion is preferably a hydroxide ion, since it can suppress the deposition of halide salts that inhibit electron injection from the first electrode to the organic semiconductor layer.
  • the total concentration of the first reducing agent in the surface modification liquid (S1) is not particularly limited and may be appropriately selected depending on the type of the first reducing agent, the coverage of the low-molecular-weight hydrophobic ion described below, the shift width of the work function, etc.
  • the total concentration of the first reducing agent is preferably 0.01% by mass or more and 3.00% by mass or less, more preferably 0.10% by mass or more and 1.00% by mass or less.
  • the total concentration of the other low molecular weight hydrophobic cations in the surface modification liquid (S1) is not particularly limited and may be appropriately selected depending on the type of other low molecular weight hydrophobic cations, the low molecular weight hydrophobic ion coverage rate described below, the shift width of the work function, and the proportion of the other low molecular weight hydrophobic cations in all the low molecular weight hydrophobic cations modifying the first electrode.
  • the total concentration of the low molecular weight hydrophobic cations is preferably 0.01 mass% or more and 3.00 mass% or less, more preferably 0.10 mass% or more and 1.00 mass% or less.
  • the first oxidizing agent contained in the surface modifying liquid (S2) is a compound that oxidizes the first electrode and generates low molecular weight hydrophobic anions.
  • the surface modifying liquid (S2) is used as the surface modifying liquid, in this process, holes are injected into the first electrode (i.e., the surface of the first electrode is oxidized), thereby positively charging the surface of the first electrode.
  • low molecular weight hydrophobic anions generated from the first oxidizing agent are electrostatically attached to the surface of the positively charged first electrode, and a first electrode having a modified surface is obtained. At this time, the low molecular weight hydrophobic anions are electrostatically attached to the first electrode to form an anion layer.
  • the thickness of the anion layer is preferably three molecular layers or less, more preferably two molecular layers or less, and even more preferably a monolayer or less. In terms of specific thickness, the thickness of the anion layer is preferably 2 nm or less, and more preferably 1 nm or less.
  • the thickness of the anion layer can be determined by X-ray photoelectron spectroscopy (XPS) analysis.
  • the first oxidizing agent that generates a low-molecular-weight hydrophobic anion is also a low-molecular-weight compound.
  • the surface modification liquid (S2) preferably further contains low molecular weight hydrophobic anions (hereinafter, sometimes referred to as "other low molecular weight hydrophobic anions") different from the low molecular weight hydrophobic anions generated from the first oxidizing agent.
  • other low molecular weight hydrophobic anions low molecular weight hydrophobic anions
  • the other low molecular weight hydrophobic anions electrostatically adhere to the first electrode positively charged by oxidation, or the low molecular weight hydrophobic anions derived from the first oxidizing agent electrostatically attached to the first electrode are replaced by the other low molecular weight hydrophobic anions.
  • an anion layer is formed on the surface of the first electrode by the low molecular weight hydrophobic anions derived from the first oxidizing agent and the other low molecular weight hydrophobic anions, or the other low molecular weight hydrophobic anions.
  • the molar ratio of the low molecular weight hydrophobic anions derived from the first oxidizing agent and the other low molecular weight hydrophobic anions in the anion layer can be controlled by adjusting the concentration or degree of hydrophobicity of the low molecular weight hydrophobic anions in the surface modification liquid (S2).
  • low molecular weight hydrophobic anions derived from the first oxidizing agent and other low molecular weight hydrophobic anions may be collectively referred to as “low molecular weight hydrophobic anions" or “low molecular weight hydrophobic ions.”
  • the work function of the first electrode becomes deeper (larger) than before modification. According to the electrode modification process in this embodiment, the work function of the first electrode can be significantly shifted.
  • the hole injection from the first electrode to the organic semiconductor layer is greatly improved.
  • holes can be easily injected from the first electrode into the HOMO of the organic semiconductor, and can easily move from the first electrode through the organic semiconductor layer to the second electrode.
  • the hole injection from the second electrode to the organic semiconductor layer is hardly changed, and the movement of holes from the second electrode to the first electrode is more difficult than the movement of holes from the first electrode to the second electrode.
  • the surface modification of the first electrode makes it easier for current to flow from the first electrode to the second electrode, and the ease of current flow from the second electrode to the first electrode is hardly changed, and therefore the rectification characteristics of the vertical diode are improved, and the stable operation of the vertical diode can be realized. It is also possible to increase the current density of the vertical diode at low voltage.
  • a vertical diode with excellent rectification characteristics can be obtained by using a hole-transporting organic semiconductor layer, i.e., a p-type organic semiconductor layer, as the organic semiconductor layer and using the first electrode as a hole injection electrode (anode (positive electrode)). Also, a vertical diode that exhibits high current density even at low voltage can be obtained. In this case, it is not necessary for the entire organic semiconductor layer to be a p-type organic semiconductor layer; for example, when the organic semiconductor layer has a multi-layer structure, the above effect can be similarly obtained as long as only the layer adjacent to the first electrode is a p-type organic semiconductor layer.
  • the low molecular weight hydrophobic anion generated from the first oxidizing agent is preferably a low molecular weight hydrophobic anion that is highly hydrophobic and stable against air and water, more preferably a low molecular weight hydrophobic closed shell anion or a low molecular weight hydrophobic radical anion, and even more preferably a low molecular weight hydrophobic closed shell anion. This is because low molecular weight hydrophobic closed shell anions are highly stable in solvents, particularly in water.
  • low molecular weight hydrophobic closed shell anions generated from the first oxidizing agent include FeCl 4 -- and the anions represented by formulae (3A) to (3C).
  • each R 11 is independently a trifluoromethyl group (CF 3 ), a methyloxycarbonyl group (COOMe), or a trifluoromethyloxycarbonyl group (COOCF 3 ).
  • R 12 each independently represents a hydrogen atom, a halogen atom, or an alkyl group which may have a substituent, is preferably a hydrogen atom or a halogen atom, and is more preferably a halogen atom.
  • Examples of the halogen atom represented by R 12 include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and a fluorine atom is preferred.
  • the alkyl group which may have a substituent represented by R 12 has the same meaning as the alkyl group which may have a substituent represented by R 1 to R 3 , and the preferred embodiments thereof are also the same.
  • each R 13 is independently a cyano group (CN) or a methyloxycarbonyl group (COOMe).
  • Examples of the first oxidizing agent that generates a low-molecular-weight hydrophobic closed-shell anion include iron(III) chloride and the compounds represented by formulae (4A) to (4C).
  • Iron(III) chloride is a first oxidizing agent that generates FeCl 4 -
  • the compounds represented by formulae (4A) to (4C) are first oxidizing agents that generate low-molecular-weight hydrophobic closed-shell cations represented by formulae (3A) to (3C), respectively.
  • R 11 in formula (4A) has the same meaning as R 11 in formula (3A), and the preferred embodiments thereof are also the same.
  • R 12 in formula (4B) has the same meaning as R 12 in formula (3B), and the preferred embodiments thereof are also the same.
  • R 13 in formula (4C) has the same meaning as R 13 in formula (3C), and the preferred embodiments thereof are also the same.
  • Examples of the low molecular weight hydrophobic radical anion generated from the first oxidizing agent include radical anions represented by formulas (3D) to (3E). Of these, it is preferable that the low molecular weight hydrophobic radical anion generated from the first oxidizing agent is one or more types selected from the radical anion represented by formula (3D).
  • R 14 and R 15 each independently represent a hydrogen atom, a halogen atom, or an alkyl group which may have a substituent, preferably a hydrogen atom or a halogen atom, more preferably a halogen atom.
  • Examples of the halogen atom represented by R 14 and R 15 include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and a fluorine atom is preferred.
  • the alkyl group which may have a substituent represented by R 14 and R 15 has the same meaning as the alkyl group which may have a substituent represented by R 1 to R 3 , and the preferred embodiments thereof are also the same.
  • low molecular weight hydrophobic radical anions represented by formula (3D) include the following anions.
  • low molecular weight hydrophobic radical anion represented by formula (3E) include the following anions.
  • First oxidizing agents that generate low molecular weight hydrophobic radical anions include compounds represented by formulas (4D) to (4E).
  • the compounds represented by formulas (4D) to (4E) are first oxidizing agents that generate low molecular weight hydrophobic radical cations represented by formulas (3D) to (3E), respectively. Therefore, of these, it is preferable that the first oxidizing agent is one or more types selected from the compounds represented by formula (4D).
  • R 14 in formula (4D) has the same meaning as R 14 in formula (3D), and the preferred embodiments thereof are also the same.
  • R 15 in formula (4E) has the same meaning as R 15 in formula (3E), and the preferred embodiments thereof are also the same.
  • the first oxidizing agent may be used alone or in any combination of two or more kinds in any ratio. Accordingly, the low molecular weight hydrophobic anion attached to the surface of the first electrode may also be one type or two or more types.
  • the other low molecular weight hydrophobic anion contained in the surface modification liquid (S2) is synonymous with the low molecular weight hydrophobic anion derived from the first oxidizing agent, and the preferred embodiments are also the same.
  • the low molecular weight hydrophobic anion may be used alone or in any ratio and combination of two or more types.
  • the other low molecular weight hydrophobic anion contained in one surface modification liquid (S2) is an anion different from the low molecular weight hydrophobic anion derived from the first reducing agent.
  • the counter cation of the other low molecular weight hydrophobic anion contained in the surface modification liquid (S2) is not particularly limited, but may be, for example, a proton; or a metal ion such as a lithium ion, a sodium ion, or a potassium ion.
  • the counter cation is preferably a proton, since it can suppress the deposition of metal salts that inhibit hole injection from the first electrode to the organic semiconductor layer.
  • the total concentration of the first oxidizing agent in the surface modification liquid (S2) is not particularly limited and may be appropriately selected depending on the type of first oxidizing agent, the coverage of low-molecular-weight hydrophobic ions described below, the shift width of the work function, and the like.
  • the total concentration of the first oxidizing agent is preferably 0.01% by mass or more and 3.00% by mass or less, and more preferably 0.10% by mass or more and 1.00% by mass or less.
  • the total concentration of the other low molecular weight hydrophobic anions in the surface modification liquid (S2) is not particularly limited and may be appropriately selected depending on the type of the other low molecular weight hydrophobic anions, the low molecular weight hydrophobic ion coverage rate described below, the shift width of the work function, and the proportion of the other low molecular weight hydrophobic anions in the total low molecular weight hydrophobic anions modifying the first electrode.
  • the total concentration of the low molecular weight hydrophobic anions is preferably 0.01% by mass or more and 3.00% by mass or less, more preferably 0.10% by mass or more and 1.00% by mass or less.
  • the second reducing agent contained in the surface modifying liquid (S3) is a compound that reduces the first electrode and does not generate low molecular weight hydrophobic cations. Moreover, the second reducing agent is preferably a compound that does not generate any cationic species other than the low molecular weight hydrophobic cations during the reduction of the first electrode. This is because the second reducing agent does not generate any cationic species, and thus the low molecular weight hydrophobic closed shell cations contained in the surface modifying liquid (S3) can be selectively attached to the surface of the first electrode.
  • the second reducing agent the same as the third reducing agent described later can be used, and compounds that are preferred as the third reducing agent are also preferred as the second reducing agent. That is, examples of the second reducing agent include hydroquinone compounds having a hydroquinone skeleton, which are described later as the third reducing agent; dihydroxyfuranone compounds having a dihydroxyfuranone skeleton; sugars having reducing properties; and reduced coenzymes; and the like.
  • the second reducing agent is preferably one or more selected from the group consisting of hydroquinone compounds having a hydroquinone skeleton and reduced coenzymes, and more preferably a reduced coenzyme.
  • the low molecular weight hydrophobic closed shell cation contained in the surface modification liquid (S3) is one that is unlikely to undergo an oxidation-reduction reaction with water or an oxidation-reduction reaction with oxygen under temperature conditions of 15°C or higher and 35°C or lower (room temperature conditions) and in the air.
  • Such low molecular weight hydrophobic closed shell cations are preferably those represented by formulas (1D) to (1F) in addition to the low molecular weight hydrophobic closed shell cations generated from the first reducing agent.
  • R 4 to R 6 each independently represent a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent.
  • the alkyl group which may have a substituent and the aryl group which may have a substituent represented by R4 to R6 have the same meaning as the alkyl group which may have a substituent and the aryl group which may have a substituent represented by R1 to R3, respectively.
  • R4 is preferably an alkyl group which may have a substituent or an aryl group which may have a substituent, more preferably an aryl group which may have a substituent, and further preferably an unsubstituted aryl group.
  • R5 is preferably an alkyl group which may have a substituent or an aryl group which may have a substituent, more preferably an aryl group which may have a substituent, and further preferably an unsubstituted aryl group.
  • R6 is preferably an alkyl group which may have a substituent or an aryl group which may have a substituent, and more preferably an unsubstituted alkyl group or an aryl group which may have a substituent.
  • low molecular weight hydrophobic closed shell cations represented by formula (1D) include the following cations.
  • low molecular weight hydrophobic closed shell cations represented by formula (1E) include the following cations.
  • low molecular weight hydrophobic closed shell cations represented by formula (1F) include the following cations.
  • the counter anion of the low molecular weight hydrophobic closed shell cation contained in the surface modification liquid (S3) is not particularly limited, but examples thereof include hydroxide ions; halide ions such as chloride ions, bromide ions, and iodide ions; carbonate ions; sulfate ions; and phosphate ions.
  • the counter anion is preferably a hydroxide ion, since it can suppress the deposition of halide salts that inhibit electron injection from the first electrode to the organic semiconductor layer.
  • the total concentration of the second reducing agent in the surface modification liquid (S3) is not particularly limited and may be appropriately selected depending on the type of the second reducing agent and the shift width of the work function.
