Methods for forming thin-film heterojunction solar cells from I-III-VI.sub. 2

• US RE31,968 E
• Filed: 06/14/1984
• Issued: 08/13/1985
• Est. Priority Date: 12/31/1980
• Status: Expired due to Term

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Chen, Wen S., Mickelsen, Reid A.
• Primary Examiner(s): Weisstuch, Aaron
• Application Number:
  US06/620,637
• Time in Patent Office: 425 Days
• Field of Search: 136/252, 136/255, 136/258 PC, 136/260, 136/264, 136/265, 427/74, 427/76, 427/87, 427/255.2, 148/174, 148/178, 357/16, 357/30, 29/572
• US Class Current: 136/260
• CPC Class Codes: H01L 31/0322 comprising only AIBIIICVI chalcopyrite compounds, e.g. Cu In Se2, Cu Ga Se2, Cu In Ga Se2
• CPC Class Codes: H01L 31/03365 comprising only Cu2X / CdX heterojunctions, X being an element of Group VI of the Periodic Table
• CPC Class Codes: H01L 31/072 the potential barriers being only of the PN heterojunction type
• CPC Class Codes: H01L 31/0749 including a AIBIIICVI compound, e.g. CdS/CulnSe2 [CIS] heterojunction solar cells
• CPC Class Codes: H01L 31/18 Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
• CPC Class Codes: Y02E 10/541 CuInSe2 material PV cells

Abstract

An improved thin-film, large area solar cell, and methods for forming the same, having a relatively high light-to-electrical energy conversion efficiency and characterized in that the cell comprises a p-n type heterojunction formed of: (i) a first semiconductor layer comprising a photovoltaic active material selected from the class of I-III-VI₂ chalcopyrite ternary materials which is vacuum deposited in a thin "composition-graded" layer ranging from on the order ot about 2.5 microns to about 5.0 microns (≅2.5 μm to ≅5.0 μm) and wherein the lower region of the photovoltaic active material preferably comprises a low resistivity region of p-type semiconductor material having a superimposed region of relatively high resistivity, transient n-type semiconductor material defining a transient p-n homojunction; and (ii), a second semiconductor layer comprising a low resistivity n-type semiconductor material; wherein interdiffusion (a) between the elemental constituents of the two discrete juxtaposed regions of the first semiconductor layer defining a transient p-n homojunction layer, and (b) between the transient n-type material in the first semiconductor layer and the second n-type semiconductor layer, causes the

The Government has rights in this invention pursuant to Contract No. EG-77-C-01-4042, Subcontract No. XJ-9-8021-1 awarded by the U.S. Department of Energy.

Claims

1. In a method of forming a photovoltaic light-to-electrical energy transducer of the type including a thin-film A-B-type heterojunction where "A" and "B" are selected from the group of semiconductor materials consisting of:

space="preserve" listing-type="tabular">______________________________________ A and B ______________________________________ (i) a p-type ternary material and an n-type material;

(ii) an n-type ternary material and a p-type material;

(iii) an n-type material and a p-type ternary material;

(iv) a p-type material and an n-type ternary material;

______________________________________

and wherein the transducer includes a substrate, a first contact deposited on the substrate, a first semiconductor layer formed of A-type material deposited on the first contact, a second semiconductor layer formed of B-type material deposited on the first semiconductor layer and defining therewith the thin-film A-B-type heterojunction, and a second contact deposited on the second semiconductor layer, the improvement comprising a method wherein;

(a) the one of the first and second semiconductor layers formed of a ternary semiconductor material is formed by simultaneous elemental evaporation of the ternary semiconductor material to form a semiconductor layer having two composition graded regions sequentially formed one upon the other with one region having a first preselected ratio of two of the elements in the ternary semiconductor material so as to form a low resistivity semiconductor region and the other of the regions having a different preselected ratio of the same two elements so as to form a high resistivity transient semiconduction region and with the two regions defining a transient homojunction; and

(b) the other of the first and second semiconductor layers is formed by deposition of a semiconductor material in face-to-face contact with respect to the high resistivity transient semiconductor region of the transient homojunction so as to permit the high resistivity transient semiconductor region to evolve through elemental interdiffusion into a region of relatively high resistivity semiconductor material of the same type as the low resistivity region formed in step (a) to thereby form a thin-film A-B type heterojunction photovoltaic light-to-electrical energy transducer.

2. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claim 1 wherein the A-B-type heterojunction is a p-n-type heterojunction and the one semiconductor layer defining the transient homojunction defines a transient p-n-type homojunction having a region of low resistivity p-type material and a region of high resistivity transient n-type material, and the other semiconductor layer is formed of n-type semiconductor material deposited in face-to-face contact with the region of high resistivity transient n-type material.

3. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claim 1 wherein the A-B-type heterojunction is an n-p-type heterojunction and the one semiconductor layer defining the transient homojunction defines a transient n-p type homojunction having a region of high resistivity transient n-type material and a region of low resistivity p-type material, and the other semiconductor layer is formed of n-type semiconductor material deposited in face-to-face contact with the region of high resistivity transient n-type material.

4. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claim 1 wherein the ternary material is selected from the group of I-III-VI₂ chalcopyrite compounds.

5. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claim 1 wherein the ternary material is selected from the group of I-III-VI₂ chalcopyrite compounds and the other of the first and second semiconductor layers is formed of materials selected from the group of II-VI elements.

6. The method of forming a photovoltaic light-to electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 4 or 5 wherein the ternary material has a band gap energy in the range of 1-1.5 ev.

7. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 4 or 5 wherein the ternary material has a band gap energy in the range of 1-1.5 ev and the other of the first and second semiconductor layers is formed of materials having a band gap energy greater than 1.5 ev.

8. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 1, 2 or 3 wherein the ternary semiconductor material is CuInSe₂.

9. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 1, 2 or 3 wherein the other of the first and second semiconductor layers has a band gap energy greater than 1.5 ev.

10. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 1, 2 or 3 wherein the other of the first and second semiconductor layers is selected from the group consisting of

CdS;

Cd_1-x Zn_x S; and

,

CdS_1-x Se_x.

11. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 1, 2 or 3 wherein the ternary semiconductor material is CuInSe₂ and the other of the first and second semiconductor layers is selected from the group consisting of:

CdS;

Cd_1-x Zn_x S; and

,

CdS_1-x Se_x.

12. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 1, 2, or 3 wherein the ternary semiconductor material is CuInSe₂ and the other of the first and second semiconductor layers is CdS.

13. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 1, 2 or 3 wherein the ternary semiconductor material is a I-III-VI₂ chalcopyrite compound and the ratio of the I-III elements is adjusted during one portion only of simultaneous elemental evaporation of the ternary compound so as to form one of the low resistivity and transient high resistivity regions of the transient homojunction, and adjusted to a different I-III ratio during the remaining portion of simultaneous elemental evaporation of the ternary compound so as to form the other of the low resistivity and the transient high resistivity regions of the transient homojunction.

14. The method of forming a photovoltaic light-to-electrical energy transducer including the thin-film A-B-type heterojunction as set forth in claims 1 or 2 wherein the ternary semiconductor layer is CuInSe₂ and the copper/indium ratio is initially adjusted to form a slightly copper-enriched region during simultaneous elemental evaporation of the CuInSe₂ to form the low resistivity region of the transducer of p-type material, and is readjusted to form a slightly copper-deficient region during simultaneous elemental evaporation of the CuInSe₂ to form the high resistivity transient semiconductor region of the transducer of transient n-type material.

