# US 11,444,215 B2 · Double layered transparent conductive oxide for reduced Schottky barrier in photovoltaic devices

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- Number: US 11,444,215 B2
- Document ID: US11444215B2
- Status: Granted
- Kind: B2
- Application number: 16/741,142
- Filed: 2020-01-13
- Published: 2020-05-14
- Granted: 2022-09-13
- Earliest claimed: 2012-11-05
- Assignees: International Business Machines Corporation; Bay Zu Precision Co., Ltd.
- Applicants: International Business Machines Corporation; Bay Zu Precision Co., LTD.
- Inventors: Shun-Ming Chen; Chien-Chih Huang; Joel P. Desouza; Augustin J. Hong; Jeehwan Kim; Chien-Yeh Ku; Devendra K. Sadana; Chuan-Wen Wang
- Web page: https://patentgrep.com/patent/US11444215B2

## CPC

- H10F 77/251: {comprising zinc oxide [ZnO]}
- H10F 10/17: Photovoltaic cells having only PIN junction potential barriers
- H10F 71/138: {Manufacture of transparent electrodes, e.g. transparent conductive oxides [TCO] or indium tin oxide [ITO] electrodes}
- H10F 77/1692: {the films including only Group IV materials}
- H10F 77/211: {for photovoltaic cells}
- Y02E 10/547: Monocrystalline silicon PV cells
- Y02E 10/548: Amorphous silicon PV cells
- 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

## Abstract

A device and method for fabricating a photovoltaic device includes forming a double layer transparent conductive oxide on a transparent substrate. The double layer transparent conductive oxide includes forming a doped electrode layer on the substrate, and forming a buffer layer on the doped electrode layer. The buffer layer includes an undoped or p-type doped intrinsic form of a same material as the doped electrode layer. A light-absorbing semiconductor structure includes a p-type semiconductor layer on the buffer layer, an intrinsic layer and an n-type semiconductor layer.

## Claims

### Claim 1

A method for fabricating a photovoltaic device, comprising:
forming a double layer transparent conductive oxide on a transparent substrate including:
forming a doped electrode layer on the substrate; and
forming a buffer layer on the doped electrode layer by reducing dopant concentration to zero, the buffer layer comprising an oppositely doped form of a same material as the doped electrode layer, and including a different doping concentration than the doped electrode layer; and
forming a light-absorbing semiconductor structure.

### Claim 2 (depends on 1)

The method as recited in claim 1, wherein forming a buffer layer includes forming the buffer layer with a work function having a value between values of work functions of adjacent layers.

### Claim 3 (depends on 1)

The method as recited in claim 1, wherein the doped electrode layer and the buffer layer include ZnO.

### Claim 4 (depends on 1)

The method as recited in claim 1, wherein the buffer layer includes a thickness between about 100 nm and 500 nm.

### Claim 5 (depends on 1)

The method as recited in claim 1, further comprising forming a second electrode on the light-absorbing semiconductor structure.

### Claim 6 (depends on 1)

The method as recited in claim 1, wherein the light absorbing semiconductor structure includes a p-type semiconductor layer on the buffer layer, an intrinsic layer, and an n-type semiconductor layer, the p-type semiconductor layer comprising at least one of Si and SiC.

### Claim 7 (depends on 1)

The method as recited in claim 1, further comprising texturing the double layer to provide a three-dimensional structure.

### Claim 8 (depends on 1)

The method as recited in claim 1, wherein the buffer layer includes p-type dopants increasing in concentration from the doped electrode layer.

### Claim 9 (depends on 1)

The method as recited in claim 1, wherein the buffer layer includes n-type dopants decreasing in concentration from the doped electrode layer.

### Claim 10

A method for fabricating a photovoltaic device, comprising:
forming a double layer transparent conductive oxide on a transparent substrate including:
sputtering on a doped electrode layer on the substrate using a first target source;
switching to a second target source in-situ, wherein the photovoltaic device being fabricated remains in a same processing chamber for formation of the entire double layer;
sputtering on a buffer layer comprising an oppositely doped form of a same material as the doped electrode layer on the doped electrode layer using the second target source, the buffer layer including a different doping concentration than the doped electrode layer; and
forming a light-absorbing semiconductor structure.

### Claim 11 (depends on 10)

The method as recited in claim 10, wherein forming a buffer layer includes forming the buffer layer with a work function having a value between values of work functions of adjacent layers.

### Claim 12 (depends on 10)

The method as recited in claim 10, wherein the doped electrode layer and the buffer layer include ZnO.

### Claim 13 (depends on 10)

The method as recited in claim 10, wherein the buffer layer includes a thickness between about 100 nm and 500 nm.

### Claim 14 (depends on 10)

The method as recited in claim 10, further comprising forming a second electrode on the light-absorbing semiconductor structure.

### Claim 15 (depends on 10)

The method as recited in claim 10, wherein the light absorbing semiconductor structure includes a p-type semiconductor layer on the buffer layer, an intrinsic layer, and an n-type semiconductor layer, the p-type semiconductor layer comprising at least one of Si and SiC.

### Claim 16 (depends on 10)

The method as recited in claim 10, further comprising forming a textured surface on the doped electrode layer.

### Claim 17 (depends on 16)

The method as recited in claim 16, wherein forming a textured surface includes wet etching the doped electrode layer to form pyramidal structures.

### Claim 18 (depends on 10)

The method as recited in claim 10, wherein the buffer layer includes p-type dopants increasing in concentration from the doped electrode layer.

### Claim 19 (depends on 10)

The method as recited in claim 10, wherein the buffer layer includes n-type dopants decreasing in concentration from the doped electrode layer.

### Claim 20

A method for fabricating a photovoltaic device, comprising:
forming a double layer transparent conductive oxide on a transparent substrate including:
depositing a doped electrode layer on the substrate using a low pressure chemical vapor deposition (LPCVD) process;
forming a buffer layer comprising an oppositely doped form of a same material as the doped electrode layer on the doped electrode layer using the LPCVD process by reducing dopant concentration to zero, the buffer layer including a different doping concentration than the doped electrode layer; and
forming a light-absorbing semiconductor structure.