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WO2009097360A1 - Bains d'électrodéposition à l'indium pour dépôt de couche mince - Google Patents

Bains d'électrodéposition à l'indium pour dépôt de couche mince Download PDF

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WO2009097360A1
WO2009097360A1 PCT/US2009/032291 US2009032291W WO2009097360A1 WO 2009097360 A1 WO2009097360 A1 WO 2009097360A1 US 2009032291 W US2009032291 W US 2009032291W WO 2009097360 A1 WO2009097360 A1 WO 2009097360A1
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acid
solution
citrate
plating
solvent
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Jiaxiong Wang
Serdar Aksu
Bulent Basol
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SoloPower Inc
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SoloPower Inc
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/54—Electroplating: Baths therefor from solutions of metals not provided for in groups C25D3/04 - C25D3/50
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F10/00—Individual photovoltaic cells, e.g. solar cells
    • H10F10/10—Individual photovoltaic cells, e.g. solar cells having potential barriers
    • H10F10/16—Photovoltaic cells having only PN heterojunction potential barriers
    • H10F10/167—Photovoltaic cells having only PN heterojunction potential barriers comprising Group I-III-VI materials, e.g. CdS/CuInSe2 [CIS] heterojunction photovoltaic cells
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00—Constructional details of devices covered by this subclass
    • H10F77/10—Semiconductor bodies
    • H10F77/12—Active materials
    • H10F77/126—Active materials comprising only Group I-III-VI chalcopyrite materials, e.g. CuInSe2, CuGaSe2 or CuInGaSe2 [CIGS]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/541—CuInSe2 material PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • This invention relates to indium (In) electroplating methods and chemistries to deposit uniform, defect free and smooth In thin films with high plating efficiency and repeatability. These In thin films may be used in fabrication of electronic and semiconductor devices such as thin film solar cells.
  • Indium (In) is an important metal used in semiconductor and electronics industries. Indium is generally recovered as a by-product from zinc and lead-zinc production. Electrodeposition is a common method to recover bulk In. A number of In electroplating baths have also been formulated to deposit layers of In on various conductive substrates. For example, In plating baths containing sulfamate (US Pat. 2458839), cyanide (US Pat. 2497988), alkali hydroxides (US Pat. 2287948), tartaric acid (US Pat. 2423624), and fluoborate (US Pat. 3812020, US Pat. 2409983) have been developed and commercialized.
  • In can also be plated from organic solvent based solutions such as formamide (US Pat. 2452361).
  • Some of the In alloys that can be electroplated include indium-silver (US Pat. 1935630), indium-tin (US Pat. 6331240) and indium-nickel (US Pat. 4626324, US Pat. 4686015).
  • indium-silver US Pat. 1935630
  • indium-tin US Pat. 6331240
  • indium-nickel US Pat. 4626324, US Pat. 4686015
  • it is possible to deposit In and In alloy layers using various prior-art plating chemistries such layers may not be suitable for preparation of smooth, uniform, defect-free In films with sub-micron thickness that are needed for thin film solar cell applications.
  • Common defects in electroplated In layers include holes, or pinholes as will be described later.
  • Cu(In 5 Ga)(Se 5 S) 2 or CIGS(S) films which are the most advanced compound absorbers for polycrystalline thin film solar cells.
  • a thin In layer for example, may be electroplated on a Cu layer.
  • the Cu/In precursor stack thus obtained may then be reacted with Se to form a CuInSe 2 or CIS absorber. Reaction with S would form a CIS(S) layer.
  • CIGS or CIGS(S) formation Ga is also included in the precursor stack.
  • the CIGS(S) absorber may be used in fabrication of thin film solar cells with a structure of "contact/CIGS(S)/buffer layer/TCO", where contact is a metallic layer such as a Mo layer, the buffer layer is a thin transparent film such as a CdS film and TCO is a transparent conductive oxide layer such as a ZnO and/or ITO layer.
  • contact is a metallic layer such as a Mo layer
  • the buffer layer is a thin transparent film such as a CdS film
  • TCO is a transparent conductive oxide layer such as a ZnO and/or ITO layer.
  • the cell efficiency is a strong function of the molar ratio of IB/IIIA. If there are more than one Group IIIA materials in the composition, the relative amounts or molar ratios of these IIIA elements also affect the properties.
  • the efficiency of the device is a function of the molar ratio of Cu/(In+Ga).
