WO2017069546A1 - Composition for work function reduction of metal oxide electron collection layer, inverted organic solar cell using same, and method for preparing inverted organic solar cell - Google Patents

Abstract

The present invention relates to a composition for work function reduction of a metal oxide electron collection layer, an inverted organic solar cell using same, and a method for preparing the inverted organic solar cell. According to the present invention, the surface of a metal oxide electron collection layer, which is a constituent element of an inverted organic solar cell, is modified by means of a neutral polymer and thus the work function of the metal oxide is reduced and a built-in potential is increased. And charge can be easily moved and collected by means of the forming of polymer nanodots due to the neutral polymer. Therefore, the efficiency of an inverted organic solar cell using a polymer can be greatly increased.

Description

Composition for reducing work function of metal oxide electron collecting layer, reverse structure organic solar cell using same, and method for manufacturing reverse structure organic solar cell

The present invention relates to a composition for reducing work function of a metal oxide electron collecting layer, an inverse structure organic solar cell using the same, and a method of manufacturing the inverse structure organic solar cell.

Recently, with the anticipation of the depletion of existing energy resources such as oil and coal, there is increasing interest in energy to replace them. Among them, solar cells have abundant energy resources and have no problems with environmental pollution.

Solar cells include solar cells that generate steam required to rotate turbines using solar heat, and solar cells that convert photons into electrical energy using the properties of semiconductors. Refers to an optical cell.

Most of the solar cells that are in practical use are inorganic solar cells using inorganic materials such as monocrystalline silicon, polycrystalline silicon, and amorphous silicon. However, since the inorganic solar cell is complicated to manufacture and is not suitable for general household use due to its high manufacturing cost, research on organic solar cells having a lower manufacturing cost through a relatively simple manufacturing process than the inorganic solar cell manufacturing process is performed. Is actively underway.

In addition, the organic solar cell can be made into a thin film with a thickness of several hundred nm and can be applied to a flexible structure, which is expected to be applied to various applications such as presenting the potential as an energy source of the future mobile information system. .

A general organic solar cell includes a lower electrode layer formed on a substrate, a hole transport layer formed in contact with the surface of the lower electrode layer, at least one active layer formed in contact with the surface of the hole transport layer, and an upper electrode layer formed on the active layer. do. When light is projected onto the organic solar cell, positive charges (holes) and negative charges (electrons) are generated in the active layer, electrons are moved to the electrode on the active layer, and holes are moved to the hole transport layer. The active layer of the conventional organic solar cell is an electron donor material poly (3-hexylthiophene) (hereinafter referred to as P3HT) and an electron acceptor material 1- (3-methoxycarbonyl) -propyl- It is prepared using a mixture of 1-phenyl- (6,6) C ₆₁ (1- (3-methoxycarbonyl) -propyl-1-phenyl- (6,6) C ₆₁ , hereinafter PCBM).

As the high efficiency, long life and simplification of the device structure of the organic solar cell are required, an organic solar cell having an inverse structure is stable in air while utilizing metal oxides such as TiO ₂ and ZnO to solve the problem. And, it is emerging as the most representative method that can be applied to the roll-to-roll process.

Inversely structured organic solar cells contain electrons from transparent electrodes (e.g., ITO or FTO) in contrast to the collection of holes from transparent electrodes such as indium-tin oxide (ITO) in the device structure of conventional positive structure organic solar cells. Collected to act as a cathode (cathode), the anode (Anode) may be used a metal such as Au, Ag.

The device structure of the reverse structure organic solar cell as described above may not use a metal such as Ca or Al, which is a highly reactive electron collecting electrode (cathode) used in a general positive structure organic solar cell device, and both a positive electrode and a negative electrode may be used. The high work-function allows the use of materials that are not reactive to air or moisture.

In addition, in the case of using a metal oxide other than an organic material as the electron collecting layer of the inverse structure organic solar cell, it has excellent transparency in the visible light region, excellent charge transport ability, and is stable in air. Attempts have been made to apply metal oxides formed by solution processes to reverse structure organic solar cell devices.

