# US 2014/0196774 A1 · Multi-junction iii-v solar cell

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- Number: US 2014/0196774 A1
- Document ID: US20140196774A1
- Status: Published application
- Kind: A1
- Application number: 13/970,334
- Filed: 2013-08-19
- Published: 2014-07-17
- Earliest claimed: 2013-01-11
- Assignees: International Business Machines Corporation
- Applicants: International Business Machines Corporation
- Inventors: Stephen W. Bedell; Bahman Hekmatshoartabari; Devendra K. Sadana; Ghavam G. Shahidi; Davood Shahrjerdi
- Web page: https://patentgrep.com/patent/US20140196774A1

## 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 1

A multi junction solar cell structure comprising:
a top photovoltaic cell having a bandgap between 1.8-2.1 eV, 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;
a bottom photovoltaic cell including a second base layer and a second emitter layer adjoining the second base layer, the second base and emitter layers each being comprised of silicon;
a buffer layer between the top and bottom photovoltaic cells, the buffer layer comprising silicon and germanium and having a germanium-rich portion, the top photovoltaic cell being lattice matched or pseudomorphic to the germanium-rich portion of the buffer layer, and
a tunnel junction between the top photovoltaic cell and the buffer layer.

### Claim 2 (depends on 1)

The structure of claim 1, further comprising a first contact layer in electrical communication with the top photovoltaic cell and a second contact layer in electrical communication with the bottom photovoltaic cell.

### Claim 3 (depends on 2)

The structure of claim 2, wherein the second contact layer contacts the second base layer of the bottom cell at a plurality of discrete areas, further comprising a passivating layer between the second contact layer and the second base layer.

### Claim 4 (depends on 3)

The structure of claim 3, further comprising a plurality of highly doped regions in the second base layer, the highly doped regions comprising a localized back surface field structure contacting the second contact layer at the plurality of discrete areas.

### Claim 5 (depends on 1)

The structure of claim 1, further including a back surface field adjoining the second base layer.

### Claim 6 (depends on 5)

The structure of claim 5, wherein the back surface field comprises a heterojunction.

### Claim 7 (depends on 6)

The structure of claim 6, wherein the back surface field comprises a hydrogenated amorphous silicon layer.

### Claim 8 (depends on 1)

The structure of claim 1, wherein the buffer layer has a thickness of less than 0.5 μm.

### Claim 9 (depends on 1)

The structure of claim 1, wherein the buffer layer includes a textured surface.

### Claim 10 (depends on 1)

The structure of claim 1, wherein the top photovoltaic cell has a thickness of less than 1.5 μm.

### Claim 11 (depends on 1)

The structure of claim 1, further including a second buffer layer between the buffer layer comprising silicon and germanium and the tunnel junction, the second buffer layer being comprised of III-V semiconductor material and effective for avoiding antiphase boundary defects.

### Claim 12 (depends on 11)

The structure of claim 11, wherein the base layer of the bottom photovoltaic cell is comprised of p-type crystalline silicon.

### Claim 13 (depends on 12)

The structure of claim 12, wherein the buffer layer comprising silicon and germanium has a thickness of less than 0.5 μm.

### Claim 14 (depends on 13)

The structure of claim 13, wherein the buffer layer comprising silicon and germanium is comprised of a SiGe portion adjoining the second emitter layer, the germanium-rich portion thereof comprising substantially one hundred percent germanium, and the first base layer of the top photovoltaic cell is comprised of p-InGaP, p-InGaAlP, or p-AlGaAs.

### Claim 15 (depends on 13)

The structure of claim 13, wherein the buffer layer comprising silicon and germanium includes a first SiGe portion adjoining the second emitter layer and the germanium-rich portion, the germanium-rich portion being comprised of at least ninety percent germanium, the germanium-rich portion being comprised of a substantially greater percentage of germanium than the first SiGe portion, the thickness of the germanium-rich portion of the buffer layer exceeding the thickness of the first SiGe portion thereof.

### Claim 16

A multi junction solar cell structure comprising:
a top photovoltaic cell having a bandgap between 1.8-2.1 eV, 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;
a bottom photovoltaic cell including a crystalline silicon second base layer and a second emitter layer adjoining the second base layer;
a first buffer layer having a thickness of less than 0.5 μm between the top and bottom photovoltaic cells, the first buffer layer including a silicon germanium portion adjoining the bottom photovoltaic cell and a germanium-rich portion comprising at least ninety percent germanium, the top photovoltaic cell being lattice-matched or pseudomorphic to the germanium-rich portion of the first buffer layer;
a tunnel junction between the first buffer layer and the top photovoltaic cell, and
a second buffer layer between the first buffer layer and the tunnel junction, the second buffer being effective for avoiding antiphase boundary defects.

### Claim 17 (depends on 16)

The structure of claim 16, wherein a majority of the thickness of the first buffer layer is comprised of the germanium-rich portion, the germanium-rich portion comprising substantially one hundred percent germanium, the top photovoltaic cell being lattice-matched to germanium.