  • the total concentration of the second reducing agent is preferably 0.01% by mass or more and 3.00% by mass or less, and more preferably 0.10% by mass or more and 1.00% by mass or less.
  • the total concentration of low molecular weight hydrophobic closed shell cations in the surface modification liquid (S3) is not particularly limited and may be appropriately selected depending on the type of low molecular weight hydrophobic closed shell cation, the low molecular weight hydrophobic ion coverage rate described below, and the shift width of the work function.
  • the total concentration of low molecular weight hydrophobic closed shell cations is preferably 0.01 mass% or more and 3.00 mass% or less, more preferably 0.10 mass% or more and 1.00 mass% or less.
  • the total concentration of the halide ions in the surface modification liquid (S3) is preferably 100 ppm by mass or less, more preferably 10 ppm by mass or less, and even more preferably 1 ppm by mass or less.
  • the surface modification liquid (S3) is used as the surface modification liquid, in this process, electrons are injected into the first electrode (i.e., the surface of the first electrode is reduced), causing the surface of the first electrode to become negatively charged. Then, low molecular weight hydrophobic closed shell cations are electrostatically attached to the negatively charged surface of the first electrode, resulting in a surface-modified first electrode. At this time, as in the case of using the surface modification liquid (S1), low molecular weight hydrophobic closed shell cations are electrostatically attached to the surface of the first electrode, forming a cationic layer with a thickness of less than a monolayer. The thickness of the cationic layer can be determined by X-ray photoelectron spectroscopy (XPS) analysis.
  • XPS X-ray photoelectron spectroscopy
  • the surface modification liquid (S3) when used as the surface modification liquid, the surface of the first electrode is modified in the same way as when the surface modification liquid (S1) is used. Therefore, when the surface modification liquid (S3) is used as the surface modification liquid, the work function of the first electrode can be made shallow (small) in the same way as when the surface modification liquid (S1) is used, and the rectification characteristics of the vertical diode can be improved. It is also possible to increase the current density of the vertical diode at low voltages.
  • a vertical diode with excellent rectification characteristics can be obtained by using an electron transporting organic semiconductor layer, i.e., an n-type organic semiconductor layer, as the organic semiconductor layer and using the first electrode as an electron injection electrode (cathode (negative pole)). Also, a vertical diode that exhibits high current density even at low voltage can be obtained. In this case, it is not necessary for the entire organic semiconductor layer to be an n-type organic semiconductor layer; for example, when the organic semiconductor layer has a multi-layer structure, the above effect can be obtained as long as only the layer adjacent to the first electrode is an n-type organic semiconductor layer.
  • the second oxidizing agent contained in the surface modifying liquid (S4) is a compound that oxidizes the first electrode and does not generate low molecular weight hydrophobic anions. Moreover, the second oxidizing agent is preferably a compound that does not generate any anion species other than the low molecular weight hydrophobic anions during the oxidation of the first electrode. This is because the second oxidizing agent does not generate any anion species, and thus the low molecular weight hydrophobic closed shell anions contained in the surface modifying liquid (S4) can be selectively attached to the surface of the first electrode.
  • the second oxidizing agent the same as the third oxidizing agent described later can be used, and compounds that are preferred as the third oxidizing agent are also preferred as the second oxidizing agent.
  • examples of the second oxidizing agent include quinone compounds having a quinone skeleton, which are described later as the third oxidizing agent; furantrione compounds having a furantrione skeleton; and radical compounds; and the like, with quinone compounds having a quinone skeleton being preferred.
  • the low molecular weight hydrophobic closed shell anion contained in the surface modification liquid (S4) is one that is unlikely to undergo an oxidation-reduction reaction with water or an oxidation-reduction reaction with oxygen under temperature conditions of 15°C or higher and 35°C or lower (room temperature conditions) and in the air.
  • Such low molecular weight hydrophobic closed shell anions are preferably those represented by formulae (3F) to (3G) in addition to the low molecular weight hydrophobic closed shell anions generated from the first oxidizing agent.
  • R 14 is each independently a hydrogen atom, a halogen atom, or an optionally substituted fluorinated alkyl group, and is preferably a halogen atom.
  • each R 15 is independently a perfluoroalkyl group, and two R 15s may be linked to each other to form a ring.
  • Examples of the halogen atom represented by R 14 include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and preferably a chlorine atom or a fluorine atom, and more preferably a fluorine atom.
  • Examples of the substituent that the fluorinated alkyl group represented by R 14 may have include, but are not limited to, the same as the substituent that the alkyl group and aryl group represented by R 1 to R 3 may have. Note that in the fluorinated alkyl group, the substituent is a group that replaces a hydrogen atom bonded to a carbon atom of the fluorinated alkyl group.
  • the number of carbon atoms of the fluorinated alkyl group which may have a substituent and is represented by R 14 is not particularly limited, but is preferably 1 or more and 10 or less, more preferably 1 or more and 6 or less, and further preferably 2 or more and 4 or less.
  • fluorinated alkyl group which may have a substituent represented by R 14 include a trifluoromethyl group, a pentafluoroethyl group, a pentafluoro-n-propyl group, and a 1,1,1,3,3,3-hexafluoro-2-methoxy-2-propyl group, and preferably a trifluoromethyl group.
  • the number of carbon atoms in the perfluoroalkyl group represented by R 15 is not particularly limited, but is preferably 1 to 20, more preferably 1 to 12, even more preferably 2 to 8, and particularly preferably 2 to 6.
  • perfluoroalkyl group represented by R 15 examples include a perfluoromethyl group (a trifluoromethyl group), a perfluoroethyl group, a perfluoro-n-propyl group, a perfluoroisopropyl group, a perfluoro-n-butyl group, a perfluoroisobutyl group, a perfluoro-sec-butyl group, a perfluoro-tert-butyl group, a perfluoro-n-pentyl group, a perfluoroneopentyl group, a perfluoro-n-hexyl group, a perfluorocyclohexyl group, and the like, and preferred are a perfluoromethyl group and a perfluoro-n-butyl group.
  • low molecular weight hydrophobic closed shell anions represented by formula (3F) include tetraphenylborate anion, tetrakis(p-tolyl)borate anion, tetrakis(p-trifluoromethylphenyl)borate anion, tetrakis(p-fluorophenyl)borate anion, tetrakis(perfluorophenyl)borate anion, and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion, with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion being preferred.
  • low molecular weight hydrophobic closed shell anions represented by formula (3G) include bis(trifluoromethanesulfonyl)imide anion, bis(perfluoroethanesulfonyl)imide anion, bis(perfluoropropanesulfonyl)imide anion, bis(perfluorobutanesulfonyl)imide anion, and cyclohexafluoropropane-1,3-bis(sulfonyl)imide anion, with bis(trifluoromethanesulfonyl)imide anion being preferred.
  • the counter cation of the low molecular weight hydrophobic closed shell anion contained in the surface modification liquid (S4) is not particularly limited, but examples include protons and metal ions such as lithium ions, sodium ions, and potassium ions. Of these, the counter cation is preferably a proton, since it can suppress the deposition of metal salts that inhibit hole injection from the first electrode to the organic semiconductor layer.
  • the total concentration of the metal ion in the surface modification liquid (S3) is preferably 10,000 mass ppm or less, more preferably 1,000 mass ppm or less, and even more preferably 100 mass ppm or less.
  • the total concentration of the second oxidizing agent in the surface modification liquid (S4) is not particularly limited and may be appropriately selected depending on the type of second oxidizing agent and the shift width of the work function.
  • the total concentration of the second oxidizing agent is preferably 0.01% by mass or more and 3.00% by mass or less, and more preferably 0.10% by mass or more and 1.00% by mass or less.
  • the total concentration of the low molecular weight hydrophobic closed shell anions in the surface modification liquid (S4) is not particularly limited and may be appropriately selected depending on the type of low molecular weight hydrophobic closed shell anions, the low molecular weight hydrophobic ion coverage rate described below, the shift width of the work function, etc.
  • the total concentration of the low molecular weight hydrophobic closed shell anions is preferably 0.01 mass% or more and 3.00 mass% or less, more preferably 0.10 mass% or more and 1.00 mass% or less.
  • the surface modification liquid (S4) is used as the surface modification liquid, in this process, holes are injected into the first electrode (i.e., the surface of the first electrode is oxidized), so that the surface of the first electrode becomes positively charged. Then, low molecular weight hydrophobic closed shell anions are electrostatically attached to the surface of this positively charged first electrode, and a surface-modified first electrode is obtained. At this time, as in the case of using the surface modification liquid (S2), low molecular weight hydrophobic closed shell anions are electrostatically attached to the surface of the first electrode, and an anion layer with a thickness of less than a monolayer is formed. The thickness of the anion layer can be determined by X-ray photoelectron spectroscopy (XPS) analysis.
  • XPS X-ray photoelectron spectroscopy
  • the surface modification liquid (S4) when used as the surface modification liquid, the surface of the first electrode is modified in the same way as when the surface modification liquid (S2) is used. Therefore, when the surface modification liquid (S4) is used as the surface modification liquid, the work function of the first electrode can be deepened (increased) in the same way as when the surface modification liquid (S2) is used, and the rectification characteristics of the vertical diode can be improved. It is also possible to increase the current density of the vertical diode at low voltages.
  • a vertical diode with excellent rectification characteristics can be obtained by using a layer of a hole-transporting organic semiconductor, i.e., a layer of a p-type organic semiconductor, as the organic semiconductor layer and using the first electrode as a hole injection electrode (anode (positive electrode)).
  • a layer of a hole-transporting organic semiconductor i.e., a layer of a p-type organic semiconductor
  • the first electrode as a hole injection electrode (anode (positive electrode)
  • the entire organic semiconductor layer it is not necessary for the entire organic semiconductor layer to be a layer of a p-type organic semiconductor.
  • the organic semiconductor layer has a multi-layer structure, the above effect can be obtained as long as only the layer adjacent to the first electrode is a layer of a p-type organic semiconductor.
  • the surface modification liquid (S4) When the surface modification liquid (S4) is used to modify the first electrode, problems such as the formation of an excess layer between the first electrode and the organic semiconductor layer that inhibits hole injection and the formation of salt are effectively suppressed for the same reasons as when the surface modification liquid (S2) is used. This makes it possible to improve the hole injection from the first electrode to the organic semiconductor layer, and also to realize improved rectification characteristics of the vertical diode, longer life, and improved current density at low voltage.
  • the solvent of the surface modifying liquids (S1) to (S4) may be an organic solvent, water, or a mixed solvent of an organic solvent and water. From the viewpoints of reducing production costs, improving workability, and reducing the environmental load, water is preferred.
  • the water is not particularly limited, and may be tap water; pure water such as distilled water, RO water, and deionized water; and ultrapure water with a resistivity of 18 M ⁇ or more; but is preferably pure water, and more preferably deionized water.
  • RO water means water filtered through a reverse osmosis membrane.
  • the organic solvent is not particularly limited as long as it can dissolve or disperse the low molecular weight reducing agent or low molecular weight oxidizing agent, and examples thereof include alcohols such as methanol, ethanol, and n-propanol; hydrocarbons such as hexane, benzene, toluene, and xylene; ethers such as diethyl ether, 1,4-dioxane, diglyme, and tetrahydrofuran (THF); esters such as ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; halogenated hydrocarbon solvents such as 1,2-dichloroethane and chloroform; nitrile solvents such as acetonitrile and benzonitrile; amides such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (D
  • any of the organic solvents described above that is miscible with water can be used.
  • the content of water in the mixed solvent is not particularly limited as long as the two can be mixed uniformly, and examples of the content include ranges of 5% by mass or more and less than 100% by mass, 40% by mass or more and 95% by mass or less, 60% by mass or more and 90% by mass or less, and 80% by mass or more and 90% by mass or less.
  • the surface modifying liquids (S1) to (S4) may contain one or more components other than the above-mentioned components, as long as the effects of the present disclosure are not impaired.
  • the surface modifying solutions (S1) and (S2) are prepared by dissolving a first reducing agent and a second oxidizing agent, respectively, in a solvent.
  • the surface modification liquid (S3) is prepared by dissolving the second reducing agent and a compound containing a low molecular weight hydrophobic cation as a cationic component in a solvent.
  • the compound is preferably a salt formed from a low molecular weight hydrophobic cation and an anionic component such as a hydroxide ion; a halide ion such as a chloride ion, a bromide ion, or an iodide ion; a carbonate ion; a sulfate ion; or a phosphate ion.
  • the compound is more preferably a halide salt formed from a low molecular weight hydrophobic cation and a halide ion.
  • the resulting surface modification liquid (S3) contains a halide ion as a counter anion of the low molecular weight hydrophobic cation. Therefore, when a halide salt is used to prepare the surface modification liquid (S3), it is preferable to contact the solution obtained by dissolving the halide salt in a solvent with an anion exchange resin and exchange the halide ions in the solution for hydroxide ions, thereby reducing the total concentration of the halide ions to the preferred range described above. Any known anion exchange resin can be used as the anion exchange resin.
  • the surface modification liquid (S4) is prepared by dissolving the second oxidizing agent and a compound containing a low molecular weight hydrophobic anion as an anion component in a solvent.
  • the compound is preferably a metal salt formed from a low molecular weight hydrophobic anion and a metal ion such as a lithium ion, a sodium ion, or a potassium ion.
  • the resulting surface modification liquid (S4) contains a metal ion as a counter cation for the low molecular weight hydrophobic anion. Therefore, when a metal salt is used to prepare the surface modification liquid (S4), it is preferable to contact the solution obtained by dissolving the metal salt in a solvent with a cation exchange resin and exchange the metal ions in the solution for protons, thereby reducing the total concentration of the metal ions to the preferred range described above. Any known cation exchange resin can be used as the cation exchange resin.
  • the cathode has a work function smaller than the LUMO of the organic semiconductor constituting the organic semiconductor layer and smaller than the anode, and it is also desirable that the anode has a work function larger than the LUMO of the organic semiconductor constituting the organic semiconductor layer.
