# US 2013/0157408 A1 · Absorber layer for a thin film photovoltaic device with a double-graded band gap

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- Number: US 2013/0157408 A1
- Document ID: US20130157408A1
- Status: Published application
- Kind: A1
- Application number: 13/331,793
- Filed: 2011-12-20
- Published: 2013-06-20
- Earliest claimed: 2011-12-20
- Assignees: Intermolecular, Inc.
- Inventors: Haifan Liang
- Web page: https://patentgrep.com/patent/US20130157408A1

## CPC

- H10F 71/128: {Annealing}
- H10F 10/13: Photovoltaic cells having absorbing layers comprising graded bandgaps
- H10F 10/167: comprising Group I-III-VI materials, e.g. CdS/CuInSe2 [CIS] heterojunction photovoltaic cells
- H10F 77/126: {comprising only Group I-III-VI chalcopyrite materials, e.g. CuInSe2, CuGaSe2 or CuInGaSe2 [CIGS]}
- H10P 14/22: using physical deposition, e.g. vacuum deposition or sputtering
- H10P 14/24: using chemical vapour deposition [CVD]
- H10P 14/2922: {being non-crystalline insulating materials, e.g. glass or polymers}
- H10P 14/2923: {being conductive materials, e.g. metallic silicides}
- H10P 14/3236: {being chalcogenide semiconducting materials not being oxides, e.g. ternary compounds}
- H10P 14/3254: {Graded layers}
- H10P 14/3436: {being chalcogenide semiconductor materials not being oxides, e.g. ternary compounds}
- H10P 14/3444: {P-type}
- Y02E 10/541: CuInSe2 material PV cells
- Y02P 70/50: Manufacturing or production processes characterised by the final manufactured product
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A gallium-containing alloy is formed on the light-receiving surface of a CIGS absorber layer, and, in conjunction with a subsequent selenization or anneal process, is converted to a gallium-rich region at the light-receiving surface of the CIGS absorber layer. A second gallium-rich region is formed at the back contact surface of the CIGS absorber layer during selenization, so that the CIGS absorber layer has a double-graded gallium concentration that increases toward the light-receiving surface and toward the back contact surface of the CIGS absorber layer. The double-graded gallium concentration advantageously produces a double-graded bandgap profile for the CIGS absorber layer.

## Claims

### Claim 1

A method of forming a thin-film solar cell absorber layer, the absorber layer having a surface that is light receiving, the method comprising:
forming a first layer on a substrate, the layer comprising copper, indium, and gallium;
forming a second layer above the first layer, the second layer comprising gallium (Ga) and selenium (Se); and
heating the second layer to convert the second layer to a gallium rich region at the light receiving surface of the absorber layer,
wherein the step of forming the second layer is at a lower temperature than the step of heating the second layer.

### Claim 2 (depends on 1)

The method of claim 1, wherein forming the second layer on the first layer comprises exposing the first layer to trimethyl gallium (TMGa) and a selenium-containing gas.

### Claim 3 (depends on 1)

The method of claim 1, wherein forming the second layer comprises maintaining the substrate at a temperature between about 20° C. and about 350° C.

### Claim 4 (depends on 3)

The method of claim 3, wherein the selenium-containing gas comprises hydrogen selenide (H2Se).

### Claim 5 (depends on 1)

The method of claim 1, wherein the step of heating is performed at a temperature between about 400° C. and about 550° C.

### Claim 6 (depends on 1)

The method of claim 1, wherein the step of forming the second layer and the step of heating the second layer are performed in the same reaction chamber.

### Claim 7 (depends on 1)

The method of claim 1, further comprising adjusting a distribution of gallium in the gallium-rich region and in the first layer by annealing the gallium-rich region and the first layer at a temperature greater than or equal to about 500° C.

### Claim 8 (depends on 1)

The method of claim 1, wherein the step of heating the second layer comprises performing a selenization process.

### Claim 9

A method of forming a thin-film solar cell absorber layer, the absorber layer having a first surface that is light receiving, the method comprising:
forming a first layer on a substrate, wherein the first layer comprises copper, indium, gallium, and selenium and includes a gallium-rich region;
exposing the first layer to trimethyl gallium (TMGa) and a selenium-containing gas to form a second layer above the first layer, wherein the second layer comprises gallium (Ga) and selenium (Se); and
heating the second layer to convert the second layer to a gallium rich region at the light receiving surface of the absorber layer.

### Claim 10 (depends on 9)

The method of claim 9, further comprising, prior to forming the second layer above the first layer, heating the substrate to form a gallium-rich region at a second surface of the absorber layer, wherein the second surface is disposed opposite the first surface.

### Claim 11 (depends on 10)

The method of claim 10, wherein the second surface is adjacent to a back contact layer of the thin-film solar cell.

### Claim 12 (depends on 10)

The method of claim 10, wherein the step of heating the substrate prior to forming the second layer above the first layer comprises a selenization process.

### Claim 13 (depends on 9)

The method of claim 9, wherein the step of exposing the first layer to TMGa and the selenium-containing gas and the step of heating the second layer are performed in the same reaction chamber.

### Claim 14 (depends on 9)

The method of claim 9, further comprising heating the first layer and the gallium-rich region to a temperature between about 500° C. and about 600° C.

### Claim 15

A method of forming a thin-film solar cell absorber layer, the absorber layer having a first surface that is light receiving, the method comprising:
forming a first layer on a substrate, wherein the first layer comprises copper, indium, gallium, and selenium and includes a gallium-rich region;
forming a second layer above the first layer via thermal pyrolysis of trimethyl gallium (TMGa);
exposing the second layer to heat and a selenium-containing gas to convert the second layer to a third layer that comprises gallium (Ga) and selenium (Se); and
heating the third layer to convert the third layer to a gallium rich region at the light receiving surface of the absorber layer.

### Claim 16 (depends on 15)

The method of claim 15, wherein the step of forming a first layer on a substrate, the step of forming a second layer above the first layer, and the step of heating the third layer are performed in the same reaction chamber.

### Claim 17 (depends on 15)

The method of claim 15, wherein the step of exposing the second layer comprises heating the substrate to a temperature between about 400° C. and about 500° C. and exposing the second layer to hydrogen selenide (H2Se) gas.

### Claim 18 (depends on 15)

The method of claim 15, further comprising, prior to forming the second layer above the first layer, performing a selenization process on a copper-indium-gallium layer to form the first layer and to form the gallium-rich region at a second surface of the absorber layer, wherein the second surface is opposite the first surface.

### Claim 19 (depends on 15)

The method of claim 15, wherein the step of forming the second layer is performed at a temperature between about 450° C. and 500° C.

### Claim 20 (depends on 15)

The method of claim 15, wherein the step of exposing the second layer comprises performing a selenization process.