It is an object of the present invention to provide a composition for reducing the work function of a metal oxide electron collecting layer capable of forming a polymer nanopoint, an inverse structure organic solar cell using the same, and a method of manufacturing the inverse structure organic solar cell.

The 1st aspect of this invention provides the composition for reducing work function of the metal oxide electron collection layer containing the compound represented by following formula (1).

[Formula 1]

Where

R is C _1-6 alkyl, C _2-6 alkenyl, C _2-6 alkynyl or C _1-6 alkoxy,

n is an integer of 50-10000.

A second aspect of the present invention includes a first electrode, a metal oxide electron collecting layer, a work function reducing layer, a photoactive layer, a hole collecting layer and a second electrode sequentially stacked on a substrate, wherein the work function reducing layer is It provides an inverse structure organic solar cell characterized in that it comprises a compound represented by the formula (1).

[Formula 1]

Where

R is C _1-6 alkyl, C _2-6 alkenyl, C _2-6 alkynyl or C _1-6 alkoxy,

n is an integer of 50-10000.

A third aspect of the invention, the first step of depositing a first electrode on a substrate; Stacking a metal oxide electron collecting layer on the first electrode; A third step of forming a work function reduction layer by coating a work function reduction composition of the metal oxide electron collection layer including the compound represented by Formula 1 on the metal oxide electron collecting layer; Stacking a photoactive layer on the work function reduction layer; Stacking a hole collecting layer on the photoactive layer; And a sixth step of stacking a second electrode on the hole collecting layer.

[Formula 1]

Where

R is C _1-6 alkyl, C _2-6 alkenyl, C _2-6 alkynyl or C _1-6 alkoxy,

n is an integer of 50-10000.

Hereinafter, the present invention will be described in detail.

In the present invention, when the surface of the metal oxide electron collecting layer, which is a component of the reverse structure organic solar cell, is modified by using a neutral polymer represented by Formula 1 as a work function reducing material, the work function of the metal oxide electron collecting layer is lowered. By increasing the built-in potential and facilitating the movement and collection of charges through the formation of polymer nanopoints by the neutral polymer, the efficiency of the inverse organic solar cell using the polymer is greatly improved. It was. That is, according to the present invention, when the poly (2-oxazoline) -based neutral polymer corresponding to the compound represented by Formula 1 is applied to the metal oxide electron collecting layer, the work function of the metal oxide electron collecting layer is reduced to reduce the metal oxide electron collecting layer. And the energy level between the photoactive layer and the photoactive layer were found to facilitate the transfer / collection of charge. The present invention is based on this.

As described above, the present invention provides a composition for reducing the work function of a metal oxide electron collecting layer comprising a compound represented by the following Chemical Formula 1.

[Formula 1]

Where

R is C _1-6 alkyl, C _2-6 alkenyl, C _2-6 alkynyl or C _1-6 alkoxy,

n is an integer of 50-10000.

In the present invention, when n is outside the above range, the synthesis may not be easy and the solubility may be degraded.

In the present invention, n is more preferably an integer of 100 to 6000.

In the present invention, the compound represented by Formula 1 may have a weight average molecular weight of 10000 to 500000, for example, 50000 to 100000.

In one embodiment, the composition for reducing the work function of the metal oxide electron collecting layer according to the present invention may include a compound (PEOz) represented by the following formula (2).

[Formula 2]

Wherein n is an integer from 50 to 10000.

In the present invention, the metal oxide electron collecting layer may be used in an inverse structure organic solar cell, and in addition to this, the work function of the metal oxide electron collecting layer may be applied without limitation to an organic device.

In the present invention, the metal oxide of the metal oxide electron collecting layer to which the work function reduction composition according to the present invention is applicable is zinc oxide (ZnO), titanium oxide (TiO _x , where x is 1, 2 or 3), oxidation Indium (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc tin oxide (Zinc Tin Oxide), gallium oxide (Ga ₂ O ₃ ), aluminum oxide, copper oxide (Copper (II) Oxide), copper aluminum oxide ( Copper aluminum oxide, zinc rhodium oxide, indium-gallium zinc oxide (IGZO) or mixtures thereof may be used, but is not limited thereto.