  • the first electrode when the first electrode is a cathode (negative electrode; electron injection electrode), it is desirable that the first electrode, after the electrode modification step, has a work function smaller than the LUMO of the organic semiconductor constituting the organic semiconductor layer (when the organic semiconductor layer has a multilayer structure, the organic semiconductor constituting the layer adjacent to the first electrode) and a work function smaller than that of the second electrode. Also, when the first electrode is an anode (positive electrode; hole injection electrode), it is desirable that the first electrode exhibits a work function larger than the second electrode and the organic semiconductor constituting the organic semiconductor layer (when the organic semiconductor layer has a multilayer structure, the organic semiconductor constituting the layer adjacent to the second electrode).
  • the material constituting the first electrode is appropriately selected depending on the organic semiconductor and the second electrode, but since this process can significantly shift the work function of the first electrode and easily adjust it to the desired work function, there are no particular limitations as long as the material is conductive.
  • Specific electrode materials include, for example, metals such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, magnesium, molybdenum, and tungsten; alloys containing two or more of these metals; and metal oxides such as indium oxide, tin oxide, zinc oxide, indium tin oxide (ITO), and indium zinc oxide (IZO).
  • the work function of a gold electrode can be shifted from about 5.0 eV to about 3.7 eV by contacting it with a surface modification solution containing a low-molecular-weight reducing agent. Therefore, by using a surface-modified gold electrode, an organic semiconductor layer with a LUMO of about 4.0, and an unmodified gold electrode as the first electrode, organic semiconductor layer, and second electrode, respectively, a vertical diode with excellent rectification characteristics, preferably a vertical diode with excellent rectification characteristics and high current density at low voltage, can be obtained. Furthermore, even if the surface-modified gold electrode is replaced with a surface-modified copper electrode or a surface-modified ITO electrode, a vertical diode with excellent rectification characteristics can be obtained by the same principle.
  • this embodiment can provide a vertical diode with good rectification characteristics, in which either or both of the first and second electrodes are copper electrodes or ITO electrodes, and preferably in which the first electrode is a copper electrode or ITO electrode.
  • the thickness of the first electrode is not particularly limited and may be adjusted appropriately taking into consideration the application of the vertical diode and the element life, etc.
  • Specific examples of the thickness of the second electrode include 10 nm or more and 200 nm or less, and preferably 20 nm or more and 50 nm or less.
  • the second electrode can be produced by any method, including known methods and methods similar thereto.
  • Known methods for producing the second electrode include, for example, vacuum deposition, sputtering, chemical vapor deposition, and plating.
  • the method for contacting the surface of the first electrode with the surface modifying liquid is not particularly limited and can be appropriately selected from any process such as a known solution process or a process equivalent thereto.
  • known solution processes include a method of immersing the first electrode in the surface modifying liquid, and a method of applying the surface modifying liquid to the first electrode by any application method such as spin coating, spray coating, and roll coating.
  • the electrode modification step can be carried out in an inert atmosphere such as argon or nitrogen, or in the air.
  • an inert atmosphere such as argon or nitrogen
  • the surface-modified electrode obtained by this step is highly stable to water and air, so the effect of surface modification can be fully obtained even if the electrode modification step is carried out by a solution process using an aqueous solution in the air. Therefore, in terms of good workability and advantages for industrialization, it is preferable to carry out the electrode modification step in the air.
  • the temperature when the surface of the first electrode is brought into contact with the surface modifying liquid is not particularly limited, but is preferably 5° C. or higher and 50° C. or lower, more preferably 15° C. or higher and 35° C. or lower.
  • the time for which the surface of the first electrode is in contact with the surface modifying liquid is not particularly limited, but is preferably from 1 second to 10 hours.
  • the contact conditions between the surface of the first electrode and the surface modifying liquid are preferably adjusted so that the proportion of low molecular weight hydrophobic ions occupying the surface of the first electrode adjacent to the organic semiconductor layer when a vertical diode is fabricated, i.e., the coverage rate of that surface by the layer of low molecular weight hydrophobic ions (hereinafter sometimes referred to as the "low molecular weight hydrophobic ion coverage rate"), falls within the range described below. This is because by setting the low molecular weight hydrophobic ion coverage rate within a specified range, it is possible to significantly change the work function of the first electrode.
  • the coverage rate of low molecular weight hydrophobic ions can be adjusted by adjusting the concentration of the low molecular weight hydrophobic ions; the concentration of the oxidizing agent or reducing agent; and, if the solvent contains water, adjusting the pH of the solvent.
  • the coverage rate tends to increase as the pH becomes lower, and when the electrode surface is reduced, the coverage rate tends to increase as the pH becomes higher.
  • the organic semiconductor layer of the vertical diode to be manufactured preferably has a doped layer and an undoped layer. Therefore, the manufacturing method according to this embodiment preferably includes a doping step of forming the doped layer by contacting an aqueous solution containing one or more selected from the group consisting of a third oxidizing agent and a third reducing agent and a salt of a dopant ion (hereinafter, sometimes referred to as a "doping solution”) with the surface of the organic semiconductor layer precursor.
  • the surface of the organic semiconductor layer to be contacted with the doping solution in the doping step is the surface adjacent to the second electrode when the vertical diode is manufactured.
  • the dope solution is brought into contact with the surface of the organic semiconductor layer precursor, causing an oxidation or reduction reaction of the organic semiconductor (i.e., carriers are injected into the organic semiconductor layer precursor), and as a result, dopant ions are introduced into the organic semiconductor layer precursor, forming a doped layer.
  • This process can achieve efficient doping even when performed in an air atmosphere.
  • the doping process in this embodiment is carried out by coexisting a third oxidizing agent that oxidizes an organic semiconductor by electron transfer or proton-coupled electron transfer in a pH-adjusted aqueous solution, or a third reducing agent that reduces an organic semiconductor by electron transfer or proton-coupled electron transfer, with a salt of a doping ion, thereby exerting a synergistic effect and making it possible to perform chemical doping of an organic semiconductor in the presence of oxygen and water.
  • the doping solution used in the doping step is an aqueous solution containing at least one selected from a third oxidizing agent and a third reducing agent, and a salt of a dopant ion.
  • the third oxidizing agent is a compound that injects holes into the organic semiconductor layer precursor to oxidize the organic semiconductor.
  • the third reducing agent is a compound that injects electrons into the organic semiconductor layer precursor to reduce the organic semiconductor that constitutes the organic semiconductor layer.
  • k protons and k electrons move in a concerted manner.
  • k is an integer of 1 or more, preferably 1 to 4, more preferably 1 to 2.
  • benzoquinone which is a third oxidizing agent, moves two protons and two electrons in a concerted manner to oxidize an organic semiconductor. It is preferable to use two or more third oxidizing agents with different k in combination as the third oxidizing agent. It is also preferable to use two or more third reducing agents with different k in combination as the third reducing agent. This makes it possible to reduce the effect of external conditions, such as the pH of the dope solution, on doping.
  • the third oxidizing agent and the third reducing agent are not particularly limited as long as they are compounds that cause an oxidation reaction or a reduction reaction by electron transfer or proton-coupled electron transfer, and any compound can be used.
  • Suitable third oxidizing agents include compounds that cause an oxidation reaction or a reduction reaction involving protons (i.e., compounds whose redox potential described by the Nernst equation is proportional to pH) and chemical species whose redox potential matches the HOMO level of the organic semiconductor (i.e., chemical species that act as an oxidizing agent).
  • Suitable third reducing agents include compounds that cause a reduction reaction involving protons (i.e., compounds whose redox potential described by the Nernst equation is proportional to pH) and chemical species whose redox potential matches the LUMO level of the organic semiconductor (i.e., chemical species that act as a reducing agent).
  • Quinone compounds include, for example, compounds represented by formulas (Q1) to (Q4).
  • R Q1 to R Q6 are each independently a monovalent functional group; m1 is an integer of 0 to 4; m2 is an integer of 0 to 2; m3 is an integer of 0 to 4; m4 is an integer of 0 to 4; m5 is an integer of 0 to 4; and m6 is an integer of 0 to 4.
  • R Q1 to R Q6 are each independently a monovalent functional group. Adjacent R Q1 to R Q6 may be bonded to each other to form a ring.
  • the ring thus formed is preferably a 5- to 7-membered ring.
  • the monovalent functional group represented by R Q1 to R Q6 is not particularly limited, but may include an alkyl group (preferably having 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms), an alkenyl group (preferably having 2 to 12 carbon atoms, more preferably 2 to 6 carbon atoms), an aryl group (preferably having 6 to 22 carbon atoms, more preferably 6 to 14 carbon atoms), an aralkyl group (preferably having 6 to 22 carbon atoms, more preferably 6 to 14 carbon atoms), an alkoxy group (preferably having 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms), a hydroxy group, a carboxy group, a mercapto group, an amino group, a halogen atom (such as a chlorine atom or a bromine atom), an alkyl ether group, a carboxylate group, a sulfonic acid group, a formyl group, a nitro group, a cyano group, and
  • the monovalent functional group may be a group in which the above functional groups are bonded via a divalent linking group such as -O-, -NR-, -S-, -CO-, -COO-, and -CONH-.
  • the alkyl group and the alkenyl group may be linear, branched, or cyclic.
  • R Q1 to R Q6 is one or more selected from an alkyl group, an alkoxy group, an alkyl ether group, a carboxylate group, a halogen atom, a hydroxy group, an amino group, a carboxyl group, a sulfonic acid group, an aldehyde group, a nitro group, a cyano group, a thiol group, and a silyl group.
  • one or more may be a hydrophilic group such as an alkoxy group, a hydroxy group, a carboxy group, a sulfonic acid group, or an amino group, which is preferable since the hydrophilicity of the compound can be adjusted.
  • R Q1 to R Q6 By making one or more of R Q1 to R Q6 an electron-withdrawing group or an electron-donating group, the redox potential of the compound can be adjusted, which is preferable.
  • An electron-withdrawing group increases the oxidizing power of the compound and decreases the reducing power.
  • an electron-donating group decreases the oxidizing power of the compound and increases the reducing power. That is, R Q1 to R Q6 can be selected so as to match the HOMO level or LUMO level of the organic semiconductor used, thereby adjusting the redox action.
  • m1 is an integer of 0 to 4, preferably an integer of 0 to 2, and more preferably an integer of 0 to 1.
  • m2 is an integer of 0 to 2, preferably an integer of 0 to 1.
  • m3 is an integer of 0 to 4, preferably an integer of 0 to 2, and more preferably an integer of 0 to 1.
  • m4 is an integer of 0 to 4, preferably an integer of 0 to 2, and more preferably an integer of 0 to 1.
  • m5 is an integer of 0 to 4, preferably an integer of 1 to 2.
  • m6 is an integer of 0 to 4, preferably an integer of 0 to 2, and more preferably an integer of 0 to 1.
  • quinone compounds include p-benzoquinone, 2,5-dihydroxy-p-benzoquinone, 2-hydroxy-p-benzoquinone, tetrahydroxy-p-benzoquinone, 1,4-naphthoquinone, 2-hydroxy-1,4-naphthoquinone, 2-methyl-p-benzoquinone, 2-methyl-1,4-naphthoquinone, 2,5-dimethoxy-1,4-benzoquinone, 2,5-di-tert-butyl-1,4-naphthoquinone, and anthraquinone.
  • the quinone compounds described in JP-T-2018-520455 can also be used as the third oxidizing agent in this embodiment.
  • furantrione compound is a compound represented by formula (Q5).
  • R Q7 and R Q8 are each a hydrogen atom or a monovalent functional group.
  • the monovalent functional groups represented by R Q7 and R Q8 have the same meanings as the monovalent functional groups represented by R Q1 to R Q6 , and preferred embodiments thereof are also the same.
  • radical compounds include 2,2-diphenyl-1-picrylhydrazyl (DPPH), 4-hydroxy-2,2,6,6-tetramethyl-piperidine 1-oxyl (TEMPOL), 2,2,6,6-tetramethyl-piperidinyloxyl (TEMPO), 2,6-di-tert-butyl- ⁇ -(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadiene-1-ylidene)-p-tolyloxy, free radical (galvinoxyl, free radical), and triphenylmethyl radical.
  • DPPH 2,2-diphenyl-1-picrylhydrazyl
  • TEMPOL 4-hydroxy-2,2,6,6-tetramethyl-piperidine 1-oxyl
  • TEMPO 2,2,6,6-tetramethyl-piperidinyloxyl
  • R F1 is a monovalent functional group
  • R F2 is O or S, and is preferably O.
  • the monovalent functional group represented by R F1 is not particularly limited, and preferred examples thereof include a hydrogen atom, a hydroxy group, a carboxy group, an amino group, a (meth)acryloyl group, a (meth)acrylamide group, a hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom, and an alkoxy group having 1 to 20 carbon atoms.
  • R F1 is preferably a hydrophilic group in that the water solubility of the compound represented by formula (F1) is improved.
  • Preferred examples of the hydrophilic group include a hydroxy group, a carboxy group, a (meth)acryloyl group, a (meth)acrylamide group, and an alkoxy group (a methoxy group, an ethoxy group).
  • synthetic products may be used, or commercially available products such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO methacrylate), 4-acetamido-TEMPO, 4-hydroxy-TEMPO (TEMPOL), 4-oxo-TEMPO, 4-hydroxy-TEMPO benzoate, 4-(2-iodoacetamido)-TEMPO, 4-amino-TEMPO, and 4-carboxy-TEMPO may be used.
  • TEMPO 2,2,6,6-tetramethylpiperidine 1-oxyl
  • TEMPO methacrylate 4-acetamido-TEMPO
  • 2-hydroxy-TEMPO 4-hydroxy-TEMPO
  • 4-oxo-TEMPO 4-hydroxy-TEMPO benzoate
  • 4-(2-iodoacetamido)-TEMPO 4-amino-TEMPO
  • 4-carboxy-TEMPO may be used.
