WO2011033445A1 - PROCESS FOR THE PRODUCTION OF Cu(In,Ga)Se2/CdS THIN-FILM SOLAR CELLS - Google Patents
PROCESS FOR THE PRODUCTION OF Cu(In,Ga)Se2/CdS THIN-FILM SOLAR CELLS Download PDFInfo
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- WO2011033445A1 WO2011033445A1 PCT/IB2010/054126 IB2010054126W WO2011033445A1 WO 2011033445 A1 WO2011033445 A1 WO 2011033445A1 IB 2010054126 W IB2010054126 W IB 2010054126W WO 2011033445 A1 WO2011033445 A1 WO 2011033445A1
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- 238000000034 method Methods 0.000 title claims abstract description 39
- 239000010409 thin film Substances 0.000 title claims abstract description 15
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 8
- 229910017612 Cu(In,Ga)Se2 Inorganic materials 0.000 title 1
- 238000004544 sputter deposition Methods 0.000 claims abstract description 23
- 239000010408 film Substances 0.000 claims abstract description 20
- 239000000758 substrate Substances 0.000 claims abstract description 15
- 238000000151 deposition Methods 0.000 claims abstract description 12
- 239000006096 absorbing agent Substances 0.000 claims abstract description 11
- 229910000807 Ga alloy Inorganic materials 0.000 claims abstract description 10
- 230000008021 deposition Effects 0.000 claims abstract description 9
- 238000002360 preparation method Methods 0.000 claims abstract description 6
- 239000010949 copper Substances 0.000 claims description 31
- 229910052738 indium Inorganic materials 0.000 claims description 8
- 229910052733 gallium Inorganic materials 0.000 claims description 7
- 229910052711 selenium Inorganic materials 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 6
- 239000005361 soda-lime glass Substances 0.000 claims description 5
- 238000002844 melting Methods 0.000 claims description 4
- 230000008018 melting Effects 0.000 claims description 4
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 claims description 3
- 238000000137 annealing Methods 0.000 claims description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 2
- 239000011248 coating agent Substances 0.000 claims description 2
- 238000000576 coating method Methods 0.000 claims description 2
- 238000001552 radio frequency sputter deposition Methods 0.000 claims 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims 1
- 229910052760 oxygen Inorganic materials 0.000 claims 1
- 239000001301 oxygen Substances 0.000 claims 1
- 238000007711 solidification Methods 0.000 claims 1
- 239000000463 material Substances 0.000 description 10
- 238000001704 evaporation Methods 0.000 description 5
- 230000008020 evaporation Effects 0.000 description 5
- SPVXKVOXSXTJOY-UHFFFAOYSA-N selane Chemical compound [SeH2] SPVXKVOXSXTJOY-UHFFFAOYSA-N 0.000 description 4
- 229910000058 selane Inorganic materials 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 238000009776 industrial production Methods 0.000 description 2
- 239000011261 inert gas Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000002243 precursor Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 229910052717 sulfur Inorganic materials 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 239000005749 Copper compound Substances 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000010549 co-Evaporation Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 150000001880 copper compounds Chemical class 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000007731 hot pressing Methods 0.000 description 1
- AKUCEXGLFUSJCD-UHFFFAOYSA-N indium(3+);selenium(2-) Chemical compound [Se-2].[Se-2].[Se-2].[In+3].[In+3] AKUCEXGLFUSJCD-UHFFFAOYSA-N 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910001635 magnesium fluoride Inorganic materials 0.000 description 1
- 229910021424 microcrystalline silicon Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 230000007096 poisonous effect Effects 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 238000005546 reactive sputtering Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 238000007669 thermal treatment Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
- H01L31/1828—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
- H01L31/1832—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe comprising ternary compounds, e.g. Hg Cd Te
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
- H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
- H01L31/0264—Inorganic materials
- H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
- H01L31/0322—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312 comprising only AIBIIICVI chalcopyrite compounds, e.g. Cu In Se2, Cu Ga Se2, Cu In Ga Se2
-
- 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
- the present invention generally relates to the field of production of solar cells, in particular of the thin-film solar cells. More precisely, the invention relates to a process for the production of thin-film solar cells in which the absorber layer is constituted by Cu(ln,Ga)Se 2 , as well as a process for the preparation of such absorber layer.