In addition, the present invention includes a first electrode (cathode), a metal oxide electron collecting layer, a work function reduction layer, a photoactive layer, a hole collecting layer and a second electrode (anode) sequentially stacked on a substrate as shown in FIG. 1, It provides an inverse structure organic solar cell, characterized in that the work function reducing layer comprises a compound represented by the following formula (1).

[Formula 1]

Where

R is C _1-6 alkyl, C _2-6 alkenyl, C _2-6 alkynyl or C _1-6 alkoxy,

n is an integer of 50-10000.

Inverse structure organic solar cell according to the present invention,

Stacking a first electrode on a substrate;

Stacking a metal oxide electron collecting layer on the first electrode;

A third step of forming a work function reduction layer by coating a work function reduction composition of the metal oxide electron collection layer including the compound represented by Formula 1 on the metal oxide electron collecting layer;

Stacking a photoactive layer on the work function reduction layer;

Stacking a hole collecting layer on the photoactive layer; And

It may be prepared by a method comprising a sixth step of stacking a second electrode on the hole collecting layer.

[Formula 1]

Where

R is C _1-6 alkyl, C _2-6 alkenyl, C _2-6 alkynyl or C _1-6 alkoxy,

n is an integer of 50-10000.

In the present invention, by applying the compound represented by the formula (1) as a work function reducing layer to reduce the work function of the metal oxide electron collecting layer as shown in Figure 2 to control the energy structure of the overall reverse structure organic solar cell device, that is, It is possible to improve the performance of the inverse structure organic solar cell.

In the present invention, the substrate may be a light-transmitting inorganic substrate or an organic substrate, or may be a substrate in which they are stacked in the same or different types. For example, the substrate may be glass, quartz, polyethylene terephthalate (PET), polyethylene naphthelate (PEN), polyimide (PI), polycarbonate (PC), polystyrene ( polystylene (PS), polyoxyethlene (POM), acrylonitile styrene copolymer (AS resin), Triacetyl cellulose (TAC), or mixtures thereof.

The first electrode is preferably a light transmissive material such that light passing through the substrate reaches the photoactive layer, and may serve as a cathode that receives electrons generated in the photoactive layer and transfers the electrons to the external circuit. The first electrode may be indium tin oxide (ITO), fluorinated tin oxide (FTO), indium zinc oxide (IZO), or aluminum-doped zinc oxide (Al-doped Zinc Oxide). , AZO), zinc oxide (ZnO), indium zinc oxide (IZTO), or mixtures thereof.

The first electrode may be formed by applying a transparent electrode material to one surface of the substrate or coating in a film form using sputtering, E-Beam, thermal evaporation, spin coating, screen printing, inkjet printing, doctor blade or gravure printing. Can be.

The metal oxide electron collecting layer may also be referred to as a metal oxide electron extraction layer, and may serve to receive electrons generated in the photoactive layer and transfer them to the first electrode. As the metal oxide of the metal oxide electron collecting layer, various metal oxides mentioned in the work function reduction composition according to the present invention may be used without limitation.

In the present invention, in order to lower the work function of the metal oxide electron collecting layer, a work function reducing layer including the neutral polymer represented by Chemical Formula 1 is formed on the surface of the metal oxide electron collecting layer. The work function reduction layer may be formed in a nano-dot structure. As the work function reduction layer is formed in the nano-point structure, the area with the electrode can be increased, thereby collecting a larger amount of charge.

In the present invention, the work function reduction layer may be formed by coating a solution having a concentration of 1 to 10 mg / ml of the compound represented by Chemical Formula 1 on the metal oxide electron collecting layer. Preferably, it is preferable to use a solution having a concentration of 2 to 5 mg / ml of the compound represented by Formula 1 in terms of work function reduction efficiency. The work function reduction layer is deposited on the metal oxide electron collecting layer through a solution process, for example, spin coating or spray coating, to form a coating layer on the surface of the metal oxide electron collecting layer and lower its work function. In this case, the coating solution for forming the work function reduction layer may use an organic solvent such as methanol, chlorobenzene, chloroform or para xylene as a solvent.