  • the third oxidizing agent may be used alone or in any combination of two or more kinds in any ratio.
  • the third oxidizing agent is preferably one or more selected from quinone compounds and furantrione compounds, preferably one or more selected from compounds represented by formulas (Q1) to (Q5), and preferably one or more selected from compounds represented by formula (Q1).
  • the compounds represented by formulas (Q1) to (Q5) are contained in the dope solution together with their reduced forms. This allows for more precise control of the redox potentials of the compounds represented by formulas (Q1) to (Q5), and as a result, allows for more precise control of the Fermi level of the organic semiconductor contained in the dope layer.
  • the third reducing agent is preferably one or more selected from the group consisting of hydroquinone compounds having a hydroquinone skeleton and reduced coenzymes, and more preferably a reduced coenzyme.
  • hydroquinone compounds include compounds represented by formulas (Q1') to (Q4').
  • Compounds represented by formulas (Q1') to (Q4') are reduced forms of compounds represented by formulas (Q1) to (Q4), respectively.
  • R Q1 to R Q6 have the same meanings as R Q1 to R Q6 in the formulae (Q1) to (Q4), respectively, and the preferred embodiments thereof are also the same.
  • hydroquinone compounds include p-hydroquinone, 1,2,4,5-benzenetetraol, 1,2,4-benzenetriol, benzenehexaol, 1,4-naphthalenediol, 1,2,5-naphthalenetriol, 2-methyl-1,4-benzenediol, 2-methyl-1,4-naphthalenediol, 2,5-dimethoxy-1,4-benzenediol, 2,5-di-tert-butyl-1,4-naphthalenediol, and 9,10-anthracenediol.
  • the reduced form of the quinone compound described in JP-T-2018-520455 can also be used as the third reducing agent in this embodiment.
  • dihydroxyfuranone compound is a compound represented by formula (Q5').
  • the compound represented by formula (Q5') is a reduced form of the compound represented by formula (Q5).
  • R 8 and R 9 are respectively defined as R 8 and R 9 in formula (Q5), and the preferred embodiments thereof are also the same.
  • reducing sugars examples include fructose, glucose, galactose, maltose, lactose, and cellobiose, with fructose being preferred.
  • the oxidized flavin mononucleotide receives electrons from fructose to generate reduced flavin mononucleotide in the system, and this reduced flavin mononucleotide injects electrons into the organic semiconductor layer precursor.
  • the third reducing agent may be used alone or in any combination of two or more kinds in any ratio.
  • the third reducing agent is preferably one or more selected from hydroquinone compounds and dihydroxyfuranone compounds, preferably one or more selected from compounds represented by formulas (Q1') to (Q5'), and preferably one or more selected from compounds represented by formula (Q1').
  • the compounds represented by formulas (Q1') to (Q5') are contained in the dope solution together with their oxidized forms. This allows for more precise control of the redox potentials of the compounds represented by formulas (Q1') to (Q5'), and as a result, allows for more precise control of the Fermi level of the organic semiconductor contained in the dope layer.
  • the dope solution may contain either the third oxidizing agent or the third reducing agent along with the salt of the dopant ion, but it is also preferable that the dope solution contains both the third oxidizing agent and the third reducing agent. This is because the dope solution containing both the third oxidizing agent and the third reducing agent can more stably control the redox potential of the dope solution and the Fermi level of the organic semiconductor.
  • the dope solution contains both the third oxidizing agent and the third reducing agent, the ratio of the third oxidizing agent to the third reducing agent can be adjusted according to the carrier and dopant ions to be injected into the organic semiconductor layer precursor.
  • the total content of the third oxidizing agent and the third reducing agent in the dope solution is not particularly limited, but is preferably 0.01 to 1,000 mM from the viewpoint of improving doping efficiency.
  • the third oxidizing agent and the third reducing agent contained in the dope solution are preferably completely dissolved in the solvent water, but a part of them may be contained in the dope solution in a solid state.
  • the dopant ion salt is a coexisting salt of a dopant ion that is ultimately introduced into the organic semiconductor layer and a spectator ion that is a counter ion of the dopant ion.
  • the dopant ion is preferably a closed-shell ion, more preferably a hydrophobic closed-shell ion.
  • the spectator ion is an ion that is not introduced into the organic semiconductor.
  • the dopant ion is preferably a closed shell anion capable of forming a salt with a spectator ion, and more preferably a hydrophobic closed shell anion capable of forming a salt with a spectator ion.
  • dopant ions examples include bis(trifluoromethanesulfonyl)imide ion (TFSI ion), tetrafluoroborate ion (BF 4 ⁇ ), hexafluorophosphate ion (PF 6 ⁇ ), and hexafluoroantimonate ion (SbF 6 ⁇ ) .
  • dopant ions can be introduced into the organic semiconductor layer regardless of the type of dopant ion.
  • the dopant ions may be appropriately selected depending on the properties of the organic semiconductor.
  • the doping ions are preferably anions such as TFSI ions and FAP ions, in which the negative charge is more delocalized.
  • sulfonate ions, sulfate ions, and the like can also be used.
  • the spectator ion is preferably a cation with a closed shell structure capable of forming a salt with the dopant ion.
  • Such spectator ions include, for example, ions of metals such as Li, Na, Cs, Mg, Ca, Cu, and Ag; metal ions of these metals modified with cyclic ethers, etc.; organic molecular ions such as imidazolium, morpholinium, piperidinium, pyridinium, pyrrolidinium, ammonium, and phosphonium; and derivatives of these organic molecular ions.
  • metals such as Li, Na, Cs, Mg, Ca, Cu, and Ag
  • organic molecular ions such as imidazolium, morpholinium, piperidinium, pyridinium, pyrrolidinium, ammonium, and phosphonium
  • the dopant ion is preferably a closed-shell cation capable of forming a salt with a spectator ion, and more preferably a hydrophobic closed-shell cation capable of forming a salt with a spectator ion.
  • the spectator ion is preferably a closed shell anion capable of forming a salt with the dopant ion.
  • Such spectator ions include anions such as BF 4 ⁇ , PF 6 ⁇ , SbF 6 ⁇ , carbonate ion, sulfonate ion, nitrate ion, phosphate ion, thiocyanate ion, cyanate ion, chloride ion, bromide ion, iodide ion, triiodide ion, fluoride ion, FAP ion, TFSI ion, TFESI ion, BOB ion, MOB ion, PFPB ion, TtFPB ion, TFPB ion, and FeCl 4 ⁇ ; and derivatives thereof.
  • anions such as BF 4 ⁇ , PF 6 ⁇ , SbF 6 ⁇ , carbonate ion, sulfonate ion, nitrate ion, phosphate ion, thiocyanate ion,
  • the doping ion salt may be used alone or in any combination of two or more kinds in any ratio.
  • the total content of the salt of the doping ion in the dope solution is not particularly limited, but is preferably 0.01 mM or more and 1,000 mM or less. At least a portion of the salt of the doping ion may be present in the aqueous solution dissolved in the water solvent, or a portion may be present as a solid.
  • the water solvent is not particularly limited, and examples thereof include tap water; pure water such as distilled water, RO water, and deionized water; and ultrapure water having a resistivity of 18 M ⁇ or more; however, pure water is preferred, and deionized water is more preferred.
  • pH of the doping solution is not particularly limited, but since the doping amount of the organic semiconductor depends on the pH of the doping solution, it is preferable to adjust the pH of the doping solution to a desired doping amount. By controlling the doping amount of the organic semiconductor by adjusting the pH of the doping solution, the Fermi level of the organic semiconductor can be precisely controlled.
  • pH refers to the pH at 25°C.
  • the redox potentials of the third oxidizing agent and the third reducing agent can be adjusted to a level at which carrier transfer can occur between the organic semiconductor and the third oxidizing agent and the third reducing agent.
  • the third oxidizing agent and the third reducing agent used in this embodiment are compounds that oxidize and reduce the organic semiconductor by electron transfer or proton-coupled electron transfer, respectively, and the redox potential of such compounds can be precisely and easily adjusted by adjusting the pH of the dope solution.
  • a one-electron oxidizing agent or one-electron reducing agent that does not involve proton transfer is used, the above-mentioned adjustment is difficult.
  • Figure 3 is a plot of the change in the redox potential of benzoquinone/hydroquinone (hereafter referred to as "HQ/BQ") as a function of pH on the equilibrium diagram of the redox potential of water versus pH.
  • HQ/BQ benzoquinone/hydroquinone
  • the redox potential of HQ/BQ can be adjusted within a range that does not involve a reaction with water, so the reactivity can be adjusted appropriately depending on the type of organic semiconductor, etc.
  • the preferred range of pH of the dope solution varies depending on the type of organic semiconductor, the type of third oxidizing agent, the type of third reducing agent, the content of the third oxidizing agent, and the content of the third reducing agent, but can be easily determined by spectroscopic techniques, electrochemical techniques, quantum chemical calculations, and the like. The procedure for setting the preferred range of pH of the dope solution is described below.
  • the redox potential of the third oxidizing agent and the third reducing agent can both be expressed based on the vacuum level or the electrode potential of a reference electrode such as silver-silver chloride.
  • this value for BQ/HQ is publicly known.
  • Doping of the p-type organic semiconductor layer can be achieved by adjusting the relationship between the redox potential of the third oxidant and the ionization potential of the p-type organic semiconductor.
  • the ionization potential of p-type organic semiconductors can be easily measured by photoelectron yield spectroscopy and cyclic voltammetry, and many values measured by similar methods have been reported in the literature, so there are no technical difficulties in measuring and investigating them.
  • the relationship between the redox potential of the third reducing agent and the electron affinity of the n-type organic semiconductor can be adjusted.
  • the electron affinity of n-type organic semiconductors can be estimated from information obtained by combining ionization potential measurements using photoelectron yield spectroscopy with band gap measurements (optical absorption measurements), and can also be evaluated using cyclic voltammetry. This information has also been widely reported in the literature, and there are no technical difficulties in measuring and investigating it.
  • the preferred pH range of the dope solution can be set based on the above method from the redox potential, ionization potential, and electron affinity.
  • the redox potential, ionization potential, and electron affinity may be values estimated by density functional theory calculations.
  • the pH of the dope solution may be adjusted by adding agents such as pH adjusters, such as acids and bases, and pH buffers.
  • agents such as pH adjusters, such as acids and bases, and pH buffers.
  • the method of contacting the dope solution with the surface of the organic semiconductor layer is not particularly limited and can be appropriately selected from any process such as a known solution process or a process similar thereto.
  • known solution processes include a method of immersing the organic semiconductor layer in a surface modification liquid, and a method of applying the dope solution to the organic semiconductor layer by any application method such as a spin coating method, a spray coating method, and a roll coating method.
  • the temperature when the surface of the first electrode is brought into contact with the surface modifying liquid is not particularly limited, but is preferably 5° C. or higher and 50° C. or lower, more preferably 15° C. or higher and 35° C. or lower.
  • the time for which the surface of the first electrode is in contact with the surface modifying liquid is not particularly limited, but is preferably from 1 second to 10 hours.
  • FIGS 1 and 2 show an example in which poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14, also simply referred to as "PBTTT”) is used as the p-type organic semiconductor, and benzoquinone is used as the third oxidant.
  • the aqueous solution contains benzoquinone (BQ), which is the third oxidant, as well as hydroquinone (HQ), which is its redox pair.
  • BQ benzoquinone
  • HQ hydroquinone
  • Figure 1 shows the energy diagram of PBTTT and BQ/HQ.
  • the vertical axis represents energy based on the vacuum level.
  • the redox potential of BQ/HQ can be easily adjusted by adjusting the pH of the aqueous solution, and in relation to PBTTT, it is possible for electron transfer accompanied by proton transfer (ET) to occur.
  • BQ/HQ can act as a third oxidizing agent for PBTTT.
  • dopant ions Y- in the dope solution are introduced from the positively charged surface of the organic semiconductor layer by electrostatic interaction (FIG. 2(B)).
  • a doped layer containing holes and dopant ions Y- is formed in the region including the surface of the PBTTT layer (FIG. 2(C)).
  • the above estimated mechanism relates to the manner in which holes and dopant anions are introduced into a p-type organic semiconductor layer.
  • the estimated doping mechanism is similar when electrons and dopant cations are introduced into an n-type organic semiconductor layer.
  • the organic semiconductor layer precursor to be doped in the doping step will be described.
  • the "organic semiconductor layer precursor to be subjected to doping" is a layer that is directly incorporated into the vertical diode as an "organic semiconductor layer".
  • the "organic semiconductor layer” may be used as a concept including the "organic semiconductor layer precursor”
  • the "organic semiconductor layer precursor” may be used as a concept including the "organic semiconductor layer”.
  • the organic semiconductor layer precursor is a layer formed from an organic semiconductor, and has a single-layer structure or a multilayer structure.
  • the layer structure of the organic semiconductor layer precursor and the type of organic semiconductor constituting the organic semiconductor layer precursor may be appropriately selected depending on the surface modification of the first electrode, the types of carriers and dopant ions injected into the organic semiconductor layer precursor in the doping process, etc.
  • the organic semiconductor layer precursor when a low molecular weight hydrophobic cation is attached to the first electrode, the organic semiconductor layer precursor may be a single-layered n-type organic semiconductor layer precursor; a two-layered organic semiconductor layer precursor in which an n-type organic semiconductor layer and a p-type organic semiconductor layer are laminated from the first electrode to the second electrode; or a three-layered organic semiconductor layer precursor in which an n-type organic semiconductor layer, an i-type organic semiconductor layer, and a p-type organic semiconductor layer are laminated from the first electrode to the second electrode.
  • the layer to be doped is a p-type organic semiconductor layer
  • a suitable organic semiconductor layer precursor may be selected based on the mechanism of the diode, as described above.
