Method of making photovoltaic device comprising an absorber having a surface layer

1. A method of forming a photovoltaic device, comprising

forming an absorber layer above a substrate, the absorber layer comprising a I-III-VI 2 compound comprising a Group I element, a Group III element and a Group VI element; and

forming a surface layer on the absorber layer, the surface layer comprising a I-III-VI 2 compound comprising a Group I element, a Group III element and a Group VI element, and having an atomic ratio of the Group I element to the Group III element in the range of from 0.1 to 0.9.

2. The method of claim 1 , wherein

the Group I element in the I-III-VI 2 compound in the absorber layer or in the I-III-VI 2 compound in the surface layer is selected from a group consisting of Cu and Ag.

3. The method of claim 1 , wherein

the Group III element in the I-III-VI 2 compound in the absorber layer or in the I-III-VI 2 compound in the surface layer is selected from a group consisting of Al, Ga, In and Tl.

4. The method of claim 1 , wherein

The Group VI element in the I-III-VI 2 compound in the absorber layer or in the I-III-VI 2 compound in the surface layer is selected from a group consisting of S and Se.

5. The method of claim 1 , wherein

the atomic ratio of the Group I element to the Group III element in the I-III-VI 2 compound in the surface layer is in the range of from 0.1 to 0.7.

6. The method of claim 1 , wherein

the atomic ratio of the Group I element to the Group III element in the I-III-VI 2 compound in the surface layer is in the range of from 0.5 to 0.7.

7. The method of claim 1 , wherein the step of forming an absorber layer comprises

forming a metal precursor layer above a substrate, the metal precursor comprising a material selected from the group consisting of a Group I element, a Group III element, an alloy or any combination thereof;

depositing a selenium-containing precursor onto the metal precursor layer at a temperature in the range of from 200° C. to 800° C.;

annealing the photovoltaic device in an inert gas at a temperature in the range of from 200° C. to 800° C.; and

depositing a sulfur-containing precursor onto the metal precursor layer at a temperature in the range of from 200° C. to 600° C. after the step of annealing the photovoltaic device.

8. The method of claim 1 , wherein the step of forming an absorber layer comprises

forming a metal precursor layer above a substrate;

depositing a sulfur-containing precursor onto the metal precursor layer at a temperature in the range of from 300° C. to 550° C.;

depositing a selenium-containing precursor onto the metal precursor layer after the step of depositing a sulfur-containing precursor; and

annealing the photovoltaic device at a temperature in the range of from 500° C. to 800° C.

9. The method of claim 8 , wherein the step of depositing a selenium-containing precursor onto the metal precursor layer comprises:

depositing a selenium-containing precursor at a temperature in the range of from 25° C. to 350° C.; and

depositing a selenium-containing precursor at a temperature in the range of from 400° C. to 600° C.

10. The method of claim 1 , wherein the step of forming a surface layer on the absorber layer comprises

depositing a selenium-containing precursor at a temperature in the range of from 200° C. to 520° C.; and

depositing a sulfur-containing precursor onto the selenium-containing precursor at a temperature in the range of from 200° C. to 520° C.

11. The method of claim 10 , wherein the step of forming a surface layer on the absorber layer further comprises

depositing a metal precursor comprising a Group III element above the absorber layer before or when the selenium-containing precursor is deposited at a temperature in the range of from 200° C. to 520° C.

12. A method of fabricating a photovoltaic device according to claim 1 , further comprising

forming a back contact layer above the substrate;

wherein the step of forming a surface layer comprises:

depositing a selenium-containing precursor at a temperature in the range of from 25° C. to 520° C.; and

depositing a sulfur-containing precursor at a temperature in the range of from 200° C. to 520° C.

13. A method of claim 12 , wherein the step of forming a surface layer on the absorber layer further comprises

depositing a metal precursor comprising a Group III element above the absorber layer before or when the selenium-containing precursor is deposited at a temperature in the range of from 200° C. to 520° C.

14. The method of claim 12 , wherein in the step of forming a surface layer on the absorber layer, the selenium-containing precursor is deposited at a temperature lower than the temperature at which the sulfur-containing precursor is deposited.

15. The method of claim 12 , wherein in the step of forming a surface layer on the absorber layer, the selenium-containing precursor is deposited at a temperature in the range of from 300° C. to 400° C., and the sulfur-containing precursor is deposited at a temperature in the range of from 400° C. to 500° C.