- CdS thin-film solar cells in which the absorber layer is constituted by Cu(ln,Ga)Se 2 are already known.
- the structure of these solar cells comprises a soda- lime glass substrate, on which an Mo back contact is deposited by sputtering, a Cu(ln,Ga)Se 2 layer coevaporated in three stages, a CdS layer deposited by chemical bath, a sputtering-deposited double layer of resistive/conductive ZnO, Ni/AI grids obtained through e-beam evaporation, an antireflection MgF 2 coating and a photolithographic insulation.
- the Culn x Gai -x Se 2 /CdS solar cell with x is a soda- lime glass substrate, on which an Mo back contact is deposited by sputtering, a Cu(ln,Ga)Se 2 layer coevaporated in three stages, a CdS layer deposited by chemical bath, a sputtering-deposited double layer of resistive/
- 0.75 is the thin film device that has revealed, at laboratory level, the highest efficiency
- the main difficulty of bringing this three-stage process to industrial level lies in the fact that, by using large surface substrates, as required in an industrial process, the use of crossed-beams leads to the possibility of a composition of the material variable from zone to zone.
- the non-uniformity of the composition of the material represents, as known, a serious drawback given that it negatively affects the efficiency of the device, not allowing attaining high efficiency.
- Cu(ln,Ga)Se 2 is a quaternary material, in the areas where there is an excess of Cu, the Cu 2 Se binary phase can easily form and this, being unstable, frees Cu which causes short circuiting of the device.
- the alternative process is currently used in various research laboratories and in some industrial laboratories, such as Showa Shell in Japan, Sulfur Cell in Germany and Shell Solar in the United States, and consists in depositing, through sputtering or evaporation, overlapped layers of In, Cu and Ga or an In+Ga alloy on an Mo coated substrate. These layers are first mixed through high temperature annealing and then are subjected to a selenization process in an environment containing Se or H 2 Se.
- the aforedescribed process has the drawback of providing for the use of H 2 Se which is an extremely poisonous gas and which thus requires adopting extremely strict precautions when this gas is used especially at industrial production level.
- CulnSe 2 Another known process for the preparation of Cu(ln,Ga)(S,Se 2 ) absorber layers, described in S. Zweigart et al., Proceedings of the First World Conference on Photovoltaic Energy Conversion, (1994), pp 60-67, provides for - as regards the preparation of CulnSe 2 - the sequential deposition of InSe and Cu by evaporation followed by selenisation of the double layer of InSe-Cu starting from a room temperature up to a temperature exceeding 500°C.
- CulnGaSe 2 is obtained by depositing a mixed compound (ln,Ga)(Se,S) on Mo and then the material is selenized or sulphurized during the deposition of Cu.
- the final result is not entirely satisfactory in that the CulnSe 2 or CulnGaSe 2 film which is obtained reveals stoichiometric non-uniformity from one zone to another, i.e. the resulting film is not homogeneous.
- the aim of the present invention is to provide a method for the preparation of Cu(ln,Ga)Se 2 thin films to be used as absorbers in the industrial processes of producing thin-film solar cells of the Cu(ln,Ga)Se 2 /CdS type.
- the process of preparing a Cu(ln,Ga)Se 2 thin film according to the present invention provides for the deposition of a Cu-Ga alloy through continuous sputtering on a layer of CulnSe 2 and subsequent selenization.
- copper may vary from 30 to 70 % atomic and correspondingly gallium from 70 to 30 % atomic, preferably in the process according to the present invention a 50-50 (%) Cu-Ga alloy is used.
- the CulnSe 2 layer is prepared by successive sputtering deposition on a soda- lime glass layer, coated by a layer of Mo, a layer of ln 2 Se 3 and a layer of Cu, and then progressively heated up to 400-450°C for about 20-30 minutes leaving the materials of the layers to interact with each other for a sufficient period of time (other 20-30 minutes) to form a homogeneous CulnSe 2 precursor.
- the thermal treatment is followed by a step of selenisation under vacuum, at a temperature of 520-550°C and for 5-30 minutes, to complete the amount of Se in the CulnSe 2 film.
- the ln 2 Se 3 target is obtained in polycrystalline form by heating elementary In and Se, in 2 to 6 mm pieces, until the temperature exceeds the melting temperature of ln 2 Se 3 in inert gas atmosphere at low pressure.
