Photovoltaic device and method of formation

1. A photovoltaic device comprising:

a semiconductor window layer;

a semiconductor absorber layer comprising CdTe adjacent the window layer, the semiconductor window layer and semiconductor absorber layer forming a p-n junction providing an electric field;

an interface layer adjacent to the semiconductor absorber layer comprising a mixture containing Cd, Zn and Te, wherein the interface layer has a first side directly on and facing the absorber layer and a second side; and

a contact layer directly on the second side of the interface layer.

2. The photovoltaic device of claim 1 , wherein the concentration of Zn in the interface layer increases in accordance with a distance away from the first side of the interface layer.

3. The photovoltaic device of claim 1 , wherein the mole ratio of the interface layer is Cd 1-x Zn x Te, where x defines a number between 0 and 1.

4. The photovoltaic device of claim 3 , wherein x defines a number greater than about 0.2.

5. The photovoltaic device of claim 3 , wherein x defines a number greater than about 0.5.

6. The photovoltaic device of claim 3 , wherein x defines a number less than about 0.8.

7. The photovoltaic device of claim 3 , wherein x defines a number less than about 0.5.

8. The photovoltaic device of claim 3 , wherein x defines a number from about 0.2 to 0.3.

9. The photovoltaic device of claim 3 , wherein x defines a number from about 0.6 to 0.8.

10. The photovoltaic device of claim 1 , wherein x defines a number between about 0.8 and 1.

11. The photovoltaic device of claim 3 , wherein x is equal to about 0 at the first side of the interface layer and about 1 at the second side of the interface layer.

12. The photovoltaic device of claim 1 , wherein the interface layer comprises a stack of discrete interface layers, each layer comprising a mixture containing Cd, Zn and Te and each layer having uniform mixture of Cd and Zn, and each layer having a different concentration of Cd and Zn.

13. The photovoltaic device of claim 12 , wherein the mole-to-mole ratio of Cd to Zn in each discrete interface layer decreases incrementally the further away the discrete interface layer is from the semiconductor absorber layer.

14. The photovoltaic device of claim 13 , wherein the mole-to-mole ratio of Cd to Zn in each discrete interface layer is about (1−x):x, where x defines a different number between 0 and 1 for each discrete interface layer.

15. The photovoltaic device of claim 11 , wherein the concentration of Cd and Zn changes continually from said first side of the interface layer to said second side.

16. The photovoltaic device of claim 1 , wherein the concentration of Zn in the interface layer is lower on the first side of the interface layer facing the semiconductor absorber layer and higher on the second side of the interface layer facing the contact layer.

17. The photovoltaic device of claim 1 , wherein the mole-to-mole ratio between Cd and Zn throughout the interface layer is about (1−x):x, where x defines a number from 0 to 1.

18. The photovoltaic device of claim 1 , wherein the mole-to-mole ratio between Cd and Zn throughout the interface layer is about (1−x):x, where x defines a number greater than about 0.2.

19. The photovoltaic device of claim 1 , wherein the mole-to-mole ratio between Cd and Zn throughout the interface layer is about (1−x):x, where x defines a number greater than about 0.5.

20. The photovoltaic device of claim 1 , wherein the mole-to-mole ratio between Cd and Zn throughout the interface layer is about (1−x):x, where x defines a number less than about 0.8.

21. The photovoltaic device of claim 1 , wherein the mole-to-mole ratio between Cd and Zn throughout the interface layer is about (1−x):x, where x defines a number less than about 0.5.

22. The photovoltaic device of claim 1 , wherein the mole-to-mole ratio between Cd and Zn throughout the interface layer is about (1−x):x, where x defines a number from about 0.2 to about 0.3.

23. The photovoltaic device of claim 1 , wherein the mole-to-mole ratio between Cd and Zn throughout the interface layer is about (1−x):x, where x defines a number from about 0.6 to 0.8.

24. The photovoltaic device of claim 1 , wherein the mole-to-mole ratio between Cd and Zn throughout the interface layer is about (1−x):x, where x defines a number from about 0.8 to 1.

25. The photovoltaic device of claim 17 , wherein x is equal to about 0 at the first side of the interface layer and about 1 at the second side of the interface layer.

26. The photovoltaic device of claim 16 , wherein the interface layer comprises a stack of discrete interface layers, each layer comprising a mixture containing Cd, Zn and Te and each layer having a uniform mixture of Cd and Zn, each layer having a different concentration of Cd and Zn.

27. The photovoltaic device of claim 26 , wherein the mole-to-mole ratio of Cd to Zn in each discrete interface layer decreases incrementally moving from the semiconductor absorber layer toward the third semiconductor material.

28. The photovoltaic device of claim 27 , wherein the mole-to-mole ratio of Cd and Zn in each discrete interface layer is about (1−x):x, where x defines a different number from 0 to 1 for each discrete interface layer.

29. A photovoltaic device comprising:

a substrate;

a semiconductor window layer;

a semiconductor absorbing layer comprising CdTe over the window layer, the absorber layer and window layer forming a p-n junction producing an electric field;

an intermediate semiconductor interface layer comprising a mixture of Cd and Zn over the semiconductor absorbing layer, wherein the intermediate semiconductor interface has a first side directly on and facing the semiconductor absorbing layer and a second side; and

a contact layer directly on the second side of the intermediate semiconductor interface layer, wherein the concentration of Cd relative to Zn is higher on the first side of the intermediate semiconductor interface layer facing the semiconductor absorbing layer and lower on the second side of the intermediate semiconductor interface layer.