A photoactive layer is formed on the work function reduction layer. The photoactive layer may be formed by applying a mixed solution of an electron acceptor material and an electron donor material onto the work function reduction layer and then drying the solvent. The coating process may use a known coating method such as spin coating, spray coating, doctor blade coating, and inkjet printing, and may be preferably performed by spin coating.

The electron donor material refers to a material that absorbs sunlight to form electron-hole pairs (excitons) and moves holes separated at the pn junction interface between the electron donor material and the electron acceptor material toward the anode. .

The electron donor material may be a conjugated polymer that can be used as a p-type semiconductor, polythiophene-based, polyfluorene-based, polyaniline-based, polycarbazole-based, polyvinylcarba It may be a sol (polyvinylcarbazole), polyphenylene (polyphenylene), polyphenylenevinylene (polyphenylenevinylene), polysilane (polysilane), polythiazole (polythiazole) or a copolymer thereof. For example, electron donor materials include PBDTTT-C-T, PTB7-Th, PBDTT-S-TT, PBDT-TS1, PBDTTT-C, and PTB7.

On the other hand, the electron acceptor material means a material that serves to move the electrons separated at the pn junction interface in the photoactive layer toward the cathode. For example, the electron acceptor material is fullerene and PC61BM ([6,6] -phenyl-C61-butyric acid methyl ester), PC ₇₁ BM ([6,6] -phenyl- which can be used as an n-type semiconductor. C ₇₁ -butyric acid methyl ester), PC81BM ([6,6] -phenyl-C81-butyric acid methyl ester), and fullerene derivatives such as ICBA (indene-C60 bisadduct).

The hole collecting layer is a p-type buffer layer that allows the holes generated in the photoactive layer to be easily transferred to the anode, also called a hole transport layer.

In the present invention, the hole collecting layer may be a conductive metal oxide, a compounded organic of poly (3,4-ethylenedioxythiophene) [PEDOT] and poly (3-styrenesulfonate) [PSS], or a mixture thereof. As the conductive metal oxide, at least one of WO ₃ , V ₂ O ₃ , MoO ₃ , and the like may be used.

The second electrode is a layer serving as an anode that finally collects holes and delivers the holes to an external circuit. The second electrode may be any one selected from metals, alloys, conductive polymers, other conductive compounds, and combinations thereof. However, the second electrode is preferably a material having a high oxidation stability against exposure to the atmosphere. For example, in the case of a metal, it is preferable to use a material having a high work function such as Cu, Ag, Au, W, Ni, and Ti. desirable.

Except for the work function reduction layer, each of the above layers may be formed by thermal image deposition, electron beam deposition, sputtering, ion plating or chemical vapor deposition, and the work function reduction layer may be formed by a solution process as described above. The electrodes may be formed by applying an electrode forming paste including a metal and then heat treatment.

The present invention lowers the work function of the metal oxide by modifying the surface of the metal oxide electron collecting layer, which is a component of the inverse structure organic solar cell, using a neutral polymer, thereby increasing the built-in potential, and the neutral polymer. By facilitating the movement / collection of charges through the formation of polymer nano-dots, the efficiency of the inverse organic solar cell using the polymer can be greatly improved. As a result, it is expected to accelerate the commercialization of polymer solar cells by developing high efficiency organic solar cells of 10% or more, and is expected to play a big role in the development of organic solar cells that can be bent and worn on the body.

1 is a schematic diagram of an inverse structure organic solar cell according to the present invention.

2 is a schematic diagram of an energy structure of an inverse organic solar cell according to the present invention.

Figure 3 shows the results of the UPS measurement on each surface according to the PEOz concentration control on the ZnO surface.

Figure 4 shows the results of the EFM measurement on each surface according to the PEOz concentration control on the ZnO surface.

FIG. 5 is a schematic diagram illustrating a lower work function of ZnO based on the results of UPS and EFM measurements.