- the use of a ln 2 Se 3 target prepared so as to be in polycrystalline form is deemed very important, in that, if a target obtained through "hot pressing" starting from ln 2 Se 3 powders were used, due to the high vapour tension of Se, discharge instability might occur and, if the cooling is not carried in a very efficient manner, cracks might be formed in the target.
- the Mo and Cu targets as well as the Cu-Ga alloy are instead available in the market, in particular at Testbourne Ltd. (UK).
- a soda-lime glass with an area measuring 1 inch 2 (6.45 cm 2 ) and 4 mm thickness is used as substrate.
- the substrate is mounted in a sputtering chamber where there are four targets, i.e. Mo, ln 2 Se 3 , Cu and a Cu-Ga alloy containing 50% atomic of Cu and 50% atomic of Ga.
- the ln 2 Se 3 target was prepared starting from elementary In and Se placed in special graphite or quartz containers and brought to a temperature exceeding the melting temperature of ln 2 Se 3 (890°C). Inert gas, in particular nitrogen, is introduced into the melting furnace at a pressure exceeding 10 atm to avoid the evaporation of the In and Se elements.
- the target which is thus formed is polycrystalline and it has the same density as the ln 2 Se 3 material.
- Deposited in sequence on the substrate in the sputtering chamber are: 1 ⁇ of
- Mo, 1.5 ⁇ of ln 2 Se 3 and 0.16-0.18 ⁇ of Cu are deposited through continuous sputtering, while ln 2 Se 3 is deposited through radio-frequency sputtering.
- the three overlapped Mo-ln 2 Se 3 -Cu layers are brought to the temperature of 450°C in about 30 minutes and left to interact with each other for other 30 minutes in a vacuum chamber. This allows forming a CulnSe 2 film which however reveals Se deficiency.
- the material is exposed to Se vapour for about 20 minutes, while it is kept at a temperature of 520°C.
- Selenization is performed in a specially designed vacuum chamber where the substrate is arranged above a crucible containing Se at a distance of a few centimetres.
- the selenized CulnSe 2 layer is coated by 800 A of Cu-Ga alloy deposited through continuous sputtering and it is selenized again through the procedure described above.
- the CulnGaSe 2 layer thus formed has a Ga content which varies through its thickness, i.e. more Ga is contained at the layer surface than within the layer. This allows the prohibited gap of the material to be larger at the surface than in the material itself and thus the open circuit potential that can be obtained in the solar cell is higher in the case where Ga is distributed uniformly over the whole material thickness.
- 600 A of CdS are deposited on the CulnGaSe 2 layer thus formed through radiofrequency sputtering followed by 800 A of pure ZnO and about 1 ⁇ of ZnO doped with 2% atomic of Al.
- Pure ZnO is deposited through continuous sputtering from a Zn target in presence of 0 2 (reactive sputtering), while ZnO(AI) is deposited through continuous sputtering from a ceramic target.
- a grid contact is formed over the ZnO(AI) layer through continuous spluttering.
Abstract
A process for the preparation of a CuInGaSe2 thin film useable as an absorber layer in CulnGaSe2/CdS solar cells, in which said thin film is obtained by sputtering deposition of a Cu-Ga alloy on a CuInSe2 film, deposited on a substrate covered by an Mo film, and subsequent selenization. Before selenization, In2Se3 and Cu are mixed in a vacuum chamber in the absence of Se. The process uses a polycrystalline target for the deposition of In2Se3. This process is suitable for the production - at industrial level - of CdS thin film solar cells in which the absorber layer is constituted by Cu(In1Ga)Se2.
Description
TITLE
PROCESS FOR THE PRODUCTION OF Cu(ln,Ga)Se2/CdS THIN-FILM SOLAR
CELLS
DESCRIPTION
Field of the Invention
The present invention generally relates to the field of production of solar cells, in particular of the thin-film solar cells. More precisely, the invention relates to a process for the production of thin-film solar cells in which the absorber layer is constituted by Cu(ln,Ga)Se2, as well as a process for the preparation of such absorber layer.