15. The product produced by the method set forth in claims 1, 2, 3, 4 or 5.

16. In a photovoltaic light-to-electrical energy transducer of the type including a thin-film A-B-type heterojunction where "A" and "B" are selected from the group of semiconductor materials consisting of:

space="preserve" listing-type="tabular">______________________________________ A and B ______________________________________ (i) a p-type ternary material and an n-type material;

(ii) an n-type ternary material and a p-type material;

(iii) an n-type material and a p-type ternary material;

(iv) a p-type material and an n-type ternary material;

______________________________________

and wherein the transducer includes a substrate, a first contact deposited on said substrate, a first semiconductor layer formed of A-type material deposited on said first contact, a second semiconductor layer formed of B-type material deposited on said first semiconductor layer and defining therewith the thin-film A-B-type heterojunction, and a second contact deposited on said second semiconductor layer, the improvement comprising;

(a) the one of said first and second semiconductor layers formed of a ternary semiconductor material comprising a semiconductor layer having been formed with two composition graded regions with one region superimposed on the other and with one region having a first preselected ratio of two of the elements in said ternary semiconductor material so as to form a low resistivity semiconductor region and the other of said regions having a different preselected ratio of the same two elements and having been formed as a high resistivity transient semiconductor region and with said two regions having been formed as a transient homojunction; and

,

(b) the other of said first and second semiconductor layers having been formed in face-to-face contact with said high resistivity transient semiconductor region of said transient homojunction so as to permit said high resistivity transient semiconductor region to evolve through elemental interdiffusion into a region of relatively high resistivity semiconductor material of the same type as said low resistivity region to thereby form a thin-film A-B-type heterojunction photovoltaic light-to-electrical energy transducer.

17. The photovoltaic light-to-electrical energy transducer set forth in claim 16 and including a thin-film A-B-type heterojunction wherein said A-B-type heterojunction is a p-n-type heterojunction and said one semiconductor layer defining said transient homojunction having been formed as a transient p-n-type homojunction having a region of low resistivity p-type material and a region of high resistivity transient n-type material, and said other semiconductor layer is formed of n-type semiconductor material deposited in face-to-face contact with said region of high resistivity transient n-type material.

18. The photovoltaic light-to-electrical energy transducer set forth in claim 16 and including a thin-film A-B-type heterojunction wherein said A-B-type heterojunction is an n-p-type heterojunction and said one semiconductor layer defining said transient homojunction having been formed as a transient n-p type homojunction having a region of high resistivity transient n-type material and a region of low resistivity p-type material, and said other semiconductor layer is formed of n-type semiconductor material deposited in face-to-face contact with said region of high resistivity transient n-type material.

19. The photovoltaic light-to-electrical energy transducer as set forth in claim 16 and including a thin-film A-B-type heterojunction wherein said ternary material is selected from the group of I-III-VI₂ chalcopyrite compounds.

20. The photovoltaic light-to-electrical energy transducer as set forth in claim 16 and including a thin-film A-B-type heterojunction wherein said ternary material is selected from the group of I-III-VI₂ chalcopyrite compounds and said other of said first and second semiconductor layers is formed of materials selected from the group of II-VI elements.

21. The photovoltaic light-to-electrical energy transducer as set forth in claims 19 or 20 and including a thin-film A-B-type heterojunction wherein said ternary material has a band gap energy in the range of 1-1.5 ev.

22. The photovoltaic light-to-electrical energy transducer as set forth in claims 19 or 20 and including a thin film A-B-type heterojunction wherein said ternary material has a band gap energy in the range of 1-1.5 ev and said other of said first and second semiconductor layers is formed of materials having a band gap energy greater than 1.5 ev.

23. The photovoltaic light-to-electrical energy transducer as set forth in claims 16, 17 or 18 and including a thin-film A-B-type heterojunction wherein said ternary semiconductor material is CuInSe₂.

24. The photovoltaic light-to-electrical energy transducer as set forth in claims 16, 17 or 18 and including a thin-film A-B-type heterojunction wherein said other of said first and second semiconductor layers has a band gap energy greater than 1.5 ev.

25. The photovoltaic light-to-electrical energy transducer as set forth in claims 16, 17 or 18 and including a thin-film A-B-type heterojunction wherein said other of said first and second semiconductor layers is selected from the group consisting of:

CdS;

Cd_1-x Zn_x S; and

,

CdS_1-x Se_x.

26. The photovoltaic light-to-electrical energy transducer as set forth in claims 16, 17 or 18 and including a thin-film A-B-type heterojunction wherein said ternary semiconductor material is CuInSe₂ and said other of said first and second semiconductor layers is selected from the group consisting of:

CdS;

Cd_1--x Zn_x S; and

,

CdS_1--x Se_x.