6 is a schematic diagram showing a laminated structure of an inverse structure organic solar cell according to an embodiment of the present invention.

7 is a schematic diagram showing the energy structure of an inverse structure organic solar cell according to an embodiment of the present invention.

FIG. 8 is a current density-voltage graph of the device according to the concentration of PEOz for the organic solar cell of the inverse structure type fabricated in Example 2. FIG.

9 is a result of measuring the external quantum efficiency of the device according to the concentration of PEOz for the organic solar cell of the reverse structure type prepared in Example 2.

10 is a result of analyzing the performance of the various indicators of the reverse structure organic solar cell according to the concentration of PEOz for the reverse structure type organic solar cell prepared in Example 2.

FIG. 11 is an AES imaging result of a work function reduction layer, that is, a PEOz layer (ZnO / PEOz 4 mg / ml) and an untreated ZnO surface, by adjusting the concentration of PEOz to 4 mg / ml.

12 is a result of analyzing the surface morphology of the work function reduction layer, that is, the PEOz layer, by modifying the ZnO surface by adjusting the concentration of PEOz to 4 mg / ml.

FIG. 13 is a schematic view of an inverse structure organic solar cell according to the present invention including a PEOz layer having a nanopoint structure as a work function reduction layer.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention more specifically, but the scope of the present invention is not limited by these examples.

Example  One: PEOz  For metal oxide layers Work function Reduction  Research

Methanol is used as a solvent to modify the ZnO surface through concentration control (thickness control) (0, 1, 2, 4, 8 mg / ml) of PEOz (weight average molecular weight: 50000 Da, polydispersity index = 3.5) (ultraviolet photoelectron spectroscopy) was measured as follows. PEOz was obtained from Sigma-Aldrich (USA) and used without further purification.

The UPS was measured using an ultra-high vacuum (UHV) UPS system (ESCALAB 250Xi, Thermo Scientific) at 1 × 10 ⁻⁹ mbar using a He I (21.2 eV) UV light source. All samples were biased at -5 V and the energy scale of the UPS spectrum was corrected to the Fermi level of the thermally-evaporated-cleaned Ag substrate. The valence band energy of the ZnO layer was obtained at 7.7 eV from the low binding energy portion of the corresponding UPS spectrum after calibration with the cleaned Ag reference electrode, and the conduction band energy of the ZnO layer was from the valence band energy (3.4 eV) Calculated by subtracting The valence band maximum of the PEOz-coated ZnO layer was calculated using the following equation:

_{E VBM = P IN - (E} CF - E ON)

Where E _VBM , P _IN , E _CF and E _ON are valence band maximum, incident photon energy (21.2 eV), binding energy in the cutoff region, and onset binding energy, respectively.

As a result, as shown in Figure 3, it was confirmed that the binding energy moves.

In addition, ZnO surface was modified through the concentration control (thickness control) (0, 4, 8 mg / ml) of PEOz using methanol as a solvent, and the electrostatic force microscopy (EMF) was measured as follows.

The work function was measured with EFM (XE-150, Park Systems) and calibrated with highly ordered pyrolytic graphite (HOPG).

As a result, as shown in Figure 4, it can be seen that the work function (Work Function) of ZnO is lowered.

Based on the results of the UPS and EFM measurement, it is shown in Figure 5 that the work function of ZnO is lowered.

Example 2: Fabrication of Inverse Structure Organic Solar Cell Using PEOz

An organic solar cell of an inverse structure type having an energy structure as shown in FIG. 7 in a laminated structure as shown in FIG. 6 while using a PEOz-containing work function reduction coating solution was manufactured as follows.