  • some of the important parameters of the cell such as its open circuit voltage, short circuit current and fill factor vary with the molar ratio of the IIIA elements, i.e. the Ga/(Ga+In) molar ratio.
  • Cu/(In+Ga) molar ratio is kept at or below 1.0.
  • a low resistance copper selenide phase may form, which may introduce electrical shorts within the solar cells.
  • the optical bandgap of the absorber layer increases and therefore the open circuit voltage of the solar cell increases while the short circuit current typically may decrease. It is important for a thin film deposition process to have the capability of controlling both the molar ratio of IB/IIIA, and the molar ratios of the Group IIIA components in the composition. Therefore, if electrodeposition is used to introduce the In into the film composition, it is essential that the electroplated In films have smooth morphology and be free of defects such as pinholes. It should be appreciated that any protrusions in the In film will cause an In-rich region in the CIGS(S) absorber obtained after reaction with Se and/or S.
  • any pinholes or regions with thinner In would yield Cu-rich or In-poor regions which, after reaction with Se and/or S would turn into copper selenide-rich regions with low resistance, which would introduce electrical shunt between the contact layer and TCO layer of the solar cell, reducing the conversion efficiency of the device.
  • Such non-uniform layers cannot be used for high efficiency solar cell manufacturing.
  • the In cyanide bath contains very toxic potassium cyanide and its cathode efficiency drops down with aging of the bath and thus In thickness changes with time.
  • the alkali hydroxide In plating baths may result in corrosion on the plated In surfaces and they usually need some additives to increase the stability and the deposition or plating efficiencies. Control of additives is difficult and costly in the manufacturing environment.
  • the In sulfamate plating solution generates In thin films with a cathode efficiency of about 90%.
  • this bath requires some additives to improve the quality and morphology of the deposited layers. Organic additives may gradually decompose and start affecting deposit quality in a negative manner.
  • gray In deposits can be attributed to the deposition of double salts.
  • the deposits may not be pure metallic In but may comprise In salts.
  • the low cathodic current efficiencies might be attributed to the dilute In 3+ concentration (0.02 M). It is possible that the authors kept this concentration low to avoid precipitation of In + species within the relatively high pH ranges they selected for formulations.
  • the present invention relates to an In electroplating bath to deposit silvery white, uniform, substantially defect-free, smooth and pure metallic In films with high cathodic current efficiency and repeatability. Such layers may be used in fabrication of electronic devices such as thin film solar cells.
  • the present invention provides a plating solution or bath for application of an In layer on a conductive surface.
  • the solution includes an In source, a weak acid and its conjugate pair salt, and a solvent, wherein the solution provides a sub-micron thick chemically pure In film on the conductor with a cathodic plating efficiency of about 95-100%, preferably an efficiency of 98-100%.
  • the pH value of such solution is below about 4.0.
  • the In plating bath of certain embodiments of the present invention features non- corrosive, environmentally green chemistry which is low cost and highly stable so that In layers with repeatable thickness and morphology may be electroplated employing simple maintenance of the bath in a manufacturing environment.
  • the In plating solution has been applied to roll-to-roll electroplating to obtain an In containing film possessing a sub-micron thickness on the surface of a conductor in a large scale manufacturing line.
  • Figure 1 is a schematic illustration of an In layer electroplated on a conductive bottom layer.
  • An embodiment of the invention provides an electroplating solution for application of a substantially pure indium (In) film onto a conductive surface at high plating efficiency, comprising a solvent, an In source providing In ions to the solvent with an In ion concentration of at least about 0.05 M, and a weak acid and a conjugate pair salt of the weak acid, wherein the pH value of the electroplating solution is below about 4.0.
  • the solvent may optionally comprise water, and is preferably aqueous.
  • the In source may be any suitable source of In ions and is preferably one or more of In-chloride, In-sulfate, In-acetate, In-carbonate, In- nitrate, In-perchlorate, In-phosphate, In-oxide and In-hydroxide.
  • Exemplary weak acids which are suitable for this embodiment are citric acid, acetic acid, formic acid, thioacetic acid, glycolic acid, lactic acid, ascorbic acid, malic acid, butanoic acid, and pentanoic acid.
  • the weak acid is citric acid.
  • the conjugate pair salt of the weak acid may be any suitable salt and in preferred embodiments is a sodium, lithium, potassium, ammonium or alkyl (e.g., Ci-C 6 alkyl) ammonium salts of the weak acid.
