# US 2014/0196773 A1 · Multi-junction iii-v solar cell

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- Number: US 2014/0196773 A1
- Document ID: US20140196773A1
- Status: Published application
- Kind: A1
- Application number: 13/738,989
- Filed: 2013-01-11
- Published: 2014-07-17
- Earliest claimed: 2013-01-11
- Assignees: International Business Machines Corporation
- Applicants: International Business Machines Corp
- Inventors: Stephen W. Bedell; Bahman Hekmatshoartabari; Devendra K. Sadana; Ghavam G. Shahidi; Davood Shahrjerdi
- Web page: https://patentgrep.com/patent/US20140196773A1

## CPC

- H10F 10/161: comprising multiple PN heterojunctions, e.g. tandem cells
- H10F 10/163: comprising only Group III-V materials, e.g. GaAs/AlGaAs or InP/GaInAs photovoltaic cells
- H10F 10/19: Photovoltaic cells having multiple potential barriers of different types, e.g. tandem cells having both PN and PIN junctions
- Y02E 10/50: Photovoltaic [PV] energy
- Y02E 10/544: Solar cells from Group III-V 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 multi junction solar cell structure includes a top photovoltaic cell including III-V semiconductor materials and a silicon-based bottom photovoltaic cell. A thin, germanium-rich silicon germanium buffer layer is provided between the top and bottom cells. Fabrication techniques for producing multi junction III-V solar cell structures, lattice-matched or pseudomorphic to germanium, on silicon substrates is further provided wherein silicon serves as the bottom cell. The open circuit voltage of the silicon cell may be enhanced by localized back surface field structures, localized back contacts, or amorphous silicon-based heterojunction back contacts.

## Claims

### Claim at position 1

-15. (canceled)

### Claim 16

A method comprising:
obtaining a bottom photovoltaic structure comprising a crystalline silicon base and an emitter layer comprising silicon on the base;
forming a first buffer layer on the bottom photovoltaic structure, the first buffer layer including a first portion comprising silicon and germanium and a second, germanium-rich portion having a substantially greater percentage of germanium than the first portion;
forming a tunnel junction over the first buffer layer, and
forming a top photovoltaic cell having a bandgap between 1.8-2.1 eV over the tunnel junction and lattice matched or pseudomorphic to the germanium-rich portion of the buffer layer, the top photovoltaic cell including a first base layer and a first emitter layer adjoining the first base layer, the first base and emitter layers each being comprised of a III-V semiconductor material.

### Claim 17 (depends on 16)

The method of claim 16, wherein the step of forming the first buffer layer further includes forming the first portion of the buffer layer as the emitter layer of the bottom photovoltaic structure.

### Claim 18 (depends on 16)

The method of claim 16, wherein the step of forming the first buffer layer includes forming the second, germanium-rich portion such that germanium comprises substantially one hundred percent of the second portion.

### Claim 19 (depends on 16)

The method of claim 16, further including forming a second buffer layer comprised of III-V semiconductor material and effective for avoiding antiphase boundary defects, between the first buffer layer and the tunnel junction.

### Claim 20 (depends on 19)

The method of claim 19, further including forming a bottom contact layer that contacts the crystalline silicon base of the bottom photovoltaic structure at a plurality of discrete areas.

### Claim 21 (depends on 20)

The method of claim 20, further comprising forming a plurality of highly doped regions in the crystalline silicon base of the bottom photovoltaic structure, the highly doped regions comprising a localized back surface field structure contacting the bottom contact layer at the plurality of discrete areas.

### Claim 22 (depends on 19)

The method of claim 19, further including forming a back surface field adjoining the second base layer, wherein the back surface field comprises a heterojunction.

### Claim 23 (depends on 19)

The method of claim 19, wherein the first buffer layer is formed to a thickness of less than 0.5 μm.

### Claim at position 10

24-25. (canceled)