PTB7-Th (weight average molecular weight = 126000 Da, polydispersity index = 2.5) and PC71BM (purity> 99%) were obtained from 1-material (1-Material, Canada) and Nano-C (Nano-C, United States), respectively. Purchased. PEOz (weight average molecular weight: 50000 Da, polydispersity index = 3.5) was obtained from Sigma-Aldrich (USA) and used without further purification. Using methanol as a solvent, a coating solution for reducing work function was prepared for each PEOz concentration (0, 1, 2, 4, 6, 8 mg / ml). The binary polymer: fullerene solution is present in the presence of 1,8-dioodooctane (DIO) (CB: DIO = 97: 3 parts by volume) at a solid concentration of 20 mg / ml (PTB7-Th: PC71BM = 1: 1.5 parts by weight). It was prepared using chlorobenzene (CB) as a solvent under vigorous stirring at room temperature for 12 hours prior to spin coating. ZnO precursor solution was dissolved zinc acetate dihydrate (Sigma-Aldrich, 1g) and ethanolamine (Sigma-Aldrich, 0.28 g) in 2-methoxyethanol (Sigma-Aldrich, 10 mL) and stirred at 60 ° C. for 3 hours. Then it was prepared by stirring at room temperature for 12 hours before spin coating.

Indium-tin oxide (ITO) -coated glass substrates (sheet resistance = 10 Ω / cm ² ) were patterned by photolithography / etching process. The pre-patterned ITO-glass substrate was cleaned with acetone and isopropyl alcohol in an ultrasonic cleaner and then dried under running nitrogen. The dried ITO-glass substrate was treated for 20 minutes inside the UV-ozone chamber to remove any residual organic residue on the substrate surface and make the ITO surface hydrophilic. The ZnO precursor solution was spin coated onto the cleaned ITO-glass substrate and the resulting ITO / ZnO sample was annealed at 200 ° C. for 1 hour in air. After cooling to room temperature, the PEOz solution was spin coated onto the surface of the ZnO layer and annealed at 120 ° C. for 15 minutes. PEOz-coated samples were placed in a nitrogen filled glove box for photoactive layer coating. The PTB7-Th: PC ₇₁ BM BHJ layer was spin coated on top of the PEOz-coated ZnO layer and dried for 20 minutes inside the glove box. These samples were then placed in a vacuum chamber in an argon filled glove box. In the vacuum chamber, MoO ₃ (10 nm) and Ag (80 nm) were sequentially deposited on top of the BHJ layer through a shadow mask at a vacuum of 2 × 10 ⁻⁶ Torr. The active area of the device was 0.05 cm ² or 0.09 cm ² .

Example 3 Performance Analysis of Inverse Structured Organic Solar Cells According to the Present Invention

For the inverse structure type organic solar cell fabricated in Example 2, the current density-voltage graph of the device according to the concentration of PEOz was calculated using a solar simulator (92250A-1000, Newport-Oriel) and an electrometer (Model 2400, Keithley's solar cell measurement system was used.

The results are shown in FIG.

8, it can be seen that the characteristics of the device having a concentration of PEOz of 4 mg / ml is the best.

In addition, the external quantum efficiency (EQE) according to the concentration of PEOz for the inverse structure type organic solar cell manufactured in Example 2 is a light source (Tungsten-Halogen lamp, 150 W, ASBN-W, Spectral Products) And a special EQE measurement system equipped with a monochromatic spectrometer (CM110, Spectral Products).

The results are shown in FIG.

9, it can be seen that the external quantum efficiency is higher when the concentration of PEOz is 4 mg / ml in most visible light regions.

In addition, the performance of the inverse structure organic solar cell according to the concentration of PEOz with respect to the organic structure of the inverse structure type organic solar cell prepared in Example 2 as described below in various indicators and the results are shown in Table 1 and FIG. Indicated.

The results of Table 1 and Figure 10, it can be seen that the performance of the device is the best when the concentration of PEOz is 4 mg / ㎖.

Example 4 Work Function Reduction Layer Surface Analysis According to the Present Invention

Using a chlorobenzene as a solvent, the concentration of PEOz was adjusted to 4 mg / ml, thereby modifying the ZnO surface on the glass substrate / ITO, that is, a PEOz layer (ZnO / PEOz 4 mg / ml) and untreated ZnO. Surfaces were measured by Auger Electron Spectroscopy (AES) imaging.

