# US 8,772,628 B2 · High performance, high bandgap, lattice-mismatched, GaInP solar cells

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- Number: US 8,772,628 B2
- Document ID: US8772628B2
- Status: Granted
- Kind: B2
- Application number: 12/992,871
- Filed: 2009-01-29
- Published: 2011-08-04
- Granted: 2014-07-08
- Earliest claimed: 2004-12-30
- Assignees: Alliance for Sustainable Energy, LLC
- Applicants: Mark W. Wanlass; Jeffrey J. Carapella; Myles A. Steiner
- Inventors: Mark W. Wanlass; Jeffrey J. Carapella; Myles A. Steiner
- Web page: https://patentgrep.com/patent/US8772628B2

## CPC

- H10F 10/13: Photovoltaic cells having absorbing layers comprising graded bandgaps
- H10F 10/14: Photovoltaic cells having only PN homojunction potential barriers
- H10F 10/1425: {Inverted metamorphic multi-junction [IMM] photovoltaic cells}
- H10F 10/144: comprising only Group III-V materials, e.g. GaAs,AlGaAs, or InP photovoltaic cells
- H10F 71/1272: {comprising at least three elements, e.g. GaAlAs or InGaAsP}
- H10F 71/139: {using temporary substrates}
- H10F 77/12: Active materials
- H10F 77/211: {for photovoltaic cells}
- H10F 77/315: {the coatings being antireflective or having enhancing optical properties}
- Y02E 10/544: Solar cells from Group III-V materials
- Y02E 10/547: Monocrystalline 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

High performance, high bandgap, lattice-mismatched, photovoltaic cells (10), both transparent and non-transparent to sub-bandgap light, are provided as devices for use alone or in combination with other cells in split spectrum apparatus or other applications.

## Claims

### Claim 1

A method of fabricating a high bandgap GaInP photovoltaic converter, comprising:
providing a crystalline growth structure having a growth surface that has a lattice constant which matches a relaxed lattice constant of a GaInP alloy that has a bandgap greater than that of Ga0.51In0.49P, wherein the crystalline growth structure comprises a graded GaAsP structure with a base surface having a lattice constant matching that of GaAs and where the growth surface comprises a GaAs1-xPx alloy;
growing a front contact layer on the growth surface;
growing a GaInP photovoltaic cell on the front contact layer, the GaInP photovoltaic cell having a relaxed lattice constant matching the lattice constant of the growth surface; and
growing a back contact layer on the GaInP photovoltaic cell.

### Claim 2 (depends on 1)

The method of claim 1, wherein the front contact layer is a doped GaAsP front contact layer, the method further including:
doping the GaAsP front contact layer as a n-type dopant for an emitter in the GaInP cell, growing an initial thickness of the GaInP cell with no dopant, and growing the remainder of the GaInP cell with a p-type dopant to form a base portion of the GaInP cell while allowing the n-type dopant diffuse from the GaAsP front contact layer into the undoped thickness of the GaInP cell to form an emitter portion of the GaInP cell.

### Claim 3 (depends on 2)

The method of claim 2, including growing the GaInP cell in a process that involves an elevated temperature sufficiently high to induce the diffusion of the dopant from the GaAsP front contact layer into the GaInP cell.

### Claim 4 (depends on 3)

The method of claim 3, wherein the elevated temperature is in a range of about 600-750° C.

### Claim 5 (depends on 2)

The method of claim 2, including doping only a portion of the GaAsP front contact layer with the n-type dopant for the GaInP, said portion of the GaAsP being a spaced distance away from the base portion.

### Claim 6 (depends on 1)

The method of claim 1, wherein providing the crystalline growth structure further comprises:
growing a graded layer of GaAs1-xPx on a crystalline parent substrate by starting the GaAs1-xPx the graded layer with a value of “x” that proportions the As and P in the GaAs1-xPx in a manner that provides the GaAs1-xPx with a lattice constant that matches the lattice constant of the parent substrate and ends with a value of “x” that proportions the Ga and P in the GaAs1-xPx in a manner that provides the GaAs1-xPx with a growth plane lattice constant that matches a relaxed lattice constant of GaInP with a target bandgap between about 1.9 eV and 2.2 eV.

### Claim 7 (depends on 6)

The method of claim 6, wherein the parent substrate is GaAs.

### Claim 8 (depends on 7)

The method of claim 7, wherein the graded GaAs1-xPx comprises 6 to 10 steps of GaAs1-xpx, each step being about 1.0 to 2.2 μm thick, with the phosphorus content increased, and the As content correspondingly decreased, by approximately 4 to 6 percent per step, and with the last step being approximately 30 to 44 percent phosphorus,

### Claim 9 (depends on 6)

The method of claim 6, wherein the front contact layer is a doped GaAsP front contact layer and the back contact layer is a doped GaAsP back contact layer, the method further including:
growing a front passivation/window layer between the doped GaAsP front contact layer and an emitter of the GaInP cell and growing a back side confinement layer between a base of the GaInP cell and the doped GaAsP back contact layer.

### Claim 10 (depends on 9)

The method of claim 9, including affixing a metal front contact grid on the doped GaAsP front contact layer, removing the doped GaAsP front contact layer from openings between portions of the metal front contact grids, applying a front anti-reflection coating on the passivation/window layer, mounting the metal front contact grid on a transparent handle, removing the parent substrate and the graded layer, affixing a metal back contact grid on the doped GaAsP back contact layer, removing the doped GaAsP back contact layer between portions of the metal back contact grid, and applying a back anti-reflection coating on the back surface confinement layer.

### Claim 11 (depends on 10)

The method of claim 10, wherein removing the parent substrate and the graded layer further comprises:
growing an etch-stop layer between graded layer and the GaAsP back contact layer;
removing the parent substrate and graded layer by etching them away with an etchant that is selective for the substrate and graded layer and does not react with the etch-stop layer; and then
removing the etch-stop layer.

### Claim 12 (depends on 11)

The method of claim 11, including growing the cell upright.

### Claim 13 (depends on 11)

The method of claim 11, including growing the cell inverted.

### Claim 14 (depends on 9)

The method of claim 9, including affixing a metal back contact grid on the doped GaAsP back contact layer, removing the doped GaAsP back contact layer from openings between portions of the back contact grid, applying a back anti-reflection coating on the back surface confinement layer, mounting the metal back contact grid metal back contact grid metal back contact grid on a transparent handle, and removing the parent substrate and graded layer.

### Claim 15 (depends on 14)

The method of claim 14, wherein removing the parent substrate and graded layer further comprises:
removing the parent substrate and graded layer by etching them away with an etchant that is selective for the parent substrate and graded layer and does not react with the etch-stop layer, and then removing the etch-stop layer.

### Claim 16 (depends on 15)

The method of claim 15, including growing the cell upright.

### Claim 17 (depends on 15)

The method of claim 15, including growing the cell inverted.

### Claim 18 (depends on 9)

The method of claim 9, including affixing a metal front contact grid on the doped GaAsP front contact layer, removing the doped GaAsP front contact layer from openings between portions of the metal front contact grid, applying a front anti-reflection coating on the passivation/window layer, mounting the on an interim handle, removing the parent substrate and the graded layer, affixing a metal back contact grid on the doped GaAsP back contact layer, removing the doped GaAsP back contact layer from opening between portions of the metal back contact grid, applying a back anti-reflection coating on the back surface confinement layer, mounting the metal back contact grid on a permanent transparent handle, and removing the interim handle.