Bandgap grading of CZTS solar cell

Patent metadata

Field	Value
Publication number	US-10978604-B2
Application number	US-201715592669-A
Country	US
Kind code	B2
Filing date	May 11, 2017
Priority date	Sep 14, 2015
Publication date	Apr 13, 2021
Grant date	Apr 13, 2021

Abstract

A method for fabricating a photovoltaic device includes forming a polycrystalline absorber layer including Cu—Zn—Sn—S(Se) (CZTSSe) over a substrate. The absorber layer is rapid thermal annealed in a sealed chamber having elemental sulfur within the chamber. A sulfur content profile is graded in the absorber layer in accordance with a size of the elemental sulfur and an anneal temperature to provide a graduated bandgap profile for the absorber layer. Additional layers are formed on the absorber layer to complete the photovoltaic device.

First claim

The invention claimed is:

1. A photovoltaic device, comprising:
a first contact layer on a substrate;
a polycrystalline absorber layer including Cu—Zn—Sn—S(Se) (CZTSSe) on the first contact layer, wherein the polycrystalline absorber layer has a front surface region of about 100 nm in thickness from a front surface of the absorber layer farthest from the first contact layer, and the polycrystalline absorber layer further has a graded bandgap across its thickness that includes an exponential gradation in the front surface region provided by a S/Se ratio of about 1.2 to about 11 in the front surface region;
a buffer layer in physical contact with the absorber layer, wherein the concentration of sulfur in the polycrystalline absorber layer is greatest at a junction with the buffer layer and decreases towards the interior of the absorber layer, thereby forming a graded sulfur content profile; and
a transparent conductive contact layer formed over the buffer layer formed on the polycrystalline absorber layer.

2. The device as recited in claim 1 , wherein the concentration of sulfur in the absorber layer is higher at the junction with the buffer layer and at a junction with the first contact layer than in the interior of the absorber layer.

3. The device as recited in claim 1 , wherein the S/Se ratio increases about 5 to about 10 times in the front surface region.

4. The device as recited in claim 1 , wherein the absorber layer includes a polycrystalline structure with grains larger than 500 nm.

5. The device as recited in claim 1 , wherein the graded bandgap transition transitions to a substantially constant bandgap outside of the front surface region.

6. A photovoltaic device, comprising:
an absorber layer including Cu—Zn—Sn—S(Se) (CZTSSe) formed on a first contact layer on a substrate, wherein the absorber layer includes a graded bandgap across its thickness, a front surface region of about 100 nm in thickness from a front surface of the absorber layer farthest from the first contact layer, that includes an exponential gradation in the front surface region; and
a buffer layer in physical contact with the absorber layer that forms an interface, wherein the ratio of sulfur to selenium (S/Se) at the interface with the buffer layer is in a range of about 2 times to about 10 times greater than the ratio of sulfur to selenium (S/Se) at a distance of about 0.25 microns from the interface.

7. The photovoltaic device of claim 6 , wherein the absorber layer has a thickness of about 2 microns.

8. The photovoltaic device of claim 6 , wherein the buffer layer is Cu—In—Ga—S,Se (CIGSSe).

9. The photovoltaic device of claim 6 , wherein the absorber layer is poly crystalline having a grain size of greater than about 500 nm.

Assignees

• IBM

Inventors

• Gershon Talia S
• Hopstaken Marinus J P
• Kim Jeehwan
• Lee Yun Seog

Classifications

• H10F77/244

  made of transparent conductive layers, e.g. transparent conductive oxide [TCO] layers · CPC title

• H10F77/164

  Polycrystalline semiconductors · CPC title

• H10F77/128 Primary

  comprising only Group I-II-IV-VI kesterite materials, e.g. Cu2ZnSnSe4 or Cu2ZnSnS4 · CPC title

• H10F71/138

  Manufacture of transparent electrodes, e.g. transparent conductive oxides [TCO] or indium tin oxide [ITO] electrodes · CPC title

• H10F71/128

  Annealing · CPC title