27. The photovoltaic light-to-electrical energy transducer as set forth in claims 16, 17 or 18 and including a thin-film A-B-type heterojunction wherein said ternary semiconductor material is CuInSe₂ and said other of said first and second semiconductor layers in CdS.

28. The method of forming a p-n-type heterojunction photovoltaic device comprising the steps of:

(a) depositing a first region of relatively low resistivity p-type material on a metallized substrate;

(b) depositing a second region of relatively high resistivity transient n-type material formed of the same elemental constituents as the relatively low resistivity p-type material deposited in step (a) with such transient n-type material being deposited on the first region of p-type material and defining therewith a transient p-n-type homojunction; and

,

(c) depositing a film of low resistivity n-type semiconductor material on the transient p-n-type homojunction formed in steps (a) and (b), whereupon interdiffusion of the constituent elements of the materials employed in steps (a), (b) and (c) between the p-type matrial and the transient n-type material, and between the transient n-type material and the n-type semiconductor material, causes the transient n-type material to evolve into relatively high resistivity p-type material so as to form a thin-film heterojunction essentially devoid of growth nodules and permitting a photovoltaic response characteristic of energy transducers capable of exhibiting relatively high conversion efficiencies at least approximating 10.0%.

29. The method of claim 28 wherein the first and second regions of p-type and transient n-type material, respectively, comprise a ternary semiconductor material formed by simultaneous elemental evaporation.

30. The method of claim 29 wherein the ternary semiconductor material is a chalcopyrite compound.

31. The method of claim 29 wherein the ternary semiconductor material is a material selected from the class of I-III-VI₂ chalcopyrite compounds.

32. The method of claim 29 wherein the ternary semiconductor material is CuInSe₂.

33. The method of claim 32 wherein the copper/indium ratio in the ternary semiconductor material is initially adjusted to form a slightly copper-enriched region during simultaneous elemental evaporation thereof to form the first region of relatively low resistivity p-type material in step (a) and is readjusted during such simultaneous elemental evaporation to form a slightly copper-deficient ternary compound during evaporation of the second region of relatively high resistivity transient n-type material formed in step (b).

34. The method of claim 32 wherein the copper/indium ratio is altered upon formation of at least about 50% of the total desired thickness of the transient p-n-type homojunction but prior to formation of about 66.7% of the total desired thickness of the transient p-n-type homojunction.

35. The method of claim 32 wherein the film of low resistivity n-type semiconductor material is formed of n-type material having a band gap energy greater than 1.5 ev.

36. The method of claim 35 wherein the n-type low resistivity semiconductor material is a II-VI material.

37. The method of claim 36 wherein the II-VI material is selected from the group consisting of:

CdS;

Cd_1--x Zn_x S; and

,

CdS_1--x Se_x.

38. The method of claim 36 wherein the II-VI material is CdS.

39. The method of claim 28 wherein the film of low-resistivity n-type semiconductor material comprises a first region of relatively pure CdS and a second superimposed region of indium-doped CdS.

40. The method of claim 28 wherein the first and second regions of semiconductor material formed in steps (a) and (b) are formed at a temperature in the range of 350°

C. to 500°

C.

41. The method of claim 28 wherein the first region of semiconductor material formed in step (a) and a portion of the second region of semiconductor material formed in step (b) are formed at a temperature in the range of 350°

C. to a temperature less than 450°

C., and the remainder of the second region of semiconductor material formed in step (b) is formed at a temperature in the range of about 450°

to 500°

C.

42. The method of claim 28 wherein the first region of semiconductor material formed in step (a) and a portion of the second region of semiconductor material formed in step (b) are formed at a temperature on the order of 350°

C., and the remainder of the second region of semiconductor material formed in step (b) is formed at a temperature on the order of 450°

C.±

approximately 25°

C.

43. The method of claim 28 wherein the film of low resistivity n-type semiconductor material formed in step (c) is formed at a temperature in the range of 150°

C. to 200°

C.