  • the organic semiconductor constituting the organic semiconductor layer precursor may be a low molecular weight compound or a high molecular weight compound.
  • Examples of p-type low molecular weight compounds include condensed polycyclic compounds, triarylamine compounds, heterocyclic five-membered compounds, phthalocyanine compounds, porphyrin compounds, carbon nanotubes, and graphene.
  • Fused polycyclic compounds include, for example, anthracene, tetracene, pentacene, anthradithiophene, and hexabenzocoronene. These may have a substituent.
  • triarylamine compounds include 4,4',4"-tris[(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA), 4,4',4"-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD), N,N'-diphenyl-N,N'-di(m-tolyl)benzidine (TPD), 1,3-bis(9-carbazolyl)benzene (mCP), and 4,4'-bis(9-carbazolyl)-2,2'-biphenyl (CBP).
  • m-MTDATA 4,4',4"-tris[(3-methylphenyl)phenylamino]triphenylamine
  • m-MTDATA 4,4',4"
  • heterocyclic 5-membered compounds examples include oligothiophenes and tetrathiafulvalene (TTF). These may have a substituent.
  • Phthalocyanine compounds include metal complexes of phthalocyanine, naphthalocyanine, anthracyanine, and tetrapyrazinoporphyrazine. These may have a substituent.
  • Porphyrin compounds include metal complexes of porphyrin which may have a substituent.
  • Examples of p-type low molecular weight compounds include 3,11-dioctyldinaphtho[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (C 8 -DNBDT), 3,11-didecyldinaphtho[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene (C 10 -DNBDT), 3,9-dihexyldinaphtho[2,3-b;2',3-d]thiophene (C 6 -DNT), 2,9-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (C 10 -DNTT), and 2,7-dioctylbenzothieno[3,2-b][1]benzothiophene (C 8 -BTBT), and 6,13-bis(
  • n-type low molecular weight compounds include fullerene compounds, electron-deficient phthalocyanine compounds, condensed polycyclic compounds (such as naphthalene tetracarbonyl compounds and perylene tetracarbonyl compounds), TCNQ compounds (tetracyanoquinodimethane compounds), and graphene.
  • fullerene compounds include C60 , C70, C76 , C78 , C80 , C82 , C84 , C86 , C88 , C90 , C96 , C116 , C180 , C240 , C540 , and PCBM, and preferably C60 , C70 , C86 , or PCBM . These may have a substituent.
  • the electron-deficient phthalocyanine compound includes metal complexes of phthalocyanine compounds such as phthalocyanine, naphthalocyanine, anthracyanine, and tetrapyrazinoporphyrazine, each of which has four or more electron-withdrawing groups bonded thereto. These may have a substituent.
  • phthalocyanine compounds such as phthalocyanine, naphthalocyanine, anthracyanine, and tetrapyrazinoporphyrazine, each of which has four or more electron-withdrawing groups bonded thereto. These may have a substituent.
  • electron-deficient phthalocyanine compounds include fluorinated phthalocyanine (F 16 MPc) and chlorinated phthalocyanine (Cl 16 MPc), etc.
  • F 16 MPc fluorinated phthalocyanine
  • Cl 16 MPc chlorinated phthalocyanine
  • M is a central metal
  • Pc is phthalocyanine.
  • Naphthalene tetracarbonyl compounds include naphthalene tetracarboxylic anhydride (NTCDA), naphthalene bisimide compounds (NTCDI), and perinone pigments (Pigment Orange 43, Pigment Red 194, etc.).
  • NTCDA naphthalene tetracarboxylic anhydride
  • NTCDI naphthalene bisimide compounds
  • perinone pigments Pigment Orange 43, Pigment Red 194, etc.
  • Perylene tetracarbonyl compounds include perylene tetracarboxylic anhydride (PTCDA), perylene bisimide compounds (PTCDI), and benzimidazole condensed ring compounds (PV). Specific examples of perylene tetracarbonyl compounds include dicyanoperylene-3,4:9,10-bis(dicarboximide).
  • TCNQ compounds include TCNQ, TCNQ, and compounds in which the benzene ring portion of these compounds has been replaced with another aromatic ring or heterocycle.
  • Specific TCNQ compounds include TCNQ (tetracyanoquinodimethane), TCNAQ (tetracyanoanthraquinodimethane), and TCN3T (2,2'-((2E,2"E)-3',4'-alkyl-substituted-5H,5"H-[2,2':5',2"-terthiophene]-5,5"-diyldiene) dimalononitrile derivatives).
  • the polymer compound includes a ⁇ -conjugated polymer.
  • ⁇ -conjugated polymer examples include polythiophene, polyselenophene, polypyrrole, polyparaphenylene, polyparaphenylenevinylene, polythiophenevinylene, and polyaniline, which may have a substituent.
  • n-type polymer compounds include poly ⁇ [N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-o-5,5'-(2,2'-bithiophene) ⁇ (N2200) and poly ⁇ [N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene) ⁇ (P(NDI2OD-T2)).
  • the organic semiconductor may be used alone or in any combination of two or more kinds in any ratio.
  • the organic semiconductor may be crystallized.
  • the organic semiconductor when the organic semiconductor is a low molecular weight compound, it is preferable that the organic semiconductor is a single crystal.
  • the organic semiconductor when the organic semiconductor is a high molecular weight compound, the high molecular weight compound may be molecular oriented.
  • the method for producing the organic semiconductor layer precursor is not particularly limited, and any method such as a publicly known method or a method similar thereto can be used.
  • An example of a publicly known method is a method in which a composition layer is formed by a coating method using a composition containing an organic semiconductor and a solvent, and the solvent is removed from the composition layer to obtain the organic semiconductor layer precursor.
  • the organic semiconductor layer precursor has a multilayer structure, the organic semiconductor layer precursor can be produced by repeating the cycle of forming the above-mentioned composition layer and removing the solvent from the composition layer multiple times.
  • the solvent contained in the composition is not particularly limited as long as it can dissolve the organic semiconductor, and examples thereof include aromatic organic solvents such as dichlorobenzene; acetonitrile; butyl acetate; and fluoroalcohols.
  • the content of the organic semiconductor in the composition may be appropriately adjusted depending on the intended thickness of the organic semiconductor layer precursor, and is preferably 0.1% by mass or more and 99% by mass or less.
  • the thickness of the organic semiconductor layer precursor (total thickness when the organic semiconductor layer precursor has a multi-layer structure) is not particularly limited and may be appropriately adjusted taking into consideration the use of the vertical diode and the element life, etc.
  • Specific examples of the thickness of the organic semiconductor layer precursor include 11 nm to 300 nm, preferably 12 nm to 70 nm, more preferably 15 nm to 50 nm, even more preferably 18 nm to 40 nm, and particularly preferably 20 nm to 30 nm.
  • the "organic semiconductor layer precursor" referred to here is a layer that is incorporated into the vertical diode as an "organic semiconductor layer” either doped or as is, and therefore the total thickness of the organic semiconductor is as described above.
  • the ion layer that contributes to improving the rectification characteristics is not dispersed in the organic semiconductor layer, but exists at the interface between the first electrode and the organic semiconductor layer, so that a high rectification ratio can be achieved even if the organic semiconductor layer is thin, regardless of the presence or absence of a doped layer. More specifically, while the typical thickness of the organic semiconductor layer in a conventional vertical diode is about 100 nm, in the example described below, a vertical diode that exhibits good rectification characteristics is obtained even though the organic semiconductor layer is 25 nm thick.
  • the first electrode, the organic semiconductor layer, and the second electrode are laminated adjacent to each other in this order. At this time, the first electrode and the organic semiconductor layer are laminated so that the surface of the first electrode modified in the electrode modification step and the organic semiconductor layer are in contact with each other. Furthermore, in the case where a doped layer is formed in the organic semiconductor layer by the doping step, the organic semiconductor layer and the second electrode are laminated so that the doped layer and the second electrode are in contact with each other.
  • the method for stacking each layer is not particularly limited, so long as the layers are stacked in an order that satisfies the above-mentioned conditions, and any method, such as a publicly known method or a method similar thereto, may be used.
  • the lamination may be performed by preparing a first electrode, modifying the surface of the first electrode, preparing an organic semiconductor layer on the surface-modified first electrode, and preparing a second electrode on the organic semiconductor layer, or by preparing a second electrode, preparing an organic semiconductor layer on the second electrode, and disposing the surface-modified first electrode on the organic semiconductor layer.
  • methods for preparing an organic semiconductor layer include the wet method described above in [1-2-4. Organic semiconductor layer precursor and organic semiconductor layer].
  • the lamination of the organic semiconductor layer may also be performed by a transfer method in which an organic semiconductor layer is prepared on a transfer substrate, the organic semiconductor layer is transferred onto one of the first and second electrodes whose surfaces are modified, and the other electrode is prepared on the organic semiconductor layer.
  • the lamination may be performed, for example, by preparing a first electrode, modifying the surface of the first electrode, preparing an organic semiconductor layer precursor on the surface-modified first electrode, subjecting the organic semiconductor layer precursor to a doping step, and preparing a second electrode on the doped layer formed by the doping step, or by preparing a second electrode, transferring the organic semiconductor layer on which the doped layer has been formed by the doping step from a transfer substrate to the second electrode, and arranging the surface-modified first electrode on the undoped layer of the organic semiconductor layer.
  • the material of the second electrode to be laminated together with the organic semiconductor layer and the method for producing the second electrode will be described below.
  • the second electrode is an anode when the first electrode is a cathode, and is a cathode when the first electrode is an anode.
  • the second electrode when the second electrode is an anode, it is desirable that the second electrode exhibit a work function larger than the organic semiconductor constituting the organic semiconductor layer and the first electrode. Also, when the second electrode is a cathode, it is desirable that the second electrode has a work function smaller than the LUMO of the organic semiconductor and smaller than the first electrode.
  • the material constituting the second electrode is not particularly limited, and may be appropriately selected from conductive materials depending on the type of the first electrode and organic semiconductor. Specific electrode materials include those exemplified as materials constituting the unmodified first electrode.
  • the thickness of the second electrode is not particularly limited and may be adjusted appropriately taking into consideration the application of the vertical diode and the element life, etc. Specific examples of the thickness of the second electrode include 10 nm or more and 200 nm or less, and preferably 20 nm or more and 50 nm or less.
  • the second electrode is fabricated to a predetermined thickness by any method, such as a known method or a method similar thereto, and is laminated with the other layers.
  • Known methods for fabricating the second electrode include, for example, vacuum deposition, sputtering, chemical vapor deposition, and plating.
  • the substrate is not particularly limited as long as it is capable of forming the first electrode or the second electrode, but it is preferable that it does not chemically react with the organic semiconductor that constitutes the organic semiconductor layer.
  • Examples of such substrates include glass substrates and silicon substrates.
  • the manufacturing method according to this embodiment may include steps other than the steps described above. Examples of other steps include a step of washing the first electrode whose surface has been modified after the electrode modification step; and a step of washing the doped organic semiconductor layer after the doping step.
  • the manufacturing method according to this embodiment may include, in addition to or instead of the doping step, a step of doping the organic semiconductor layer by any method, such as a known method as disclosed in WO 2020/085342 or a method equivalent thereto.
  • the second embodiment of the present disclosure is a vertical diode in which a first electrode, an organic semiconductor layer, and a second electrode are stacked adjacent to each other in this order, and low-molecular-weight hydrophobic ions are attached to a surface of the first electrode that is adjacent to the organic semiconductor layer.
  • the vertical diode according to this embodiment can be manufactured by the manufacturing method according to the first embodiment.
  • the vertical diode according to this embodiment has excellent rectification characteristics and can therefore be suitably used as a rectifier diode.
  • the vertical diode 10 is a vertical diode in which a first electrode 12, an organic semiconductor layer 14, and a second electrode 18 are stacked adjacent to each other in this order.
  • Low-molecular-weight hydrophobic ions 13 are attached to the surface of the first electrode 12 that is adjacent to the organic semiconductor layer 14.
  • the low molecular weight hydrophobic ions are electrostatically attached to the surface of the first electrode by the electrode modification step in the first embodiment. That is, the low molecular weight hydrophobic ions are any of low molecular weight hydrophobic cations and/or other low molecular weight hydrophobic cations derived from the first reducing agent contained in the surface modification liquid (S1); low molecular weight hydrophobic anions and/or other low molecular weight hydrophobic anions derived from the first oxidizing agent contained in the surface modification liquid (S2); low molecular weight hydrophobic closed shell cations contained in the surface modification liquid (S3); and low molecular weight hydrophobic closed shell anions contained in the surface modification liquid (S4). Therefore, for low molecular weight hydrophobic ions, the explanation in the section [1-1-1. Surface modification liquid] is incorporated herein by reference.
  • the coverage of the low molecular weight hydrophobic ions is preferably 10 area % or more and 50 area % or less, more preferably 15 area % or more and 40 area % or less, and even more preferably 20 area % or more and 30 area % or less.
  • the molecular hydrophobic ions attached to the surface of the first electrode may diffuse into the organic semiconductor layer during the process of manufacturing the vertical diode or during storage of the vertical diode.
  • the preferred range of the coverage rate of the low molecular hydrophobic ions is as described above, both immediately after the surface modification of the first electrode and after the vertical diode is manufactured.
  • the coverage rate of low molecular weight hydrophobic ions can be measured by X-ray photoelectron spectroscopy (XPS).
  • XPS X-ray photoelectron spectroscopy
  • low-molecular-weight hydrophobic ions do not form salts with any of the counter ions, including ions derived from the organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, and ions of the metal contained in the first electrode.
  • the proportion of low molecular weight hydrophobic ions forming salts with counter ions is preferably 0 mol% or more and 25 mol% or less, more preferably more than 0 mol% and 20 mol% or less, even more preferably 0 mol% or more and 15 mol% or less, and particularly preferably 5 mol% or more and 10 mol% or less.