  • the conjugate pair salt is one or more of sodium citrate, lithium citrate, potassium citrate, and a salt of an organically modified citrate, wherein the organically modified citrate comprises a citrate moiety such that one or more organic groups replaces (a)one or more hydrogens that are directly connected to a carbon or oxygen bonded to carbon 2 of the citrate moiety, or (b) the hydroxyl group bonded to carbon 2 of the citrate moiety.
  • Another embodiment of the invention provides a method of obtaining a substantially pure and substantially defect- free In film on a surface of a conductor comprising the steps of (i) providing a solution with a pH value below 4 wherein that solution comprises a solvent, an In source providing In ions to the solvent with an In ion concentration of at least 0.05 M, a weak acid and a conjugate pair salt of such weak acid; (ii) applying the solution onto an anode and the surface of the conductor, (iii) establishing a potential difference between the anode and the conductor, and (iv) electrodepositing the substantially pure In film on the surface of the conductor.
  • the weak acid is citric acid and the conjugate pair salt is a citrate salt, preferably at least one of sodium citrate, lithium citrate, potassium citrate, and an organically modified citrate.
  • the In source includes one or more of In-chloride, In-sulfate, In-acetate, In-carbonate, In-nitrate, In-perchlorate, In-phosphate, In- oxide and In-hydroxide.
  • the temperature of the solution is within the range of 10-60° C during the step of electrodeposition and preferably is controlled within such range prior to the step of electrodeposition.
  • the present invention provides a method to electroplate In films onto conductive surfaces at close to 100% deposition efficiency and high repeatability.
  • the present invention may be used to manufacture Group IB/IIIA/VIA compound solar cell absorbers including Group IB (such as Cu), Group IIIA (such as Ga and In), and Group VIA (such as Se and S) elements.
  • Group IB such as Cu
  • Group IIIA such as Ga and In
  • Group VIA such as Se and S
  • a solar cell absorber layer To manufacture a solar cell absorber layer initially an absorber precursor layer must be formed over a base which may include a substrate and a contact layer formed on a surface of the substrate.
  • Figure 1 shows an absorber precursor structure 10 having a conductive bottom layer 12 and an In layer 14 electroplated on the conductive bottom layer 12 using the present invention.
  • the conductive bottom layer 12 is formed on the base 16 which may comprise the substrate and the contact layer (not shown).
  • the typical conductive bottom layers used in this invention may be copper (Cu) and gallium (Ga) layers.
  • another element e.g., selenium (Se), or Ga can be directly plated onto the resultant In layer to form multiple metal stacks.
  • the present invention may be used to manufacture Cu/In/Se, Cu/In/Ga/Se and other metallic stacks, which in turn may be employed in processing CIS or CIGS type solar cell absorbers.
  • the electrochemical methods have recently received more attention for CIGS film formation due to their potential low cost.
  • the CIGS films have been prepared with electrochemical co-deposition method from acidic solutions containing CuCl 2 , InCl 3 , GaCl 3 and SeO 2 (see for example, US Pat. 6872295).
  • the electrochemical co-deposition of CIS films was also performed from a solution containing Cu 2+ , In 3+ , Se 4+ and citrate salts, as reported in the literature (Oliveira et al., Thin Solid Films, vol:405, p: 129-134, 2000).
  • controlled amounts of Cu, In, Ga and sometimes Se are electrodeposited in the form of Cu, In, Ga and Se containing thin film precursor stacks such as Cu/In/Ga/Se, Cu/Ga/In/Se, In/Cu/Ga/Se, Ga/Cu/In/Se, In/Ga/Cu/Ga/Se, In/Ga/Cu/In/Se, Ga/In/Cu/Ga/Se, Ga/In/Cu/In/Se, Cu/Ga/Cu/In/Se, Cu/In/Cu/Ga/Se etc., on a base such as a substrate coated with a conductive contact layer.
  • thin film precursor stacks such as Cu/In/Ga/Se, Cu/Ga/In/Se, In/Cu/Ga/Se, Ga/Cu/In/Se, In/Ga/Cu/In/Se, Cu/In/Cu/Ga/Se etc.
  • These stacks may then be annealed, or reacted, optionally with more Se, sulfur (S) or sodium (Na), to form a uniform thin film of the CIGS(S) alloy or compound on the contact layer.