44. The method of claims 40, 41 or 42 wherein the film of low resistivity n-type semiconductor material formed in step (c) is formed at a temperature in the range of 150°

C. to 200°

C.

45. The method of claims 28, 30, 31, 32, 40, 41 or 42 wherein the first and second regions of semiconductor material formed in steps (a) and (b) are formed in an atmosphere maintained at 3-8×

10^-6 torr.

46. The method of claims 28, 29, 30, 31 or 32 wherein a grid-like contact is formed on the film of low resistivity n-type semiconductor material deposited in step (c) and an antireflective coating is formed on the grid-like contact and the exposed surface of the film of low resistivity n-type semiconductor material.

47. The method of claims 28, 29, 30, 31 or 32 wherein a grid-like contact is formed on the film of low resistivity n-type semiconductor material deposited in step (c) and an antireflectivecoating formed of SiO_x is formed on the grid-like contact and the exposed surface of the film of low resistivity n-type semiconductor material.

48. The method of claims 28, 29, 30, 31 or 32 wherein a grid-like contact is formed on the film of low resistivity n-type semiconductor material deposited in step (c) and an antireflective coating formed of SiO_x wherein "x" is on the order of "1.8" is formed on the grid-like contact and the exposed surface of the film of low resistivity n-type semiconductor material.

49. The product produced by the method set forth in claims 28, 29, 30, 31, 32, 40, 41, 42 or 43.

50. In a method of forming a photovoltaic light-to-electrical energy transducer of the type comprising a thin-film p-n-type heterojunction including a metallized substrate, a first semiconductor layer formed of p-type semiconductor material and deposited on the metallized substrate, a second semiconductor layer formed of low resistivity n-type semiconductor material formed on the first semiconductor layer, and a grid-like upper contact formed on the second semiconductor layer, the improvement comprising a method wherein:

(a) the first semiconductor layer of a ternary semiconductor material is formed by simultaneous elemental evaporation to form a first region of low resistivity p-type semiconductor material on the metallized substrate; and

,

(b) while the ternary material is undergoing simultaneous elemental evaporation the ratio of two of the elemental constituents being evaporated is adjusted so as to form a second region of relatively high resistivity transient n-type semiconductor material on the first region of low resistivity p-type material, thereby forming a transient p-n-type homojunction on the metallized substrate; and

, wherein upon formation of the second semiconductor layer of n-type material on the transient p-n homojunction, the second region of relatively high resistivity transient n-type semiconductor material is sandwiched between the first region of low resistivity p-type material and the second semiconductor layer of low resistivity n-type material so as to permit the transient n-type region to evolve through elemental interdiffusion into a region of relatively high resistivity p-type material to thereby form a thin-film p-n-type heterojunction photovoltaic light-to electrical energy transducer.

51. The method of claim 50 wherein the first and second regions of p-type and transient n-type material are formed by simultaneous elemental evaporation of a ternary semiconductor material.

52. The method of claim 51 wherein the ternary semiconductor material is a chalcopyrite compound.

53. The method of claim 51 wherein the ternary semiconductor material is a material selected from the class of I-III-VI₂ chalcopyrite compounds.

54. The method of claim 51 wherein the ternary semiconductor material is CuInSe₂.

55. The method of claim 54 wherein the copper/indium ratio in the ternary semiconductor material is initially adjusted to form a slightly copper-enriched region during simultaneous elemental evaporation thereof to form the first region of relatively low resistivity p-type material in step (a) and is readjusted during such simultaneous elemental evaporation to form a slightly copper-deficient ternary compound during evaporation of the second region of relatively high resistivity transient n-type material formed in step (b).

56. The method of claim 54 wherein the copper/indium ratio is readjusted upon formation of at least about 50% of the total desired thickness of the transient p-n-type homojunction but prior to formation of about 66.7% of the total desired thickness of the transient p-n-type homojunction.

57. The method of claim 54 wherein the second semiconductor layer of low resistivity n-type semiconductor material in CdS.

58. The method of claim 57 wherein the layer of low-resistivity n-type semiconductor material comprises a first region of relatively pure CdS and a second superimposed region of indium-doped CdS.