First, a glass substrate / ITO / ZnO layer was laminated under the same conditions as in Example 2, and the surface of the ZnO was modified at a concentration of 4 mg / ml of PEOz. Then, AES imaging was measured.

The results are shown in FIG.

11, it can be seen that the PEOz layer is formed in a nano-dot structure.

In addition, the surface morphology of the PEOz layer was measured by AFM (atomic force microscopy, Nanoscope IIIa, Digital Instruments).

The results are shown in FIG.

12 also shows that the PEOz layer is formed with a nano-dot structure.

Therefore, when the surface treatment of the PEOz layer on the ZnO surface through the above results, it can be seen that the device efficiency is greatly improved by the nano-point structure.

A schematic diagram of the inverse structure organic solar cell according to the present invention including the PEOz layer having the nanopoint structure as the work function reduction layer is illustrated in FIG. 13.

Claims (10)

A composition for reducing the work function of a metal oxide electron collecting layer comprising a compound represented by Formula 1 below: [Formula 1]

Where R is C _1-6 alkyl, C _2-6 alkenyl, C _2-6 alkynyl or C _1-6 alkoxy, n is an integer of 50-10000. The composition of claim 1, wherein the metal oxide electron collecting layer is used in an inverse structure organic solar cell. The method of claim 1, wherein the metal oxide of the metal oxide electron collecting layer is zinc oxide (ZnO), titanium oxide (TiO _x , where x is 1, 2 or 3), indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc tin oxide, gallium oxide (Ga ₂ O ₃ ), aluminum oxide, copper oxide (Copper (II) Oxide), copper aluminum oxide, zinc rhodium oxide (Zinc Rhodium Oxide), IGZO (indium-Gallium Zinc Oxide) or a mixture thereof. A first electrode, a metal oxide electron collecting layer, a work function reducing layer, a photoactive layer, a hole collecting layer and a second electrode sequentially stacked on a substrate, wherein the work function reducing layer comprises a compound represented by the following formula (1) Inverse structure organic solar cell characterized by: [Formula 1]

Where R is C _1-6 alkyl, C _2-6 alkenyl, C _2-6 alkynyl or C _1-6 alkoxy, n is an integer of 50-10000. The metal oxide of claim 4, wherein the metal oxide of the metal oxide electron collecting layer is zinc oxide (ZnO), titanium oxide (TiO _x , where x is 1, 2 or 3), indium oxide (In ₂ O ₃ ), or tin oxide. (SnO ₂ ), Zinc Tin Oxide, Gallium Oxide (Ga ₂ O ₃ ), Aluminum Oxide, Copper Oxide (Copper (II) Oxide), Copper Aluminum Oxide, Zinc Oxide Inverse structure organic solar cell, characterized in that Rhodium Oxide), IGZO (indium-Gallium Zinc Oxide) or a mixture thereof. The inverse structure organic solar cell of claim 4, wherein the work function reduction layer is formed in a nano-dot structure. The inverse structure organic solar cell of claim 4, wherein the work function reduction layer is formed by coating a solution having a concentration of 1 to 10 mg / ml represented by Chemical Formula 1 on a metal oxide electron collecting layer. . Stacking a first electrode on a substrate; Stacking a metal oxide electron collecting layer on the first electrode; A third step of forming a work function reduction layer by coating a work function reduction composition of the metal oxide electron collection layer including the compound represented by Formula 1 on the metal oxide electron collecting layer; Stacking a photoactive layer on the work function reduction layer; Stacking a hole collecting layer on the photoactive layer; And Method of manufacturing an inverse structure organic solar cell comprising a sixth step of depositing a second electrode on the hole collection layer: [Formula 1]

Where R is C _1-6 alkyl, C _2-6 alkenyl, C _2-6 alkynyl or C _1-6 alkoxy, n is an integer of 50-10000. The method of claim 8, wherein the composition for reducing work function used in the third step is a solution having a concentration of 1 to 10 mg / ml of the compound represented by the formula (1). The method of claim 8, wherein the coating of the work function reduction composition in the third step is carried out through a solution process.

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