  • the proportion of low molecular weight hydrophobic ions that form salts with counterions on the surface of the first electrode can be measured by X-ray photoelectron spectroscopy (XPS).
  • XPS X-ray photoelectron spectroscopy
  • the organic semiconductor layer 14 preferably has a doped layer 17 and an undoped layer 15.
  • the doped layer 17 is a layer formed as the outermost layer of the organic semiconductor layer 14, and is adjacent to the second electrode 18.
  • This doped layer 17 is a layer formed by injecting carriers (electrons or holes) and dopant ions into the organic semiconductor layer precursor in the doping step in the first embodiment.
  • the organic semiconductor layer preferably comprises a doped layer and an undoped layer.
  • the undoped layer may have a single layer structure or a multilayer structure.
  • the dopant ions contained in the doped layer are derived from salts of the dopant ions contained in the dope solution and have the opposite polarity to the carriers. Therefore, when the carriers contained in the doped layer are holes, the dopant ions contained in the doped layer are dopant anions.
  • the low molecular weight hydrophobic ions modifying the surface of the first electrode are low molecular weight hydrophobic cations, in terms of improving the rectification characteristics of the vertical diode and improving the current density at low voltage.
  • the dopant ions contained in the doped layer are dopant cations.
  • the organic semiconductor layer has such a doped layer, it is preferable that the low molecular weight hydrophobic ions modifying the surface of the first electrode are low molecular weight hydrophobic anions, in terms of improving the rectification characteristics of the vertical diode and improving the current density at low voltage.
  • a layer of a hole-transporting organic semiconductor i.e., a layer of a p-type organic semiconductor
  • holes and dopant anions are injected into the doped layer, so that a vertical diode with excellent rectification characteristics and high current density at low voltage can be obtained.
  • a layer of an electron-transporting organic semiconductor i.e., a layer of an n-type organic semiconductor
  • electrons and dopant cations are injected into the doped layer, so that a vertical diode with excellent rectification characteristics and high current density at low voltage can be obtained.
  • the proportion of dopant ions that form salts with counterions can be measured by X-ray photoelectron spectroscopy (XPS).
  • a region from the surface of the organic semiconductor layer precursor in contact with the dope solution to the depth reached by the carriers and dopant ions becomes a doped layer, and the remaining region becomes an undoped layer.
  • the depth reached by the carriers and dopant ions usually corresponds to the thickness Td of the doped layer.
  • the thickness Td of the doped layer is not particularly limited, but is preferably 1 nm or more and 100 nm or less, more preferably 2 nm or more and 20 nm or less, even more preferably 3 nm or more and 15 nm or less, and even more preferably 4 nm or more and 10 nm or less.
  • the thickness Tu of the undoped layer obtained by subtracting the thickness Td of the doped layer from the total thickness To of the organic semiconductor layer is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 50 nm or less, even more preferably 12 nm or more and 30 nm or less, and even more preferably 15 nm or more and 25 nm or less.
  • the thickness of the undoped layer Tu can be estimated by capacitance measurement, and if the thickness of the undoped layer Tu can be determined by a contact step gauge, the thickness of the doped layer can also be estimated.
  • the undoped layer is a layer into which carriers and dopant ions are not injected in the doping process in the first embodiment.
  • dopant ions in the doped layer may diffuse into the region during the manufacturing process after the doping process and during storage of the vertical diode, in this disclosure, the layer that acts as a resistive component in capacitance measurement is called the "doped layer” and the layer that acts as a capacitive component is called the "undoped layer.”
  • the undoped layer 15 is illustrated as a single layer in FIG. 4(B), the undoped layer may have a multi-layer structure.
  • the vertical diode of this embodiment can efficiently convert high-frequency AC power into DC power.
  • "high frequency” means a frequency of 10 MHz or higher (e.g., 10 MHz, 100 MHz, or 1 GHz).
  • the vertical diode according to this embodiment has a conversion efficiency (AC-DC conversion efficiency) for converting 10 MHz AC power into DC power of preferably 4% or more, more preferably 5% or more, and even more preferably more than 5%.
  • the vertical diode according to this embodiment preferably has a conversion efficiency for converting 1 GMz AC power to DC power (AC-DC conversion efficiency) of 4% or more, more preferably 5% or more, and even more preferably more than 5%.
  • the layer structures shown in (A1) to (A5) below are preferred.
  • the first electrode or the second electrode is usually formed on a substrate 11, as shown in Figures 4(A) and 4(B).
  • the layer structures shown in (A6) to (A10) below are preferred.
  • the first electrode or the second electrode is usually formed on a substrate.
  • A6 First electrode/p-type organic semiconductor layer/second electrode
  • A7 First electrode/p-type organic semiconductor layer/n-type organic semiconductor layer/second electrode
  • A8) First electrode/p-type organic semiconductor layer/n-type organic semiconductor layer (doped layer)/second electrode
  • A9 First electrode/p-type organic semiconductor layer/i-type organic semiconductor layer/n-type organic semiconductor layer/second electrode
  • A10 First electrode/p-type organic semiconductor layer/i-type organic semiconductor layer/n-type organic semiconductor layer (doped layer)/second electrode
  • p-type organic semiconductor layer (doped layer) means that the p-type organic semiconductor layer is a doped layer containing holes and dopant anions, or one of the outermost layers of the p-type organic semiconductor layer is a doped layer containing holes and dopant anions, and is adjacent to two electrodes.
  • n-type organic semiconductor layer (doped layer) means that the n-type organic semiconductor layer is a doped layer containing electrons and dopant cations, or one of the outermost layers of the n-type organic semiconductor layer is a doped layer containing electrons and dopant cations, and is adjacent to two electrodes.
  • a third embodiment of the present disclosure is a manufacturing method for a vertical diode in which a first electrode, an organic semiconductor layer having a doped layer and an undoped layer, and a second electrode are stacked adjacent to each other in this order, and the doped layer is stacked adjacent to the first electrode or the second electrode, and includes a doping step of forming the doped layer by contacting a surface of an organic semiconductor layer precursor with an aqueous solution containing a fourth oxidizing agent or a fourth reducing agent and a salt of a dopant ion (hereinafter, sometimes referred to as a "dope solution").
  • a doped layer in which carriers and dopant ions are injected is formed near the first electrode or the second electrode. This improves carrier injection from the electrode adjacent to the doped layer to the organic semiconductor layer, making it possible to obtain a vertical diode that exhibits excellent rectification characteristics. Therefore, the manufacturing method according to this embodiment is useful as a method for manufacturing a rectifier diode. Furthermore, according to a preferred aspect of this embodiment, it is possible to obtain a vertical diode that has excellent high-frequency response or that exhibits high current density even at a low voltage.
  • the doping step is a step of forming a doped layer as the outermost layer of the organic semiconductor layer, and is one step of a step of producing an organic semiconductor layer having a doped layer and an undoped layer (hereinafter, sometimes referred to as an "organic semiconductor layer producing step").
  • the organic semiconductor layer is composed of a doped layer and an undoped layer.
  • the undoped layer may have a single layer structure or a multilayer structure.
  • the organic semiconductor layer preparation process is a process A in which an organic semiconductor layer precursor is subjected to a doping process, and carrier and dopant ions are injected into a region from the surface of the organic semiconductor layer precursor to a desired depth, thereby obtaining an organic semiconductor layer having a doped layer and an undoped layer; or a process B in which an organic semiconductor layer precursor is subjected to a doping process, and carrier and dopant ions are injected into the entire organic semiconductor layer precursor to form a doped layer, and an undoped organic semiconductor layer is laminated on the obtained doped layer, thereby obtaining an organic semiconductor layer.
  • step A is the same process as the doping step in the first embodiment, and the preferred aspects are also the same, so the explanation in section [1-2. Doping step] is incorporated herein by reference. In this case, in section [1-2. Doping step], the third oxidizing agent and the third reducing agent are to be read as the fourth oxidizing agent and the fourth reducing agent, respectively.
  • step A the region of the organic semiconductor layer precursor from the surface of the organic semiconductor layer precursor in contact with the dope solution to the depth reached by the carriers and dopant ions usually becomes a doped layer, and the remaining region becomes an undoped layer.
  • the "desired depth" to which the carriers and dopant ions are injected usually corresponds to the thickness Td of the doped layer described later.
  • the doping step in step B is the same process as the doping step in the first embodiment, except that carrier and dopant ions are injected into the entire organic semiconductor layer precursor, not just a portion of it. Therefore, the explanation in section [1-2. Doping step] is incorporated herein, and the method for injecting carrier and dopant ions into the entire organic semiconductor layer precursor is as described below. Note that in section [1-2. Doping step], the third oxidizing agent and the third reducing agent should be read as the fourth oxidizing agent and the fourth reducing agent, respectively.
  • Injection of carriers and dopant ions into the entire organic semiconductor layer precursor can be achieved by setting the thickness of the organic semiconductor layer precursor to a thickness equivalent to the doped layer, but it can be achieved more efficiently by combining one or more of the following: adjustment of the total content of the fourth oxidizing agent or the fourth reducing agent in the dope solution; adjustment of the contact temperature between the organic semiconductor layer precursor and the dope solution; and adjustment of the contact time between the organic semiconductor layer precursor and the dope solution. It is preferable to adjust these conditions within the ranges described in [1-2. Doping process].
  • the organic semiconductor layer precursor and the undoped layer can be prepared by any method, such as a known method or a method similar thereto.
  • Known methods include, for example, the wet method described above in the section [1-2-4. Organic semiconductor layer precursor and organic semiconductor layer].
  • the organic semiconductor layer precursor is prepared directly on the first electrode or the second electrode and then subjected to the doping step.
  • the manufacturing method preferably includes an electrode modification step of modifying the surface of the first electrode by bringing the surface of the first electrode into contact with a surface modification liquid.
  • the surface modification liquid used in the electrode modification step is any one of the surface modification liquids (S1) to (S4).
  • S1 A surface modifying solution containing a first reducing agent that reduces a first electrode and produces low-molecular-weight hydrophobic cations.
  • S2 A surface modifying solution containing a first oxidizing agent that oxidizes the first electrode and generates a low-molecular-weight hydrophobic anion.
  • the electrode modification process in this embodiment is the same process as the electrode modification process in the first embodiment, and the preferred aspects are also the same. Therefore, the explanation in the section [1-1. Electrode modification process] is incorporated herein by reference.
  • the doped layer is formed using a doping solution containing a fourth oxidizing agent and a salt of a dopant anion in the doping step
  • a vertical diode having a doped layer in which holes and dopant anions are injected near the second electrode is obtained. Therefore, in the electrode modification step, it is preferable to use the surface modification liquid (S1) or (S3) to prepare a first electrode in which electrons are injected and low-molecular-weight hydrophobic cations are electrostatically attached to the surface. This improves not only the hole injection from the second electrode to the organic semiconductor layer but also the electron injection from the first electrode to the organic semiconductor layer, and can improve the rectification characteristics of the vertical diode and the current density at low voltage.
  • the doping step when a dope layer is formed using a dope solution containing a fourth reducing agent and a salt of a dopant cation, a vertical diode having a dope layer in which electrons and dopant cations are injected near the second electrode is obtained. Therefore, in the electrode modification step, it is preferable to use the surface modification liquid (S2) or (S4) to prepare a first electrode into which holes are injected and in which hydrophobic closed-shell anions are electrostatically attached to the surface. This is because not only the electron injection from the second electrode to the organic semiconductor layer but also the hole injection from the first electrode to the organic semiconductor layer is improved, and the rectification characteristics of the vertical diode and the current density at low voltage can be improved.
  • S2 surface modification liquid
  • S4 hydrophobic closed-shell anions
  • the first electrode, the organic semiconductor layer having a doped layer and an undoped layer, and the second electrode are laminated adjacent to each other in this order, so that the organic semiconductor layer and the first electrode or the second electrode are laminated such that the doped layer is in contact with the first electrode or the second electrode. Furthermore, when the surface of the first electrode is modified by the electrode modification step, the first electrode and the organic semiconductor layer are laminated so that the modified surface of the first electrode and the organic semiconductor layer are in contact with each other.
  • the method for stacking each layer is not particularly limited, so long as the layers are stacked in an order that satisfies the above-mentioned conditions, and any method, such as a publicly known method or a method similar thereto, may be used.
  • the lamination may be performed by preparing a first electrode, preparing an organic semiconductor layer precursor on the first electrode, subjecting the organic semiconductor layer precursor to a doping step, and preparing a second electrode on the doped layer formed by the doping step, or by preparing a second electrode, preparing an organic semiconductor layer precursor on the second electrode, subjecting the organic semiconductor layer precursor to a doping step, and preparing a first electrode on the doped layer formed by the doping step.
  • the layers may be laminated by a transfer method in which an organic semiconductor layer is prepared on a transfer substrate by an organic semiconductor layer preparation step, the organic semiconductor layer is transferred onto one of the first and second electrodes, and the other electrode is prepared on the organic semiconductor layer.
  • the lamination may be performed by preparing a first electrode, preparing an organic semiconductor layer precursor on the first electrode, subjecting the organic semiconductor layer precursor to a doping process, preparing an undoped layer on the doped layer formed by the doping process, and preparing a second electrode on the undoped layer, or the lamination may be performed by preparing a second electrode, preparing an organic semiconductor layer precursor on the second electrode, subjecting the organic semiconductor layer precursor to a doping process, preparing an undoped layer on the doped layer formed by the doping process, and preparing a second electrode on the undoped layer.
  • the organic semiconductor layer may be laminated on the first electrode and the second electrode by a transfer method as described above, but from the viewpoint of ensuring the adhesion between the organic semiconductor layer and the first electrode or the second electrode, it is preferable to form an organic semiconductor layer precursor directly on the first electrode or the second electrode, and then subject the organic semiconductor layer precursor to a doping process to laminate on the electrodes.
