# US 9,520,530 B2 · Solar cell having doped buffer layer and method of fabricating the solar cell

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- Number: US 9,520,530 B2
- Document ID: US9520530B2
- Status: Granted
- Kind: B2
- Application number: 14/505,534
- Filed: 2014-10-03
- Published: 2016-04-07
- Granted: 2016-12-13
- Earliest claimed: 2014-10-03
- Assignees: Taiwan Semiconductor Manufacturing Company, Ltd.
- Applicants: TSMC Solar Ltd.
- Inventors: Jyh-Lih Wu
- Web page: https://patentgrep.com/patent/US9520530B2

## CPC

- H10F 71/128: {Annealing}
- H10F 10/16: Photovoltaic cells having only PN heterojunction potential barriers
- H10F 10/167: comprising Group I-III-VI materials, e.g. CdS/CuInSe2 [CIS] heterojunction photovoltaic cells
- H10F 10/169: {comprising Cu2X/CdX heterojunctions, wherein X is a Group VI element, e.g. Cu2O/CdO PN heterojunction photovoltaic cells}
- H10F 71/125: {The active layers comprising only Group II-VI materials, e.g. CdS, ZnS or CdTe}
- H10F 71/1253: {comprising at least three elements, e.g. HgCdTe}
- H10F 71/138: {Manufacture of transparent electrodes, e.g. transparent conductive oxides [TCO] or indium tin oxide [ITO] electrodes}
- H10F 77/126: {comprising only Group I-III-VI chalcopyrite materials, e.g. CuInSe2, CuGaSe2 or CuInGaSe2 [CIGS]}
- H10F 77/127: {comprising only Group IV-VI or only Group II-IV-VI chalcogenide materials, e.g. PbSnTe}
- H10F 77/219: {Arrangements for electrodes of back-contact photovoltaic cells}
- H10F 77/244: {made of transparent conductive layers, e.g. transparent conductive oxide [TCO] layers}
- Y02E 10/541: CuInSe2 material PV cells
- Y02E 10/543: Solar cells from Group II-VI materials
- 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
- 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 method includes: forming a buffer layer over an absorber layer of a photovoltaic device; and extrinsically doping the buffer layer after the forming step.

## Claims

### Claim 1

A method comprising:
forming a single buffer layer of a CdS material directly on an absorber layer of a photovoltaic device using a single non-chemical-bath-deposition process;
extrinsically doping the single buffer layer in a chamber after the forming step, with a dopant having a concentration that varies between a top surface of the single buffer layer and an interface between the single buffer layer and the absorber layer; and
forming a front contact layer of a second material directly on the single buffer layer in the same chamber, the CdS material extending from the interface between the buffer layer and the absorber layer to an interface between the buffer layer and the front contact layer, the second material having a different composition from the CdS material.

### Claim 2 (depends on 1)

The method of claim 1, wherein the step of extrinsically doping the buffer layer includes annealing the buffer layer.

### Claim 3 (depends on 1)

The method of claim 1, wherein the step of extrinsically doping the buffer layer includes annealing the buffer layer in an atmosphere comprising a dopant.

### Claim 4 (depends on 3)

The method of claim 3, wherein the atmosphere comprises at least one of the group consisting of boron (B), aluminum (Al), gallium (Ga), indium (In), or combinations thereof.

### Claim 5 (depends on 3)

The method of claim 3, wherein the atmosphere comprises B2H6.

### Claim 6 (depends on 3)

The method of claim 3, wherein the annealing is performed at a temperature in a range from about 70° C. to about 400° C.

### Claim 7 (depends on 6)

The method of claim 6, wherein the annealing is performed at about 170° C. for about 10 minutes.

### Claim 8 (depends on 1)

The method of claim 1, wherein the step of forming the front contact layer comprises metal organic chemical vapor deposition.

### Claim 9

A method comprising:
forming a single buffer layer of a first CdS material directly on an absorber layer of a photovoltaic device by a non-chemical-bath-deposition (CBD) process from the group consisting of atomic layer deposition, sputtering, electro-deposition, evaporation or chemical vapor deposition;
extrinsically doping the single buffer layer in a metal organic chemical vapor deposition (MOCVD) chamber; and
forming a front contact layer of a second material directly on the single buffer layer in the same MOCVD chamber, the CdS material extending from an interface between the buffer layer and the absorber layer to an interface between the buffer layer and the front contact layer, the second material having a different composition from the CdS material.

### Claim 10 (depends on 9)

The method of claim 9, wherein the step of extrinsically doping the buffer layer includes annealing the buffer layer.

### Claim 11 (depends on 9)

The method of claim 9, wherein the step of extrinsically doping the buffer layer includes annealing the buffer layer in an atmosphere comprising a dopant.

### Claim 12 (depends on 11)

The method of claim 11, wherein the atmosphere comprises B2H6.

### Claim 13 (depends on 12)

The method of claim 12, wherein the annealing is performed at about 170° C. for about 10 minutes.

### Claim 14 (depends on 9)

The method of claim 9 wherein the step of forming the front contact layer comprises metal organic chemical vapor deposition.

### Claim 15 (depends on 9)

The method of claim 9, further comprising forming a front contact layer over the buffer layer, wherein:
the steps of extrinsically doping the buffer layer and forming the front contact layer are both performed in a same chamber;
the step of extrinsically doping the buffer layer includes annealing the buffer layer in an atmosphere comprising B2H6 at about 170° C. for about 10 minutes; and
the step of forming the front contact layer comprises metal organic chemical vapor deposition.

### Claim 16 (depends on 15)

The method of claim 15, further comprising:
forming a back contact of molybdenum over a substrate comprising glass, plastic or a metal foil;
forming the absorber over the back contact, where the absorber comprises at least one of the group consisting of copper (Cu), gallium (Ga), indium (In), aluminum (Al), selenium (Se), sulfur (S), or combinations thereof.

### Claim 17

A method comprising:
forming a single buffer layer of CdS directly on an absorber layer of a photovoltaic device;
annealing the single buffer layer in a metal organic chemical vapor deposition (MOCVD) chamber having an atmosphere containing B2H6 after the forming step, so as to have a higher concentration of boron dopant at a top surface of the single buffer layer than at an interface between the single buffer layer and the absorber layer; and
forming a front contact layer of a transparent conductive oxide directly on the single buffer layer in the same MOCVD chamber where the annealing is performed, so the CdS extends from the interface between the buffer layer and the absorber layer to an interface between the buffer layer and the front contact layer.

### Claim 18 (depends on 17)

The method of claim 17, wherein:
the buffer layer is annealed at about 170° C. for about 10 minutes, and
the step of forming the front contact layer comprises metal organic chemical vapor deposition.

### Claim 19 (depends on 1)

The method of claim 1, wherein the doping increases the concentration in the single buffer layer at an interface between the single buffer layer and the absorber layer.