  • Se, sulfur (S) or sodium (Na) Se, sulfur (S) or sodium (Na)
  • the process yield in terms of compositional control may be improved compared to the above mentioned alloy plating approaches where two or more of the Cu, In, Ga, Se species are co-plated on the substrate.
  • the control of the thickness and morphology of the electrodeposited layers is extremely important.
  • High yield and repeatability of a solar cell manufacturing process utilizing two-stage processing and electrodeposition of at least one of a Cu layer, an In layer and a Ga layer critically depend on the repeatability of the deposited thickness of the electroplated layers, from run to run.
  • micro-scale compositional uniformity requires these electroplated films with sub-micron thickness to have smooth morphology with a surface roughness of typically less than 10% of the film thickness, and with desirable and controllable microstructure, which is typically a small-grain microstructure with sub-micron size grains.
  • Stacks utilizing In films with rough surface morphology would result in the In content to be changing locally, in micro-scale throughout the film although on the average the In content may be in the acceptable range.
  • the typical acceptable CIGS(S) film composition has a Cu/(In+Ga) molar ratio in the 0.8-1.0 range whereas the Ga/(In+Ga) molar ratio may be in the range of 0.3-0.5.
  • copper layers or Ga layers
  • the substrate may be a metallic foil, glass or polymeric sheet or web.
  • the Ru containing layer on the substrate surface may be a Ru layer, a Ru alloy layer, a Ru compound layer or a stack containing Ru such as a Mo/Ru stack or in general a M/Ru stack, where M is a conductor or semiconductor.
  • Indium electroplating on the Cu surface (or the Ga surface) can be carried out at various current densities, such as at 5, 10, 20 and 30 mA/cm 2 , using the electrolytes of the present invention. Both DC and/or variable (such as pulse or ramped) voltage/current waveforms may be used for electroplating the In layers.
  • this invention provides an efficient In plating bath employing weak acids and conjugates salts such as citrates. Films obtained using this solution are substantially free from defects such as pinholes since hydrogen bubble formation on the cathode during plating is drastically reduced by the high plating efficiency. Electronic applications such as solar cells may tolerate a total pinhole area to be about 0.0001% of the total film area. Therefore, substantially pinhole-free means that on a 1 cm 2 size In-plated surface the total are of the pinholes (number of pinholes times the average size of pinholes) is less than about 10 "6 cm 2 .
  • citrates have been used in the In electrodeposition before, as described above, it did not provide pure and uniform layers.
  • the optimized pH for the bath of the present invention is less than about 4, preferably less than about 3.5, more preferably less than 2.5, and most preferably the pH is about 2.
  • the citric acid H 3 Ch
  • the other 10% of the citrates may stay in the solution in the form of H 2 QfNa + that may, in turn, complex the In 3+ species in the form of [(H 2 Qf ) n In 3+ ] m+/" , where n may be in the range of 1-6 and m may be in the range of 0 -3.
  • n may be in the range of 1-6
  • m may be in the range of 0 -3.
  • most of In + cations in the solution of the present invention are not complexed with the citrates. This is an important difference of the present invention from the literature (see, e.g. Fouda et al.). In Fouda a pH value of 5 was utilized. In the solution of the present invention In precipitates as In(OH) 3 at such pH values.
  • the solubility product Of In(OH) 3 is IxIO "33 .
  • the citrate seems to be a weak complexing agent for In. Therefore, the main role the citrates play in the solution of this embodiment of the present invention may not be complexing. Instead, there may be two aspects operating in our bath. On one hand, the sodium citrate may form a kind of buffer solution with the citric acid to stabilize the solution pH value. On the other hand, citrate may consume some excess protons to reduce hydrogen generation during the In plating process.
  • a pH value of 5 was utilized in the work described by Fouda et al.
  • Use of low pH values in the present invention provides several benefits including: i) adjustment of pH to low values can be achieved using citric acid instead of other acids.
  • Citric acid is the acid of the citrate anions, which provide preferable plating results as explained before, ii)
  • Using citric acid allows control of the cation concentration in the bath. If, for example, Na- citrate was used solely as a source of citrate, the Na concentration and citrate concentration in the bath would be tied together.
  • citric acid in addition to its conjugated salt such as Na- citrate, we have independent means of controlling pH as well as the citrate concentration and Na concentration in the plating bath. This flexibility allows adjustment of the bath so that plating efficiencies close to 100% can be achieved for the first time.