  • the first electrode and the second electrode are a pair of electrodes. That is, when the first electrode is a cathode, the second electrode is an anode, and when the first electrode is an anode, the second electrode is a cathode.
  • the cathode In order to obtain good rectification characteristics in a vertical diode, it is generally desirable for the cathode to have a work function smaller than the LUMO of the organic semiconductor that constitutes the adjacent organic semiconductor layer, and smaller than the anode. It is also desirable for the anode to have a work function larger than the LUMO of the organic semiconductor.
  • the materials constituting the first electrode and the second electrode are appropriately selected from conductive materials depending on the work function of the paired electrode and the work function of the LUMO of the organic semiconductor.
  • the manufacturing method according to this embodiment includes an electrode modification step, the work function of the first electrode after the first electrode surface modification is used as the work function of the first electrode to be considered for selecting the electrode material.
  • materials constituting the first electrode and the second electrode include metals such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, magnesium, molybdenum, and tungsten; alloys containing two or more of these metals; and metal oxides such as indium oxide, tin oxide, zinc oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); with gold being preferred.
  • metals such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, magnesium, molybdenum, and tungsten
  • alloys containing two or more of these metals such as indium oxide, tin oxide, zinc oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); with gold being preferred.
  • the first electrode and the second electrode are fabricated to a predetermined thickness by any method, such as a known method or a method similar thereto, and are laminated with other layers.
  • Known methods for fabricating the first electrode and the second electrode include, for example, vacuum deposition, sputtering, chemical vapor deposition, and plating.
  • the thickness of the first electrode and the second electrode is not particularly limited and may be adjusted appropriately taking into consideration the application of the vertical diode and the element life, etc. Specific thicknesses of these electrodes are, for example, 10 nm or more and 200 nm or less, and preferably 20 nm or more and 50 nm or less.
  • the first electrode is preferably formed on a substrate, and the same is true when another layer is laminated on the second electrode.
  • the substrate is not particularly limited as long as the first electrode or the second electrode can be formed thereon, but it is preferable that the substrate does not chemically react with the organic semiconductor constituting the organic semiconductor layer. Examples of such substrates include a glass substrate and a silicon substrate.
  • the manufacturing method according to this embodiment may include steps other than the steps described above. Examples of other steps include a step of washing the organic semiconductor layer after the doping step; and a step of washing the first electrode whose surface has been modified.
  • a fourth embodiment of the present disclosure is a vertical diode in which a first electrode, an organic semiconductor layer having a doped layer and an undoped layer, and a second electrode are stacked adjacent to each other in this order, and the doped layer is adjacent to the first electrode or the second electrode.
  • the doped layer includes carriers and dopant ions, and the dopant ions are hydrophobic closed shell ions.
  • the vertical diode according to this embodiment can be manufactured by the manufacturing method according to the third embodiment.
  • the vertical diode according to this embodiment has excellent rectification characteristics and can therefore be suitably used as a rectifier diode.
  • the vertical diode 20 is a vertical diode 20 in which a first electrode 22, an organic semiconductor layer 24 having a doped layer 27 and an undoped layer 25, and a second electrode 28 are stacked adjacent to each other in this order, with the doped layer 27 adjacent to the first electrode 22 or the second electrode 28.
  • the doped layer 27 contains carriers (electrons or holes) and dopant ions.
  • the dopant ions are preferably closed-shell ions, and more preferably hydrophobic closed-shell ions.
  • the doped layer is a layer formed by the doping process in the third embodiment.
  • the dopant ions contained in the doped layer are derived from a salt of the dopant ions contained in the dope solution, and have the opposite polarity to the carriers.
  • holes and dopant anions are injected into the doped layer adjacent to one electrode, improving hole injection from the electrode adjacent to the doped layer to the organic semiconductor layer.
  • electrons and dopant cations are injected into the doped layer adjacent to one electrode, improving electron injection from the electrode adjacent to the doped layer to the organic semiconductor layer.
  • the vertical diode according to this embodiment exhibits good rectification characteristics due to the formation of such a doped layer near one of the electrodes. Furthermore, according to a preferred aspect of this embodiment, a vertical diode with excellent high-frequency response or a vertical diode that exhibits high current density even at low voltage can be obtained. Therefore, the vertical diode according to this embodiment is considered to be applicable to various devices having a diode structure, such as solar cells and light-emitting diodes, and is also expected to be used in wireless communication electronic tags and the like that require high-frequency response.
  • the dopant ions contained in the doped layer preferably do not form salts with counter ions, and more preferably do not form salts with any counter ions other than ions derived from the organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, ions of the metal contained in the first electrode, and ions of the metal contained in the second electrode.
  • the ratio of dopant ions contained in the doped layer that form salts with counter ions other than ions derived from the organic semiconductor constituting the organic semiconductor layer, protons, hydroxide ions, ions of the metal contained in the first electrode, or ions of the metal contained in the second electrode is preferably 0 mol% or more and 25 mol% or less, more preferably more than 0 mol% and 20 mol% or less, even more preferably 0 mol% or more and 15 mol% or less, and particularly preferably 5 mol% or more and 10 mol% or less.
  • the proportion of dopant ions that form salts with counterions can be measured by X-ray photoelectron spectroscopy (XPS).
  • a layer of a hole-transporting organic semiconductor i.e., a layer of a p-type organic semiconductor
  • holes and dopant anions are injected into the doped layer, so that a vertical diode with excellent rectification characteristics and high current density at low voltage can be obtained.
  • a layer of an electron-transporting organic semiconductor i.e., a layer of an n-type organic semiconductor
  • electrons and dopant cations are injected into the doped layer, so that a vertical diode with excellent rectification characteristics and high current density at low voltage can be obtained.
  • the organic semiconductor constituting the doped layer is the same compound as the organic semiconductor constituting the undoped layer. This is because the doped layer and the undoped layer are composed of the same organic semiconductor, which can improve carrier injection from the doped layer to the undoped layer.
  • the thickness Td of the doped layer is not particularly limited, but is preferably 1 nm or more and 100 nm or less, more preferably 2 nm or more and 20 nm or less, even more preferably 3 nm or more and 15 nm or less, and even more preferably 4 nm or more and 10 nm or less.
  • the thickness Tu of the undoped layer obtained by subtracting the thickness Td of the doped layer from the total thickness To of the organic semiconductor layer is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 50 nm or less, even more preferably 12 nm or more and 30 nm or less, and even more preferably 15 nm or more and 25 nm or less.
  • the thickness of the undoped layer Tu can be estimated by capacitance measurement, and if the thickness of the undoped layer Tu can be measured by a contact step gauge, the thickness of the doped layer can also be estimated.
  • the undoped layer is a layer into which carriers and dopant ions are not injected in the doping process in the third embodiment.
  • dopant ions in the doped layer may diffuse into the region during the manufacturing process after the doping process and during storage of the vertical diode, in this disclosure, the layer that acts as a resistive component in capacitance measurement is called the "doped layer” and the layer that acts as a capacitive component is called the "undoped layer.”
  • the undoped layer 25 is illustrated as a single layer, but the undoped layer may have a multi-layer structure.
  • the doped layer 27 is a layer adjacent to the second electrode 28, it is preferable that the low molecular weight hydrophobic ions 23 are attached to the surface of the first electrode that is adjacent to the organic semiconductor layer 24.
  • the low molecular weight hydrophobic ions are ions that are electrostatically attached to the surface of the first electrode adjacent to the organic semiconductor layer by the electrode modification step in the third embodiment.
  • the types of low molecular weight hydrophobic ions, the coverage rate of low molecular weight hydrophobic ions, and the proportion of low molecular weight hydrophobic ions that form salts with counter ions in this embodiment are the same as those of the low molecular weight hydrophobic ions attached to the first electrode in the first embodiment, including their preferred aspects.
  • the low molecular weight hydrophobic ions electrostatically attached to the surface of the first electrode are low molecular weight hydrophobic cations, i.e., electrons have been injected into the first electrode by the electrode modification process.
  • This improves the hole injection from the second electrode to the organic semiconductor layer and also improves the electron injection from the first electrode to the organic semiconductor layer, making it easier for a forward current (current flowing from the second electrode to the first electrode) to flow, and greatly improving the rectification characteristics and current density at low voltage.
  • the layer of the organic semiconductor layer adjacent to the first electrode is an n-type organic semiconductor layer.
  • the low molecular weight hydrophobic ions electrostatically attached to the surface of the first electrode are low molecular weight hydrophobic anions, that is, holes are injected into the first electrode by the electrode modification process. This improves the electron injection from the second electrode to the organic semiconductor layer and also improves the hole injection from the first electrode to the organic semiconductor layer, making it easier for a forward current (current flowing from the first electrode to the second electrode) to flow, and greatly improving the rectification characteristics and current density at low voltage.
  • the layer of the organic semiconductor layer adjacent to the first electrode is a p-type organic semiconductor layer.
  • the layer structure of the vertical diode according to this embodiment are preferably the layer structures shown in (B1) to (B12) below.
  • the first electrode or the second electrode is usually formed on a substrate.
  • (doped layer) n-type organic semiconductor layer means that a doped layer into which electrons and dopant cations are injected is disposed at a position adjacent to the first electrode of the n-type organic semiconductor layer, or that the entire n-type organic semiconductor layer is a doped layer into which electrons and dopant cations are injected.
  • (doped layer) p-type organic semiconductor layer means that a doped layer injected with holes and dopant anions is disposed in a position adjacent to the first electrode of the p-type organic semiconductor layer, or that the entire p-type organic semiconductor layer is a doped layer injected with holes and dopant anions.
  • n-type organic semiconductor layer doped layer
  • a doped layer into which electrons and dopant cations are injected is disposed at a position adjacent to the second electrode of the n-type organic semiconductor layer, or that the entire n-type organic semiconductor layer is a doped layer into which electrons and dopant cations are injected.
  • p-type organic semiconductor layer doped layer
  • p-type organic semiconductor layer means that a doped layer into which holes and dopant anions are injected is disposed at a position adjacent to the second electrode of the p-type organic semiconductor layer, or that the entire p-type organic semiconductor layer is a doped layer into which holes and dopant anions are injected.
  • a low-molecular-weight hydrophobic anion is attached to the surface of the first electrode that is adjacent to the p-type organic semiconductor layer.
  • a low-molecular-weight hydrophobic cation is attached to the surface of the first electrode that is adjacent to the n-type organic semiconductor layer.
  • Example 1 A vertical diode having a layer structure of surface-modified Au electrode/P(NDI-2T)/Au electrode was fabricated by the following procedure. The current-voltage characteristics of the obtained vertical diode are shown in FIG.
  • Au film was formed on a glass substrate by resistance heating deposition to obtain an Au electrode.
  • Au electrodes were immersed in an aqueous solution containing TPPA-OH (1 mM), fructose (1 M), and riboflavin (50 mM).
  • the Au electrode was washed with pure water to obtain a surface-modified Au electrode.
  • a solution containing N2200 (P(NDI-2T)) at a concentration of 1 wt % was spin-coated onto the surface-modified Au electrode at 2,000 rpm for 60 seconds.
  • the coating was baked at 80° C. for 20 minutes to form an organic semiconductor layer with a thickness of about 70 nm.
  • a Au top electrode (30 nm) was evaporated onto the organic semiconductor layer to obtain a vertical diode.
  • Example 2 A surface-modified Cu electrode was prepared by the following procedure.
  • a Cu film was formed on a glass substrate by vacuum resistance heating deposition to obtain a Cu electrode.
  • a Cu electrode was immersed for 30 seconds in an aqueous solution containing BQ (20 mM), Li-TFPB (5 mM), and H 2 SO 4 (1 mM).
  • the Cu electrode was washed with pure water and dried by nitrogen blowing to obtain a surface-modified Cu electrode.
  • UPS Ultraviolet photoelectron spectroscopy
  • Comparative Example 1 An unmodified Cu electrode was obtained according to the procedure (1) of Example 2.
  • ultraviolet photoelectron spectroscopy (UPS) was performed using a 21.2 eV helium light source.
  • the UPS measurement results for the unmodified Cu electrode are shown in FIG. 11(A).
  • an enlarged view of the high binding energy region is shown in FIG. 11(B). From the rising position and the light source energy (21.2 eV), the unmodified Cu electrode was evaluated to have a work function of 4.66 eV, and the unmodified Cu electrode was evaluated to have a work function of 4.66 eV.
  • Example 3 A vertical diode having a layer structure of surface-modified Au electrode/PTAA/Au electrode was fabricated as the first electrode by the following procedure using an Au electrode whose surface had been modified under the same conditions as in Example 2. The current-voltage characteristics of the obtained vertical diode are shown in FIG.
  • PTAA was dissolved in o-dichlorobenzene to prepare a 2 wt % PTAA solution, which was then spin-coated onto the surface-modified Au electrode at 2,000 rpm for 60 seconds.
  • the coating film was dried on a hot plate at 80° C. for 20 minutes to form an organic semiconductor layer.
  • a film of Au was formed on the organic semiconductor layer by vacuum resistance heating deposition to obtain a vertical diode.
  • Example 4 A vertical diode having a layer structure of a surface-modified Cu electrode/PTAA/Au electrode was fabricated in the same manner as in Example 3, except that the surface-modified Cu electrode prepared in Example 2 was used as the first electrode. The current-voltage characteristics of the obtained vertical diode are shown in FIG.
  • Example 5 A vertical diode having a layer structure of a surface-modified Cu electrode/PTAA/Cu electrode was fabricated in the same manner as in Example 4, except that in (3), Cu was deposited by vacuum resistance heating deposition. The current-voltage characteristics of the obtained vertical diode are shown in FIG.
  • Example 6 A vertical diode having a layer structure of a surface-modified Au bilayer electrode/P(NDI-2T)/Au electrode was fabricated by the following procedure. The current-voltage characteristics of the obtained vertical diode are shown in FIG.