Background Art
CdS thin-film solar cells in which the absorber layer is constituted by Cu(ln,Ga)Se2 are already known. The structure of these solar cells comprises a soda- lime glass substrate, on which an Mo back contact is deposited by sputtering, a Cu(ln,Ga)Se2 layer coevaporated in three stages, a CdS layer deposited by chemical bath, a sputtering-deposited double layer of resistive/conductive ZnO, Ni/AI grids obtained through e-beam evaporation, an antireflection MgF2 coating and a photolithographic insulation. In particular, the CulnxGai-xSe2/CdS solar cell with x =
0.75 is the thin film device that has revealed, at laboratory level, the highest efficiency,
1. e. about 20% (I. Repins et al., Prog. Photovolt: Res. Appl. 2008; 16:235-239). This efficiency value is comparable to that of the best microcrystalline Si solar cells.
However, this efficiency was obtained by preparing the Cu(ln,Ga)Se2 absorber layer through a process which is efficient only at laboratory level, but which is difficult to apply at industrial level. As a matter of fact, a three-stage process is used: in the first stage In, Ga, and Se are deposited simultaneously through crossed-beam coevaporation obtained from separate crucibles on a soda-lime glass substrate coated by a layer of Mo having a thickness of about 1 μ; Cu and Se are deposited in the second stage and In, Ga and Se are lastly deposited again in the third stage. The temperature of the substrate is kept low during the first stage and then it is raised up to about 550°C during the second and the third stage.
The main difficulty of bringing this three-stage process to industrial level lies in the fact that, by using large surface substrates, as required in an industrial process,
the use of crossed-beams leads to the possibility of a composition of the material variable from zone to zone. The non-uniformity of the composition of the material represents, as known, a serious drawback given that it negatively affects the efficiency of the device, not allowing attaining high efficiency. As a matter of fact, given that Cu(ln,Ga)Se2 is a quaternary material, in the areas where there is an excess of Cu, the Cu2Se binary phase can easily form and this, being unstable, frees Cu which causes short circuiting of the device.
An alternative process to the three-stage co-evaporation process has been developed. The alternative process is currently used in various research laboratories and in some industrial laboratories, such as Showa Shell in Japan, Sulfur Cell in Germany and Shell Solar in the United States, and consists in depositing, through sputtering or evaporation, overlapped layers of In, Cu and Ga or an In+Ga alloy on an Mo coated substrate. These layers are first mixed through high temperature annealing and then are subjected to a selenization process in an environment containing Se or H2Se. Given that Ga is less reactive than In, during selenization obtaining a uniformly mixed CulnGaSe2 film requires extremely long annealing time and use of H2Se instead of Se for selenization, in that H2Se is much more reactive than Se.
The aforedescribed process has the drawback of providing for the use of H2Se which is an extremely poisonous gas and which thus requires adopting extremely strict precautions when this gas is used especially at industrial production level.
An atmospheric pressure selenization process is generally described in WO2009034131 .
In WO2009033674 a process for the formation of Cu(ln,Ga)Se2 is disclosed starting from intermetallic precursors which are then converted into semiconductor layers. However, the passage through an intermetallic stage, in the presence of liquid elements (In, Ga), causes stability problems and thus reproducibility problems.
Another known process for the preparation of Cu(ln,Ga)(S,Se2) absorber layers, described in S. Zweigart et al., Proceedings of the First World Conference on Photovoltaic Energy Conversion, (1994), pp 60-67, provides for - as regards the preparation of CulnSe2 - the sequential deposition of InSe and Cu by evaporation followed by selenisation of the double layer of InSe-Cu starting from a room
temperature up to a temperature exceeding 500°C. CulnGaSe2 is obtained by depositing a mixed compound (ln,Ga)(Se,S) on Mo and then the material is selenized or sulphurized during the deposition of Cu. However, even in this case, the final result is not entirely satisfactory in that the CulnSe2 or CulnGaSe2 film which is obtained reveals stoichiometric non-uniformity from one zone to another, i.e. the resulting film is not homogeneous.
Object and summary of the Invention
The aim of the present invention is to provide a method for the preparation of Cu(ln,Ga)Se2 thin films to be used as absorbers in the industrial processes of producing thin-film solar cells of the Cu(ln,Ga)Se2/CdS type.
