GB2370282A - Anodic process for producing chalcopyrite compounds - Google Patents

Abstract

A multiple step process to produce chalcopyrite compounds of the type, Cu(In<SB>x</SB> Ga<SB>1-x</SB>)( Sy Se<SB>1-y</SB>)<SB>2</SB>, (e.g. CuInS<SB>2</SB> or CuInSe<SB>2</SB>) involves depositing precursor layers of the metallic elements as stacked elemental layers or alloys of the elements followed by electrochemical conversion of the precursor layers into the chalcopyrite compound or alloy. The process involves the anodic sulphidisation or selenisation of the layers by passing an electric current through a solution of selenide/sulphide salts dissolved in an aqueous alkaline or neutral solution or an organic solvent. Annealing is used to complete the chemical reaction(s) to form the chalcopyrite compound and to improve the physical properties of the layers.

Description

Rapid Anodic Process for Producing ! Chalcopyrite Compounds This invention relates to a novel method for producing thin film chalcopyrite

semiconductors of the type Cu (InxGa l-x) (SySe i-y, e. g. CuInSe2 and Cuis2, which find k-y) 27 application in thin film solar cell devices.

Photovoltaic solar cells consist of a junction between a n-type and p-type semiconductor and use the phenomenon known as the photovoltaic effect for directly converting sunlight into electricity. The p-type semiconductor has an energy bandgap appropriate for absorbing incident solar radiation and it hence has an energy bandgap in the range 1. 0-1 7 eV ; it is referred to as the"absorber layer"in a solar cell. The n-type layer forms the p-n junction with the absorber layer and it must allow light to pass through it to the absorber layer; the wider energy bandgap, transmissive n-type layer is referred to as the"window layer"in a solar cell structure. In some devices a thin"buffer layer"is included between the n and p-type layers to improve the junction properties.

The most advanced methods to produce chalcopyrite thin films for use as"absorber layers"in thin film solar cells involve a two step process: 1. the formation of Cu/In/Ga precursor layers by co-evaporation, sputtering electrodeposition or electroless deposition or by annealing alternate Cu/In/Ga layers deposited using these methods, 2. annealing the precursor layers in a H2Se or selenium environment to form the chalcopyrite selenide or in a H2S or sulphur environment to form the chalcopyrite sulphide.

The latter annealing step involves heating the metallic precursors in environments containing highly toxic/corrosive gases.

This patent gives a novel process for producing chalcopyrite selenides and sulphides that is safer than the conventional method and also minimises the use of expensive vacuum technology.

The process is similar to the conventional method in that the first step is the formation of Cu/In/Ga precursor layers by co-evaporation, sputtering, electrodeposition or electroless deposition or by annealing alternate Cu/In/Ga layers deposited using these methods. The innovative step is the combination of this first step with anodic selenisation or sulphurisation to convert the layers into chalcopyrite selenides and sulphides.

The electrolyte used is a solution of a sulphide or selenide in an alkaline aqueous solvent, e. g. a solution of potassium or sodium hydroxide or an inorganic solvent such as ethylene glycol. Typical solutes are Na2S, Nits, Na2Se or NH4Se. The sodium salts are preferred because sodium ions play a role in passivating the grain boundaries in the synthesised layers. The precursor layers form the conducting anode. The other electrode (s) can be made from a wide range of materials, e. g. platinum.

The layers may then be annealed to complete the reaction between the precursor layer and the sulphur/selenium incorporated and to improve the grain size and other physical properties.

Typical Steps Taken to Fabricate a Chalcoovite-Based Thin Film Solar Cell, (Substrate Configuration).

Step 1 deposition of a back contact material onto a substrate, e. g. molydenum onto glass.

Step 2: deposition of the Cu/In/Ga precursor layers onto the molydenum coated glass substrates.

Step 3 selenisation/sulphurisation of the precursor layers using the anodic process given in this patent application.

Step 4: annealing.

Step 5: etching to remove binary sulphides using e. g. potassium cyanide.

Step 6: deposition of"buffer layer"., e. g. CdS, ZnS or ZnSe or alloys of these materials with (OH) groups.

Step 7: deposition of wide bandgap window layer, e. g. CdS, ZnO, ZnSe, SnO2 or indium tin oxide.

Step 8: deposition of a contact grid.

Step 9: anneal.

Tvoicai Steps Taken to Fabricate a Chalcopyrite -Based Thin Film Solar Cell.

(Superstrate Configuration) Step 1: deposit buffer layer onto tin oxide coated glass, e. g. ZnS.

Step 2: deposit precursor layers onto the buffer layer.

Step 3: anodically sulphidise/selenise.

Step 4: anneal.

Step 5: deposit back contact.

Step 6: anneal.

Claims (3)

1. CLAIMS 1. The process of production of chalcopyrite selenide compounds and alloys, e. g.

   CuInSe2 or CuGaInSe2, by the multiple-step process, deposition of stacked elemental layers of the metals or an alloy of the metals followed by anodic selenisation to form the compound/alloy.
2. 2. The process of production of chalcopyrite sulphide compounds and alloys, e. g.

   CuInS2 or CuGaInS2, by the multiple-step process, deposition of stacked elemental layers of the metals or an alloy of the metals followed by anodic sulphurisation to form the compound/alloy.
3. 3. The process of production of chalcopyrite selenide/sulphide alloys, e. g.

   CuIn (Sel, S.) 2 by the multiple-step process, deposition of stacked elemental layers of the metals or an alloy of the metals followed by anodic selenisation/sulphurisation to form the compound/alloy.