Photovoltaic device with three dimensional charge separation and collection

Patent metadata

Field	Value
Publication number	US-9660126-B2
Application number	US-201113312780-A
Country	US
Kind code	B2
Filing date	Dec 6, 2011
Priority date	Dec 6, 2010
Publication date	May 23, 2017
Grant date	May 23, 2017

Abstract

A photovoltaic device having three dimensional (3D) charge separation and collection, where charge separation occurs in 3D depletion regions formed between a p-type doped group III-nitride material in the photovoltaic device and intrinsic structural imperfections extending through the material. The p-type group III-nitride alloy is compositionally graded to straddle the Fermi level pinning by the intrinsic structural imperfections in the material at different locations in the group III-nitride alloy. A field close to the surfaces of the intrinsic defects separates photoexcited electron-hole pairs and drives the separated electrons to accumulate at the surfaces of the intrinsic defects. The intrinsic defects function as n-type conductors and transport the accumulated electrons to the material surface for collection. The compositional grading also creates a potential that drives the accumulated separated electrons toward an n-type group III-nitride layer for collection. The p-type group III-nitride alloy may comprise an alloy of InGaN, InAlN or InGaAlN.

First claim

What is claimed is:

1. A solar cell, comprising:
a layer of a p-type Group III-nitride alloy for absorbing a portion of the solar spectrum upon exposure to light to generate photoexcited electron-hole pairs, wherein the p-type Group III-nitride alloy includes a top surface and a bottom surface, wherein the p-type Group III-nitride alloy includes a conduction band having a conduction band edge and a valence band having a valence band edge having a band gap there between the conduction band edge and the valence band edge;
a plurality of structural imperfections within the p-type Group III-nitride alloy, each of the structural imperfections having a surface that extends over a full distance from a point on the top surface to a point on the bottom surface of the p-type Group III-nitride alloy, wherein a Fermi level stabilization energy, E FS , exists representing a Fermi level pinning position at the surfaces of the structural imperfections;
wherein the p-type Group III-nitride alloy is compositionally graded along the plurality of structural imperfections between at least a first area and a second area of the p-type Group III-nitride alloy such that the first area possesses a first composition of the p-type Group III-nitride alloy having its conduction band edge beneath the Fermi level stabilization energy, E FS , and the second area possesses a second composition of the p-type Group III-nitride alloy having its conduction band edge above the Fermi level stabilization energy, E FS ; and
a layer of n-type Group III-nitride alloy.

2. The solar cell of claim 1 , further comprising an electrostatic field between each of the plurality of structural imperfections and the p-type Group III-nitride alloy for separating the photoexcited electron-hole pairs and accumulating electrons around the structural imperfections in the first area possessing a first composition of the p-type Group III-nitride alloy having its conduction band edge beneath the Fermi level stabilization energy, E FS .

3. The solar cell of claim 2 , wherein the compositional grading of the p-type Group III-nitride alloy creates a potential that drives the electrons accumulating around the structural imperfections to the layer of n-type Group III-nitride alloy for collection.

4. The solar cell of claim 3 , wherein the charge separation of the photoexcited electron-hole pairs is performed separately from collection of the electrons at the n-type Group III-nitride alloy.

5. The solar cell of claim 2 , wherein the p-type Group III-nitride alloy layer comprises In x Ga 1-x N, where 0≦x≦1.0, wherein the first composition of the p-type Group III-nitride alloy having its conduction band edge beneath the Fermi level stabilization energy, E FS , comprises In x Ga 1-x N, where 0.35<x≦1.0 and wherein the second composition of the p-type Group III-nitride alloy having its conduction band edge above the Fermi level stabilization energy, E FS , comprises In x Ga 1-x N, where x<0.35.

6. The solar cell of claim 2 , wherein the p-type Group III-nitride alloy layer comprises In y Al 1-y N, where 0≦y≦1.0, wherein the first composition of the p-type Group III-nitride alloy having its conduction band edge beneath the Fermi level stabilization energy, E FS , comprises In y Al 1-y N where 0.57<y≦1.0 and wherein the second composition of the p-type Group III-nitride alloy having its conduction band edge above the Fermi level stabilization energy, E FS , comprises In y Al 1-y N where y<0.57.