  • the invention will now be further described with reference to certain examples, however the invention is not limited to the examples set forth herein.
  • the electroplating experiments in these examples were carried out using a potentiostat/galvanostat (EG&G Model 263 A). The solutions were stirred during plating. De-oxygenation was not found to be necessary during the In plating process although this may be helpful in reducing the In anode oxidation during plating.
  • the substrates for the plating tests included stainless steel and soda- lime glass, both coated with a contact layer comprising a Cu film on its surface. Indium was electroplated on the Cu surface and the results were evaluated. The surface areas for the substrates were varied from several cm 2 to several hundreds of cm 2 to understand the suitability of the method for large scale manufacturing.
  • Example 1 In plating bath containing citrates:
  • a set of exemplary aqueous plating solutions were prepared containing 0.1 - 0.3
  • InCl 3 0.2 - 0.5 M sodium citrate (Na 3 C 6 H 5 O 7 ), and 0.1 - 0.3 M citric acid (H 3 C 6 H 5 O 7 ).
  • the pH was adjusted to a range between 1.5 and 3.5.
  • Indium was electrodeposited on the Cu surfaces at current densities of 5-30 mA/cm . Highly adherent In films with surface roughness less than 10 nm were obtained for a thickness of 200-400 nm. The plating efficiency was measured and found to be in the 95 - 100% range.
  • the typical anode used in the plating was an In plate.
  • the resultant In films were shiny, silvery white, smooth and substantially defect free, as examined with SEM and optical microscopes. No hydrogen evolution could be observed during plating.
  • Indium was also plated on other metal surfaces using the citrate In plating baths with high plating efficiency.
  • An accelerated test that continuously lasted 80 hours demonstrated that the bath chemistry was stable without any oxide or hydroxide precipitation and the deposition efficiencies were repeatable.
  • Another plating bath containing 50 liters of the In plating solution was used to plate In onto the 6" x 8" substrates for nine months with repeatable results if the pH was adjusted about once in two weeks.
  • the In 3+ concentration was stable if the In plate was used for the anode and did not require any adjustment.
  • the In thickness was very repeatable and the non-uniformity over the whole 6" x 8" substrates could be controlled at levels below 2% of relative standard deviation for different locations on the substrate.
  • the web substrate used in this roll-to-roll plating line was 13" wide and moved at a speed of about 2 ft/min.
  • the current density used in the plating was about 10 mA/cm 2 . This plating process produced uniform, smooth and defect free In films demonstrating the suitability of the solution to large scale manufacturing.
  • Example 2 In plating bath containing glycine as the complexing agent:
  • An aqueous plating bath was formulated with 0.2 M InCl 3 and 0.5 M Glycine to compare the bath of the present invention with a bath comprising a complexing agent.
  • the pH was adjusted to the range of 2.0 - 2.5 using HCl.
  • the plating tests were carried out on Cu surfaces at current densities of 10 - 30 mA/cm 2 . All the In films looked shiny and smooth but the cathodic plating efficiencies were only about 60-85%. Extensive hydrogen bubbling was observed on the cathode surface during the plating, which resulted in defects and pinholes on the In films that were visible to naked eye.
  • Example 1 above demonstrated the good performance of citric acid and its conjugate pair citrate in the In plating bath. It should be appreciated that other acids and their conjugate pairs may play the same roles in other In plating baths with a pH less than about 4.0, preferably less than about 3.5.
  • acids include but are not limited to acetic acid, tartaric acid, phosphoric acid, oxalic acid, carbonic acid, ascorbic acid, boric acid, butanoic acid, thioacetic acid, glycolic acid, malic acid, formic acid, heptanoic acid, hexanoic acid, hydrocyanic acid, hydrofluoric acid, lactic acid, nitrous acid, octanoic acid, pentanoic acid, uric acid, sulfurous acid, sulfuric acid HSO 4 " , nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, octadecanoic acid, eicosanoic acid, tetracosanoic acid, etc.
  • All of these acids may be combined with Li + , Na + , K + , NH 4 + or (C n Hp n+ i ) ) 4 N + (e.g., where n may be 1 to 6) salts of their conjugate pairs and In + salts to form In plating baths with high efficiency.