59. The method of claim 57 wherein the first and second regions of semiconductor material formed in steps (a) and (b) are formed at a temperature in the range of 350°

C. to 500°

C.

60. The method of claim 57 wherein the first region of semiconductor material formed in step (a) and a portion of the second region of semiconductor material formed in step (b) are formed at a temperature in the range of 350°

C. to a temperature less than 450°

C., and the remainder of the second region of semiconductor material formed in step (b) is formed at a temperature in the range of about 450°

to 500°

C.

61. The method of claim 57 wherein the first region of semiconductor material formed in step (a) and a portion of the second region of semiconductor material formed in step (b) are formed at a temperature on the order of 350°

C., and the remainder of the second region of semiconductor material formed in step (b) is formed at a temperature on the order of 450°

C.±

approximately 25°

C.

62. The method of claim 57 wherein the layer of low resistivity n-type semiconductor material is formed at a temperature in the range of 150°

C. to 200°

C.

63. The method of claims 59, 60 or 61 wherein the layer of low resistivity n-type semiconductor material is formed at a temperature in the range of 150°

C. to 200°

C.

64. The method of claims 50, 54, 55 or 57 wherein the first and second regions of semiconductor material formed in steps (a) and (b) are formed in an atmosphere maintained at 3-8×

10^-6 torr.

65. The method of claims 50, 54, 55 or 57 wherein an antireflective coating is formed on the grid-like contact and the exposed surface of the second semiconductor layer.

66. The method of claims 50, 54, 55 or 57 wherein an antireflective coating formed of SiO_x is formed on the grid-like contact and the exposed surface of the second semiconductor layer.

67. The method of claims 50, 54, 55 or 57 wherein an antireflective coating formed of SiO_x wherein "x" is on the order of "1.8" is formed on the grid-like contact and the exposed surface of the semiconductor layer.

68. The product produced by the method set forth in claims 50, 54, 55 or 57.

69. A p-n-type heterojunction photovoltaic device comprising, in combination:

a metallized substrate;

a first relatively thin-film region of relatively low resistivity p-type material adhered to said metallized substrate;

a second relatively thin-film region formed of the same elemental constituents as said relatively low resistivity p-type material and having been formed as a relatively high resistivity transient n-type material region with said relatively low resistivity p-type material and said relatively high resistivity transient n-type material region having been formed as a composite transient p-n-type homojunction semiconductor layer; and

, a relatively thin film of low resistivity n-type semiconductor material having been deposited on said transient p-n homojunction whereupon interdiffusion of the constituent elements of the materials defining said p-type region, said transient n-type region and said n-type semiconductor material between the p-type material and the transient n-type material, and between the transient n-type material and the n-type semiconductor material causes the transient n-type material to evolve into relatively high resistivity p-type material so as to form a thin-film heterojunction essentially devoid of growth nodules and permitting a photovoltaic response characteristic of energy transducers capable of exhibiting conversion efficiencies at least approximating 10.0%.

70. The device of claim 69 wherein said first and second regions of p-type and transient n-type material comprise a ternary semiconductor material.

71. The device of claim 70 wherein said ternary semiconductor material is a chalcopyrite compound.

72. The device of claim 70 wherein said ternary semiconductor material comprises a material selected from the class of I-III-VI₂ chalcopyrite compounds.

73. The device of claim 70 wherein said ternary semiconductor material is CuInSe₂.

74. The device of claim 73 wherein the copper/indium ratio in said first region of said ternary semiconductor material is such as to form a slightly copper-enriched first region of relatively low resistivity p-type material and the copper/indium ratio in said second region of said ternary semiconductor material is such as to form a slightly copper-deficient second region of relatively high resistivity transient n-type material.

75. The device of claim 74 wherein said first region of p-type material comprises between about 50% and about 66.7% of the total desired thickness of said transient p-n-type homojunction.

76. The device of claim 74 wherein said film of low resistivity n-type semiconductor material is CdS.

77. The device of claim 74 wherein said film of low-resistivity n-type semiconductor material comprises a first region of relatively pure CdS and a second superimposed region of indium-doped CdS.