The process of preparing a Cu(ln,Ga)Se2 thin film according to the present invention provides for the deposition of a Cu-Ga alloy through continuous sputtering on a layer of CulnSe2 and subsequent selenization. In the Cu-Ga alloy, copper may vary from 30 to 70 % atomic and correspondingly gallium from 70 to 30 % atomic, preferably in the process according to the present invention a 50-50 (%) Cu-Ga alloy is used.
The CulnSe2 layer is prepared by successive sputtering deposition on a soda- lime glass layer, coated by a layer of Mo, a layer of ln2Se3 and a layer of Cu, and then progressively heated up to 400-450°C for about 20-30 minutes leaving the materials of the layers to interact with each other for a sufficient period of time (other 20-30 minutes) to form a homogeneous CulnSe2 precursor. The thermal treatment is followed by a step of selenisation under vacuum, at a temperature of 520-550°C and for 5-30 minutes, to complete the amount of Se in the CulnSe2film.
The ln2Se3 target is obtained in polycrystalline form by heating elementary In and Se, in 2 to 6 mm pieces, until the temperature exceeds the melting temperature of ln2Se3 in inert gas atmosphere at low pressure. The use of a ln2Se3 target prepared so as to be in polycrystalline form is deemed very important, in that, if a target obtained through "hot pressing" starting from ln2Se3 powders were used, due to the high vapour tension of Se, discharge instability might occur and, if the cooling is not carried in a very efficient manner, cracks might be formed in the target.
The Mo and Cu targets as well as the Cu-Ga alloy are instead available in the
market, in particular at Testbourne Ltd. (UK).
Detailed description of the Invention
A practical embodiment of the process according to the present invention in described in the following example.
A soda-lime glass with an area measuring 1 inch2 (6.45 cm2) and 4 mm thickness is used as substrate. The substrate is mounted in a sputtering chamber where there are four targets, i.e. Mo, ln2Se3, Cu and a Cu-Ga alloy containing 50% atomic of Cu and 50% atomic of Ga.
The ln2Se3 target was prepared starting from elementary In and Se placed in special graphite or quartz containers and brought to a temperature exceeding the melting temperature of ln2Se3 (890°C). Inert gas, in particular nitrogen, is introduced into the melting furnace at a pressure exceeding 10 atm to avoid the evaporation of the In and Se elements. The target which is thus formed is polycrystalline and it has the same density as the ln2Se3 material.
Deposited in sequence on the substrate in the sputtering chamber are: 1 μηη of
Mo, 1.5 μηη of ln2Se3 and 0.16-0.18 μηη of Cu. Mo and Cu are deposited through continuous sputtering, while ln2Se3 is deposited through radio-frequency sputtering.
The three overlapped Mo-ln2Se3-Cu layers are brought to the temperature of 450°C in about 30 minutes and left to interact with each other for other 30 minutes in a vacuum chamber. This allows forming a CulnSe2 film which however reveals Se deficiency.
In order to obtain the CulnSe2 film having the correct amount of Se, the material is exposed to Se vapour for about 20 minutes, while it is kept at a temperature of 520°C. Selenization is performed in a specially designed vacuum chamber where the substrate is arranged above a crucible containing Se at a distance of a few centimetres.
The selenized CulnSe2 layer is coated by 800 A of Cu-Ga alloy deposited through continuous sputtering and it is selenized again through the procedure described above. The CulnGaSe2 layer thus formed has a Ga content which varies through its thickness, i.e. more Ga is contained at the layer surface than within the layer. This allows the prohibited gap of the material to be larger at the surface than in
the material itself and thus the open circuit potential that can be obtained in the solar cell is higher in the case where Ga is distributed uniformly over the whole material thickness.
Then, 600 A of CdS are deposited on the CulnGaSe2 layer thus formed through radiofrequency sputtering followed by 800 A of pure ZnO and about 1 μηη of ZnO doped with 2% atomic of Al. Pure ZnO is deposited through continuous sputtering from a Zn target in presence of 02 (reactive sputtering), while ZnO(AI) is deposited through continuous sputtering from a ceramic target.
To complete the cell, a grid contact is formed over the ZnO(AI) layer through continuous spluttering.