  • water is the preferred solvent in the formulation of the In plating baths of the present invention, it should be appreciated that organic solvents may also be added in the formulation, partially or wholly replacing the water.
  • organic solvents include but are not limited to alcohols, acetonitrile, propylene carbonate, formamide, dimethyl sulfoxide, glycerin etc.
  • the DC voltage/current was utilized during the In electrodeposition processes in the present invention, it should be noted that pulsed or other variable voltage/current sources may also be used to obtain high plating efficiencies and high quality In deposits employing the In plating baths of the present invention.
  • the temperature of the In electroplating baths may be in the range of 5 - 120 0 C depending upon the nature of the solvent. It is preferable to keep this temperature below the boiling point of the solvent.
  • the preferred bath temperature for water based formulation is in the range of 10 - 60 0 C. The most preferred range is 15 - 30 0 C.
  • the electroplating baths of the present invention may comprise additional ingredients.
  • organic additives such as surfactants, suppressors, levelers, accelerators etc. may be included in the formulation to refine its grain structure and surface roughness.
  • Organic additives include but are not limited to polyalkylene glycol type polymers, propane sulfonic acids, coumarin, saccharin, furfural, acryonitrile, magenta dye, glue, SPS, starch, dextrose, etc. In fact, dextrose and triethanolamine were used in the In citrate baths of the present invention, but the difference is insignificant because the plated In films have already shown good qualities without any additives.
  • the present invention is directed to the electrodeposition of substantially pure In layers (more than about 99.5% In, preferably more than 99.9% In) since the electronics application and specifically CIGS(S) solar cell application of such layers require good thickness and compositional control.
  • trace amounts of other materials may be included in the bath formulation of the present invention without changing its fundamentals. For example, small amounts (typically less than 0.01M) Ga, Cu, S and/or Se may be present in the formulation, provided that they do not interfere with the high plating efficiency.
  • the In layers produced using the bath compositions of the present invention were successfully employed to fabricate some all-electroplated metallic stacks on bases comprising stainless steel substrates coated with contact layers comprising Mo and/or Ru.
  • stacks had various deposition sequences yielding base/Cu/Ga/In/Se, base/Cu/Ga/Cu/In/Se, base/Cu/In/Cu/Ga/Se, base/Cu/In/Ga/Se, base/Cu/Ga/Cu/In/Ga/Se and base/Ga/Cu/In/Se multiple layers.
  • a Ga citrate based electroplating bath developed by the present inventors (US Pat Appl Pub. 20070272558) was utilized for Ga depositions. The stacks were then reacted in a tube furnace at 500 0 C for 50 minutes under inlet gas to form Cu(In 5 Ga)Se 2 absorbers.
  • the Cu/(In+Ga) molar ratio was kept in the 0.8-0.9 range while the Ga/(In+Ga) molar ratio was nominally 50% in these samples.
  • a 100 nm thick CdS layer was chemically deposited onto the absorber surfaces yielding a base/Cu(In,Ga)Se 2 /CdS structure.
  • a ZnO containing transparent oxide layer was then deposited over the CdS films by the sputtering technique.
  • Solar cell was completed by printing Ni or Ag finger contacts over the transparent oxide layer. Solar cell efficiencies over 15% were recorded from these devices demonstrating the quality of the electrodeposited stacks comprising the In layers of the present invention. This efficiency value is the highest that has been achieved by a two stage process employing In electrodeposition for the precursor preparation.

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Abstract

La présente invention concerne des solutions d'électrodéposition à l'indium (In) qui sont utilisées pour déposer des films d'In uniformes, lisses, essentiellement exempts de défauts, et ayant une composition pure, avec près de 100 % d'efficacité de placage et de répétitivité. Dans un mode de réalisation, la solution de placage comprend une source d'In, de l'acide citrique et son sel de base conjuguée et un solvant. A une valeur de pH inférieure à 4,0, des couches d'In d'une épaisseur inférieure au micron et ayant une pureté proche de 100 % et une efficacité de placage proche de 100 % sont produites. De telles couches d'In sont utilisées dans la fabrication de dispositifs électroniques tels que des cellules solaires à film mince.
PCT/US2009/032291 2008-01-29 2009-01-28 Bains d'électrodéposition à l'indium pour dépôt de couche mince Ceased WO2009097360A1 (fr)

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TW200938662A (en) 2009-09-16
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EP2245216A1 (fr) 2010-11-03

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