Technique for achieving large-grain Ag

1. A method for forming an absorber film on a substrate, comprising:

contacting the substrate with an Ag source, a Zn source, a Sn source, and at least one of an S source and an Se source under conditions sufficient to form the absorber film on the substrate having a target composition of: Ag X Zn Y Sn(S,Se) Z , wherein 1.7<x<2.2, 0.9<y<1.3, and 3.5<z<4.5, and including an amount of the Ag source that is from about 10% to about 30% greater than is needed to achieve the target composition;

annealing the absorber film; and

removing excess Ag, if any, from the absorber film, wherein the excess Ag forms a secondary phase, and wherein the removing is performed after the annealing to remove the secondary phase from grain boundaries of the absorber film.

2. The method of claim 1 , wherein the conditions comprise a temperature, a duration, and a pressure.

3. The method of claim 2 , wherein the temperature is from about 10° C. to about 450° C.

4. The method of claim 2 , wherein the duration is from about 1 minute to about 200 minutes.

5. The method of claim 2 , wherein the pressure is from about 1×10 −5 Torr to about 5×10 −10 Torr.

6. The method of claim 1 , wherein the annealing is performed at a temperature of from about 430° C. to about 550° C.

7. The method of claim 1 , wherein the annealing is performed for a duration of from about 20 seconds to about 10 minutes.

8. The method of claim 1 , wherein the secondary phase is selected from the group consisting of: Ag 2 Se, Ag 6 SnSe 8 , and combinations thereof.

9. The method of claim 1 , wherein the excess Ag is removed using an etchant selected from the group consisting of: potassium cyanide, sodium cyanide, and combinations thereof.

10. The method of claim 1 , wherein the absorber film has an average grain size of from about 0.5 micrometers to about 4 micrometers.

11. The method of claim 1 , further comprising:

measuring composition of the absorber film using Particle Induced X-ray Emission (PIXE) techniques.

12. A method of forming a solar cell, comprising:

contacting a conducting substrate with an Ag source, a Zn source, a Sn source, and at least one of an S source and an Se source under conditions sufficient to form the absorber film on the conducting substrate having a target composition of: Ag X Zn Y Sn(S,Se) Z , wherein 1.7<x<2.2, 0.9<y<1.3, and 3.5<z<4.5, and including an amount of the Ag source that is from about 10% to about 30% greater than is needed to achieve the target composition;

annealing the absorber film;

removing excess Ag, if any, from the absorber film, wherein the excess Ag forms a secondary phase, and wherein the removing is performed after the annealing to remove the secondary phase from grain boundaries of the absorber film;

forming a buffer layer on the absorber layer; and

forming a transparent front contact on the buffer layer.

13. The method of claim 12 , wherein the conditions comprise a temperature of from about 10° C. to about 450° C., a duration of from about 1 minute to about 200, and a pressure of from about 1×10 −5 Torr to about 5×10 −10 Torr.

14. The method of claim 12 , wherein the annealing is performed at a temperature of from about 430° C. to about 550° C., for a duration of from about 20 seconds to about 10 minutes.

15. The method of claim 12 , wherein the secondary phase is selected from the group consisting of: Ag 2 Se, Ag 6 SnSe 8 , and combinations thereof.

16. The method of claim 12 , wherein the excess Ag is removed using an etchant selected from the group consisting of: potassium cyanide, sodium cyanide, and combinations thereof.

17. The method of claim 12 , wherein the absorber film has an average grain size of from about 0.5 micrometers to about 4 micrometers.