7. The solar cell of claim 2 , wherein the p-type Group III-nitride alloy layer comprises an alloy of In x Al y Ga 1-x-y N, where 0≦x, y≦1.

8. The solar cell of claim 1 , wherein the structural imperfections comprise at least one of threading dislocations, grain boundaries, and/or columns in the p-type Group III-nitride alloy.

9. The solar cell of claim 2 , wherein the structural imperfections are n-type conductors in the first area possessing a first composition of the p-type Group III-nitride alloy having its conduction band edge beneath the Fermi level stabilization energy, E FS , to transport the accumulated photoexcited electrons to the layer of n-type Group III-nitride alloy.

10. The solar cell of claim 1 , further comprising:
a first electrical contact coupled to the p-type Group III-nitride alloy layer;
a silicon base substrate; and
a second electrical contact coupled to the silicon base substrate.

11. The solar cell of claim 10 , further comprising at least one buffer layer formed between the silicon base substrate and the n-type Group III-nitride alloy layer.

12. The solar cell of claim 10 , wherein the p-type Group III-nitride alloy layer and the n-type Group III-nitride alloy layer form a top cell in the solar cell for absorbing a first portion of the solar spectrum, wherein the silicon base substrate is formed to possess a p-type region and an n-type region so as to form a bottom p-n junction cell in the solar cell for absorbing a second portion of the solar spectrum.

13. A solar cell, comprising:
a layer of a p-type Group III-nitride alloy for absorbing a portion of the solar spectrum upon exposure to light to generate photoexcited electron-hole pairs, wherein the p-type Group III-nitride alloy includes a top surface and a bottom surface;
a plurality of structural imperfections within the p-type Group III-nitride alloy, each of the structural imperfections having a surface that extends a full distance from the top surface to the bottom surface of the p-type Group III-nitride alloy;
wherein the p-type Group III-nitride alloy is compositionally graded along the plurality of structural imperfections between at least a first area and a second area of the p-type Group III-nitride alloy such that the first area possesses a first composition of the p-type Group III-nitride alloy having a conduction band edge beneath a Fermi level stabilization energy, and the second area possesses a second composition of the p-type Group III-nitride alloy having a conduction band edge above the Fermi level stabilization energy; and
a layer of n-type Group III-nitride alloy underlying the layer of p-type Group III-nitride alloy.

14. The solar cell of claim 13 , further comprising a silicon substrate underlying the layer of n-type Group III-nitride alloy.

15. The solar cell of claim 13 , wherein the p-type Group III-nitride alloy layer comprises In x Ga 1-x N, where 0≦x≦1.0, wherein the first composition of the p-type Group III-nitride alloy comprises In x Ga 1-x N, where 0.35<x≦1.0 and wherein the second composition of the p-type Group III-nitride alloy comprises In x Ga 1-x N, where x<0.35.

16. The solar cell of claim 13 , wherein the plurality of structural imperfections comprises a threading dislocation, and an electron accumulation area of the threading dislocation increases in size as the threading dislocation approaches the bottom surface of the p-type Group III-nitride alloy.

17. The solar cell of claim 13 , wherein the p-type Group III-nitride alloy layer comprises In y Al 1-y N, where 0≦y≦1.0, wherein the first composition of the p-type Group III-nitride alloy comprises In y Al 1-y N where 0.57<y≦1.0 and wherein the second composition of the p-type Group III-nitride alloy comprises In y Al 1-y N where y<0.57.

18. The solar cell of claim 13 , wherein the p-type Group III-nitride alloy layer comprises an alloy of In x Al y Ga 1-x-y N, where 0≦x, y≦1.

19. The solar cell of claim 13 , wherein the p-type Group III-nitride alloy layer has a thickness of at least 200 nm.

20. A solar cell, comprising:
a layer of

Assignees

• Walukiewicz Wladyslaw
• Reichertz Lothar A
• Gherasoiu Iulian
• Univ California

Inventors

• Walukiewicz Wladyslaw
• Reichertz Lothar A
• Gherasoiu Iulian

Classifications

• H01L31/03048

  Electricity · mapped topic

• Y02E10/544

  Solar cells from Group III-V materials · CPC title

• H01L31/065 Primary

  Electricity · mapped topic

• Y02P70/521

  Cross-Sectional Technologies · mapped topic

• H01L31/072

  Electricity · mapped topic