Devices obtained through the aforedescribed process were tested through a solar simulator having an AM 1 .5 spectrum and a 10OmW/cm2 power. The open circuit potential obtained may vary between 550 and 620 mV, the short circuit current between 32 and 35 mA/cm2 and the fill factor between 0.65 and 0.72 with an average efficiency between 13 and 14%. Solar cells which are normally obtained through processes that use the mixing of elementary layers or indium selenide, gallium and copper compounds, deposited over each other and then selenized, reveal a conversion efficiency of about 12% and they never exceed 13%. Furthermore, the process described herein only uses sputtering and selenization, it neither uses layer evaporation nor any chemical bath which is usually used for preparing CdS film. The use of sputtering alone for deposition all layers facilitates the aligning of the process should it be used for industrial production on a large area of substrate. Furthermore, given the high reproducibility and stability of the sputtering technique, both stoichiometric and thickness uniformity of the layers is guaranteed.
Claims
1 . A process for the preparation of a CulnGaSe2 thin film, usable as absorber layer in CulnGaSe2/CdS solar cells characterized in that said thin film is obtained by sputtering deposition of a Cu-Ga alloy, in which copper may vary from 70 to 30% atomic and correspondingly gallium from 30 to 70% atomic, on a CulnSe2 film deposited on a Mo-coated substrate, and subsequent selenization.
2. The process according to claim 1 , wherein Cu-Ga alloy is deposited by continuous sputtering on the CulnGaSe2 film and the selenization is carried out by exposing the so obtained system to a Se vapour for 5-30 minutes at a temperature of 520-550°C in a vacuum chamber.
3. The process according to claim 2, wherein said CulnSe2 film is obtained by sequential sputtering deposition of ln2Se3 and Cu on said Mo-coated substrate from a polycrystalline ln2Se3 and Cu targets, vacuum annealing and subsequent selenization.
4. The process according to claim 3, wherein ln2Se3 is deposited by RF sputtering, while Cu is deposited by continuous sputtering.
5. The process according to claim 3 or 4, wherein the overlying Mo, ln2Se3 e Cu layers are heated to a temperature of 400-450°C in about 20-30 minutes and kept interacting with one another for other 20-30 minutes and then exposed to Se vapour for 5-30 minutes at a temperature of 520-550°C in a vacuum chamber.
6. The process according to anyone of the previous claims, wherein said ln2Se3 film is deposited from a polycrystalline target obtained by melting In and Se at moderate pressure and inert atmosphere, followed by re-solidification.
7. The process according to claim 6, wherein the pressure is higher than 10 atm.
8. The process according to anyone of the previous claims, wherein said substrate is soda-lime glass and the coating Mo film is deposited by continuous sputtering.
9. The process according to anyone of the previous claims, wherein the CulnGaSe2 layer has a Ga content higher at its surface than at its inside.
10. A process for the production of a CulnGaSe2/CdS thin film solar cell characterized in that it comprises the steps of: a) preparing a CulnGaSe2 absorber film deposited on a Mo-coated substrate according to anyone of the previous claims, and b) depositing by RF sputtering a CdS film on said absorber film.
1 1 . The process according to claim 10, wherein a film of pure ZnO is deposited on the CdS film by continuous sputtering from a Zn target and in the presence of oxygen and subsequently a ZnO(AI) film by continuous sputtering.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ITFI2009A000200A IT1395908B1 (en) | 2009-09-17 | 2009-09-17 | PROCESS FOR THE PRODUCTION OF SOLAR FILMS WITH THIN FILMS CU (IN, GA) SE2 / CDS |
| ITFI2009A000200 | 2009-09-17 |
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| Publication Number | Publication Date |
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| CN114804882A (en) * | 2022-05-24 | 2022-07-29 | 先导薄膜材料（广东）有限公司 | Indium selenide doped target material and preparation method thereof |
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| WO2009033674A2 (en) | 2007-09-11 | 2009-03-19 | Centrotherm Photovoltaics Ag | Method and apparatus for thermally converting metallic precursor layers into semiconducting layers, and also solar module |
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| WO2009033674A2 (en) | 2007-09-11 | 2009-03-19 | Centrotherm Photovoltaics Ag | Method and apparatus for thermally converting metallic precursor layers into semiconducting layers, and also solar module |
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| CN114804882A (en) * | 2022-05-24 | 2022-07-29 | 先导薄膜材料（广东）有限公司 | Indium selenide doped target material and preparation method thereof |
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