30. The photovoltaic device of claim 26 , wherein the Cd and Zn composition of the intermediate semiconductor interface layer goes from being approximately 70% Cd and 30% Zn at the first side of the intermediate semiconductor interface layer to approximately 30% Cd and 70% Zn at the second side of the intermediate semiconductor interface layer.

31. The photovoltaic device of claim 29 , wherein the Cd and Zn composition of the intermediate semiconductor interface layer goes from being approximately 80% Cd and 20% Zn at the first side of the intermediate semiconductor layer to approximately 20% Cd and 80% Zn at the second side of the intermediate semiconductor interface layer.

32. The photovoltaic device of claim 29 , wherein the Cd and Zn composition of the intermediate semiconductor layer goes from being approximately 90% Cd and 10% Zn at the first side of the intermediate semiconductor interface layer to approximately 10% Cd and 90% Zn at the second side of the intermediate semiconductor interface layer.

33. The photovoltaic device of claim 29 , wherein the Cd and Zn composition of the intermediate semiconductor interface layer goes from being approximately 100% Cd and 0% Zn at the first side of the intermediate semiconductor interface layer Zn to approximately 0% Cd and 100% Zn at the second side of the intermediate semiconductor interface layer.

34. The photovoltaic device of claim 29 , wherein the intermediate semiconductor interface layer includes a plurality of layers of different compositions of Cd and Zn.

35. The photovoltaic device of claim 34 , wherein the plurality of layers of different compositions of Cd and Zn each comprise cadmium zinc telluride.

36. The photovoltaic device of claim 35 wherein the plurality of different layers of different compositions of Cd and Zn comprises:

a first layer having a Cd and Zn composition of greater than approximately 80% percent Cd and being closest to the semiconductor absorbing layer;

a second layer having a Cd and Zn composition of greater than approximately 80% Zn and being farthest from the semiconductor absorbing layer; and

at least a third layer between the first and second layers having a Cd and Zn composition of less than approximately 80% Cd and less than approximately 80% Zn.

37. The photovoltaic device of claim 29 further comprising a semiconductor reflecting layer comprising Zn between the intermediate semiconductor interface layer and the contact layer.

38. The photovoltaic device of claim 37 , wherein the Cd and Zn composition of the intermediate semiconductor interface layer goes from being approximately 70% Cd and 30% Zn at the first side of the intermediate semiconductor interface layer to approximately 30% Cd and 70% Zn at the second side of the intermediate semiconductor interface layer.

39. The photovoltaic device of claim 37 , wherein the Cd and Zn composition of the intermediate semiconductor interface layer goes from being approximately 80% Cd and 20% Zn at the first side of intermediate semiconductor interface layer to approximately 20% Cd and 80% Zn at the second side of the intermediate semiconductor interface layer.

40. The photovoltaic device of claim 37 , wherein the Cd and Zn composition of the intermediate semiconductor interface layer goes from being approximately 90% Cd and 10% Zn at the first side of the intermediate semiconductor interface layer to approximately 10% Cd and 90% Zn at the second side of the intermediate semiconductor interface layer.

41. The photovoltaic device of claim 37 , wherein the Cd and Zn composition of the intermediate semiconductor interface layer goes from being approximately 100% Cd and 0% Zn at the first side of the intermediate semiconductor interface layer to approximately 0% Cd and 100% Zn at the second side of the intermediate semiconductor interface layer.

42. The photovoltaic device of claim 37 , wherein the intermediate semiconductor interface layer includes a plurality of layers of different compositions.

43. The photovoltaic device of claim 42 , wherein the plurality of layers of different Cd and Zn compositions each comprise cadmium zinc telluride.

44. The photovoltaic device of claim 43 , wherein the plurality of layers of different Cd and Zn compositions comprises:

a first layer having a Cd and Zn composition of greater than approximately 80% percent Cd and being closest to the semiconductor absorbing layer;

a second layer having a Cd and Zn composition of greater than approximately 80% Zn and being closest to the semiconductor reflecting layer; and

at least a third layer between the first and second layers having a Cd and Zn composition of less than approximately 80% Cd and less than approximately 80% Zn.

45. A photovoltaic device comprising:

an absorber layer comprising CdTe, wherein the absorber layer and another layer form a p-n junction which produces an electric field;

a cadmium zinc telluride layer over the absorber layer, wherein the cadmium zinc telluride layer has a first side in contact with and facing the absorber layer and an opposite second side; and

a contact layer over and in contact with the opposite second side of the cadmium zinc telluride layer.

46. The photovoltaic device of claim 45 , wherein the concentration of cadmium relative to zinc in the cadmium zinc telluride layer is higher on the first side of the cadmium zinc telluride layer facing the absorber layer and lower on the opposite second side of the cadmium zinc telluride layer.

47. The photovoltaic device of claim 46 , wherein the decrease from the higher concentration of cadmium in the cadmium zinc telluride layer to the lower concentration of cadmium in the cadmium zinc telluride layer is gradual.

48. The photovoltaic device of claim 46 , wherein the decrease from the higher concentration of cadmium in the cadmium zinc telluride layer to the lower concentration of cadmium in the cadmium zinc telluride layer is stepped.