  • the coating was dried on a hot plate at 80° C. for 5 minutes.
  • a butyl acetate solvent was dropped onto the Au bilayer electrode, and the glass substrate was rotated at 2,000 rpm for 20 seconds using a spin coater to clean the surface of the Au bilayer electrode.
  • the electrode was dried on a hot plate at 80° C. for 5 minutes to obtain a surface-modified electrode.
  • P(NDI-2T) was dissolved in o-dichlorobenzene to obtain a 1 wt % P(NDI-2T) solution, which was then spin-coated onto the surface-modified electrode at 2,000 rpm for 60 seconds.
  • the coating was dried on a hot plate at 80° C. for 20 minutes to form an organic semiconductor layer with a thickness of approximately 70 nm.
  • a 30 nm thick Au film was formed on the organic semiconductor layer by vacuum resistance heating deposition to obtain a vertical diode.
  • Fig. 8 shows a graph plotting the conversion efficiency from AC power to DC power, with the AC power introduced into the vertical diode on the horizontal axis.
  • the resistance value is the set value of the variable resistor. From Fig. 8, it can be seen that the vertical diode obtained in Example 13 converts 1 GHz AC power with an efficiency of about 9%, which is more than one order of magnitude higher than the reported efficiency for solution-processed diodes.
  • Example 7 A vertical diode having a layer structure of a surface-modified Au bilayer electrode/P(NDI-2T)/Au electrode was fabricated in the same manner as in Example 6 , except that in (5) (RuMes*Cp) 2 was changed to CoCp 2. The current-voltage characteristics of the obtained vertical diode are shown in FIG.
  • Comparative Example 2 A vertical diode having a layer structure of an unmodified Au bilayer electrode/P(NDI-2T)/Au electrode was fabricated in the same manner as in Example 6, except that steps (4) to (8) were not performed. The current-voltage characteristics of the obtained vertical diode are shown in FIG.
  • Example 8 An ITO electrode whose surface was modified with a low molecular weight hydrophobic closed shell cation derived from (RuMes*Cp) 2 was prepared by the following procedure. The obtained surface-modified ITO electrode was subjected to photoelectron yield spectroscopy (PYS) measurement. The results are shown in FIG. 19 and Table 1.
  • the ITO electrode surface was cleaned by UV/ O3 treatment for 5 minutes.
  • (2) (RuMes*Cp) 2 was dropped onto a 2 mM butyl acetate solution of 2 on a UV/ O3 -treated ITO electrode, left to stand for 10 seconds, and then spin-coated at 3,000 rpm for 60 seconds.
  • (3) The coating was dried on a hot plate at 80° C. for 5 minutes.
  • Butyl acetate was dropped onto the ITO electrode, and the surface of the ITO electrode was washed by rotating at 3,000 rpm for 60 seconds.
  • the washed ITO electrode was dried on a hot plate at 80° C. for 5 minutes to obtain a surface-modified ITO electrode.
  • Comparative Example 4 An ITO electrode having a surface modified with PEI was prepared by the following procedure. The obtained surface-modified ITO electrode was subjected to photoelectron yield spectroscopy (PYS) measurement. The results are shown in FIG. 21 and Table 1.
  • the ITO electrode surface was cleaned by UV/ O3 treatment for 5 minutes.
  • a 0.2 wt % PEI aqueous solution prepared by dissolving PEI in pure water was dropped onto the ITO electrode, left to stand for 10 seconds, and then spin-coated at 3,000 rpm for 60 seconds.
  • the coating was dried on a hot plate at 90° C. for 30 minutes.
  • Butyl acetate was dropped onto the ITO electrode, and the surface of the ITO electrode was washed by rotating at 3,000 rpm for 60 seconds.
  • the washed ITO electrode was dried on a hot plate at 80° C. for 5 minutes to obtain a surface-modified ITO electrode.
  • XPS elemental analysis was performed on the surface-modified ITO electrode obtained in Example 8 and the unmodified ITO electrode obtained in Comparative Example 3. The results are shown in Fig. 22 and Table 2.
  • Fig. 22 shows that in the surface-modified ITO electrode obtained in Example 8, a layer of low-molecular-weight hydrophobic closed-shell cations derived from (RuCp*Mes) 2 is formed on the surface of the ITO electrode.
  • Example 8 The composition ratio of Ru determined by XPS measurement of the surface-modified ITO electrode obtained in Example 8 was 1/10 of that in the monolayer deposition model. This shows that in Example 8, the layer thickness of the low-molecular-weight hydrophobic closed-shell cation derived from (RuCp*Mes) 2 was less than a monolayer (1 nm or less). In Example 8, it is believed that the oxidation-reduction reaction causes electron injection and deposition of low-molecular-weight hydrophobic closed-shell cations, resulting in a shift in the electric field and vacuum level, which in turn reduces the work function of the surface-modified ITO electrode.
  • Example 9 A vertical diode having a layer structure of a surface-modified ITO electrode/P(NDI-2T)/Au electrode was fabricated by the following procedure.
  • the ITO electrode surface was cleaned by UV/ O3 treatment for 5 minutes.
  • a 2 mM butyl acetate solution of (RuMes*Cp) 2 was dropped onto the UV/ O3 -treated ITO, left to stand for 10 seconds, and then spin-coated at 3,000 rpm for 60 seconds.
  • the coating was dried on a hot plate at 80° C. for 5 minutes.
  • Butyl acetate was dropped onto the ITO electrode, and the surface of the ITO electrode was washed by rotating at 3,000 rpm for 60 seconds.
  • the washed ITO electrode was dried on a hot plate at 80° C. for 5 minutes to obtain a surface-modified ITO electrode.
  • a 1 wt % P(NDI-2T) solution prepared by dissolving P(NDI-2T) in o-dichlorobenzene was spin-coated at 2,000 rpm for 60 seconds.
  • the coating was dried on a hot plate at 80° C. for 20 minutes to form an organic semiconductor layer with a thickness of about 70 nm.
  • a 40 nm thick Au film was deposited on the organic semiconductor layer under high vacuum conditions using a vacuum resistance heating deposition machine, thereby obtaining a vertical diode.
  • Comparative Example 5 A vertical diode was fabricated by the following procedure.
  • the surface of the ITO electrode was cleaned by UV/ O3 treatment for 5 minutes to obtain an unmodified ITO electrode.
  • a 1 wt % P(NDI-2T) solution prepared by dissolving P(NDI-2T) in o-dichlorobenzene was spin-coated on the ITO electrode at 2,000 rpm for 60 seconds.
  • the coating film was dried on a hot plate at 80° C. for 20 minutes to form an organic semiconductor layer.
  • a 40 nm thick Au film was deposited on the organic semiconductor layer under high vacuum conditions using a vacuum resistance heating deposition machine, thereby obtaining a vertical diode.
  • Example 9 [Evaluation of coverage of low molecular weight hydrophobic ions] XPS elemental analysis was performed on the surface-modified ITO electrode obtained in Example 9 and the unmodified ITO electrode obtained in Comparative Example 5. The measurement results of Example 9 and Comparative Example 5 are shown in Figures 23 and 24, respectively.
  • Example 10 A vertical diode having a layer structure of a surface-modified ITO electrode/P(NDI-2T)/Au electrode was fabricated by the following procedure.
  • the ITO electrode surface was cleaned by UV/ O3 treatment for 5 minutes.
  • (2) (RuMes*Cp) 2 was dropped onto a 2 mM butyl acetate solution of 2 on a UV/ O3 -treated ITO electrode, left to stand for 10 seconds, and then spin-coated at 3,000 rpm for 60 seconds.
  • (3) The coating was dried on a hot plate at 80° C. for 5 minutes.
  • Butyl acetate was dropped onto the ITO electrode, and the surface of the ITO electrode was washed by rotating at 3,000 rpm for 60 seconds.
  • the washed ITO electrode was dried on a hot plate at 80° C. for 5 minutes to obtain a surface-modified ITO electrode.
  • Comparative Example 6 A vertical diode having a layer structure of an unmodified ITO electrode/P(NDI-2T)/Au electrode was fabricated in the same manner as in Example 10, except that steps (2) to (5) were not performed.
  • Example 11 A vertical diode having a layer structure of surface-modified Au electrode/PTAA (doped layer)/Au electrode was fabricated by the following procedure.
  • the Au electrode was treated with UV/ O3 .
  • the Au electrode was immersed in an aqueous solution containing hydroquinone HQ (1 mM) and 1,3-dimethylimidazolium hydroxide (0.1 mM) for 30 seconds and then dried by nitrogen blowing to obtain a surface-modified Au electrode.
  • PTAA was dissolved in o-dichlorobenzene to prepare a 2 wt % PTAA solution, which was then spin-coated onto the surface-modified Au electrode at 2,000 rpm for 60 seconds.
  • the coating film was dried on a hot plate at 80° C. for 20 minutes to form an organic semiconductor layer.
  • the organic semiconductor layer formed on the Au electrode was immersed in an aqueous solution containing sulfuric acid (1 mM), benzoquinone (10 mM), and lithium tetrakis(pentafluorophenyl)borate (10 mM) for 30 seconds, and then rinsed and washed with pure water.
  • Au electrodes were formed on the organic semiconductor layer by vacuum resistance heating deposition to obtain a vertical diode.
  • Example 12 A vertical diode having a layered structure of a surface-modified Au electrode/PTAA/Au electrode was fabricated in the same manner as in Example 11, except that (5) was not performed.
  • Example 11 The current-voltage characteristics of the vertical diode obtained in Example 11 and the vertical diode obtained in Example 12 are shown in FIG. 27 and FIG. 28, respectively. 27 and 28, it can be seen that in Example 11 in which a doped layer was formed in the vicinity of the Au electrode, the reverse current was suppressed and the rectification ratio was higher than that of Example 12.
  • the vertical diodes obtained in Examples 11 and 12 had a current density of about 100 Acm at a voltage of 3 V, and it can be seen that they exhibit a high current density even at a low voltage.
  • Example 13 A vertical diode having a layer structure of a surface-modified Au bilayer electrode/P(NDI-2T)/Au electrode was fabricated in the same manner as in Example 6, except that the P(NDI-2T) concentration in the P(NDI-2T) solution in (9) was changed to 0.5 wt %. The thickness of the P(NDI-2T) layer of this vertical diode was 25 nm. The current-voltage characteristics of the obtained vertical diode are shown in FIG.
  • the vertical diode obtained in Example 13 had a very thin organic semiconductor layer of 25 nm, but Figure 29 shows that it had excellent rectification characteristics and a high current density at low voltages.
  • Fig. 30 is a graph plotting the resistance value of the variable resistor when 70 mW or 42 mW of AC power is introduced into the vertical diode against the conversion efficiency from AC power to DC power on the horizontal axis. It can be seen from Fig. 30 that the vertical diode obtained in Example 13 converts 1 GHz AC power with an efficiency of about 8%, which is more than one order of magnitude higher than the reported efficiency of solution-processed diodes.
  • Example 14 A film of Au was formed on a glass substrate by resistance heating deposition, and an Au electrode was obtained by patterning using photolithography.
  • Au electrodes were immersed in an aqueous solution containing TPPA-OH (0.25 mM), fructose (1 M), and riboflavin (10 mM).
  • the Au electrode was washed with pure water to obtain a surface-modified Au electrode.
  • a solution containing N2200 (P(NDI-2T)) at a concentration of 0.8 wt % was spin-coated onto the surface-modified Au electrode at 2,000 rpm for 60 seconds.
  • the coating was baked at 80° C. for 20 minutes to form an organic semiconductor layer having a thickness of about 40 nm.
  • a Au top electrode (30 nm) was deposited on the organic semiconductor layer, and the Au top electrode was patterned using photolithography to obtain a vertical diode.

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Abstract

L'invention concerne une diode verticale dans laquelle une première électrode, une couche de semi-conducteur organique et une seconde électrode sont stratifiées de manière adjacente dans l'ordre indiqué, des ions hydrophobes de faible poids moléculaire étant fixés à la surface de la première électrode adjacente à la couche de semi-conducteur organique.
PCT/JP2024/031773 2023-09-04 2024-09-04 Diode verticale et procédé de fabrication de diode verticale Pending WO2025053187A1 (fr)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63237563A (ja) * 1987-03-26 1988-10-04 Mitsubishi Electric Corp 整流素子
JPH02260575A (ja) * 1989-03-31 1990-10-23 Mitsubishi Electric Corp 整流素子
JP2010087199A (ja) * 2008-09-30 2010-04-15 Dainippon Printing Co Ltd 有機半導体素子、および有機半導体素子の製造方法
JP2011216647A (ja) * 2010-03-31 2011-10-27 Dainippon Printing Co Ltd パターン形成体の製造方法、機能性素子の製造方法および半導体素子の製造方法
WO2012043025A1 (fr) * 2010-09-30 2012-04-05 リンテック株式会社 Composition adhésive conductrice, dispositif électronique, stratifié d'électrode positive, et procédé pour la fabrication du dispositif électronique

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63237563A (ja) * 1987-03-26 1988-10-04 Mitsubishi Electric Corp 整流素子
JPH02260575A (ja) * 1989-03-31 1990-10-23 Mitsubishi Electric Corp 整流素子
JP2010087199A (ja) * 2008-09-30 2010-04-15 Dainippon Printing Co Ltd 有機半導体素子、および有機半導体素子の製造方法
JP2011216647A (ja) * 2010-03-31 2011-10-27 Dainippon Printing Co Ltd パターン形成体の製造方法、機能性素子の製造方法および半導体素子の製造方法
WO2012043025A1 (fr) * 2010-09-30 2012-04-05 リンテック株式会社 Composition adhésive conductrice, dispositif électronique, stratifié d'électrode positive, et procédé pour la fabrication du dispositif électronique

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