78. The device of claim 69 wherein a grid-like contact is formed on the surface of said thin film of low resistivity n-type semiconductor material.

79. The device of claim 78 wherein an antireflective coating is formed on said grid-like contact and on the exposed surface of said thin film of low resistivity n-type semiconductor material.

80. The device of claim 79 wherein said antireflective coating comprises SiO_x wherein "x" is on the order of "1.8".

81. In a photovoltaic light-to-electrical energy transducer of the type comprising a thin-film p-n-type heterojunction including a metalized substrate, a first semiconductor layer formed of p-type semiconductor material deposited on said metallized substrate, a second semiconductor layer formed of low resistivity n-type semiconductor material formed on said first semiconductor layer, and a grid-like upper contact formed on said second semiconductor layer, the improvement wherein:

said first semiconductor layer includes a first region of low resistivity, p-type semiconductor material formed on said metallized substrate; and

a second region having been formed as a relatively high resistivity transient n-type semiconductor material region formed on said first region of p-type material with said first and second regions having been formed as a transient p-n-type homojunction formed on said metallized substrate with said transient n-type semiconductor region sandwiched between said low resistivity region of p-type semiconductor material and said second semiconductor layer formed of low resistivity n-type material so as to permit said transient n-type region to evolve through elemental interdiffusion into a region of relatively high resistivity p-type material so as to form a thin-film, p-n-type heterojunction photovoltaic light-to-electrical energy transducer.

82. The transducer of claim 81 wherein said first and second regions of p-type and transient n-type material comprise a ternary semiconductor material.

83. The transducer of claim 82 wherein said ternary semiconductor material is a chalcopyrite compound.

84. The transducer of claim 82 wherein said ternary semiconductor material comprises a material selected from the class of I-III-VI₂ chalcopyrite compounds.

85. The transducer of claim 82 wherein said ternary semiconductor material is CuInSe₂.

86. The transducer of claim 85 wherein the copper/indium ratio in said first region of said ternary semiconductor material is such as to form a slightly copper-enriched first region of relatively low resistivity p-type material and the copper/indium ratio in said second region of said ternary semiconductor material is such as to form a slightly copper-deficient second region of relatively high resistivity transient n-type material.

87. The transducer of claim 86 wherein said first region of p-type material comprises between about 50% and about 66.7% of the total desired thickness of said transient p-n-type homojunction.

88. The transducer of claim 86 wherein said second semiconductor layer formed of low resistivity n-type semiconductor material is CdS.

89. The transducer of claim 86 wherein said second semiconductor layer formed of low resistivity n-type semiconductor material comprises a first region of relatively pure CdS and a second superimposed region of indium-doped CdS.

90. The transducer of claim 81 wherein said grid-like upper contact formed on the surface of said second semiconductor layer is aluminum.

91. The transducer of claim 90 wherein an anti-reflective coating is formed on said grid-like conact and on the exposed surface of said second semiconductor layer.

92. The transducer of claim 91 wherein said antireflective coating comprises SiO_x wherein "x" is on the order of "1.8".

93. In a method of forming a photovoltaic light-to-electrical energy transducer of the type including a thin-film A-B-type heterojunction where "A" and "B" are selected from the group of semiconductor materials consisting of

View Dependent Claims (94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109)

94. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claim 93 wherein the transducer formed is heated during step (c) in the presence of air.

95. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claim 93 wherein the transducer formed is heated during step (c) in the presence of H₂ /Ar and air.

96. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94, or 95 wherein the transducer formed is heated during step (c) at a temperature on the order of 200°

C.

97. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the transducer formed is heated during step (c) at a temperature on the order of 200°

C. for a period on the order of 20 minutes.

98. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the A-B-type heterojunction is a p-n-type heterojunction and the one semiconductor layer defining the transient homojunction defines a transient p-n-type homojunction having a region of low resistivity p-type material and a region of high resistivity transient n-type material, and the other semiconductor layer is formed of n-type semiconductor material deposited in face-to-face contact with the region of high resistivity transient n-type material.

99. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the A-B-type heterojunction is an n-p-type heterojunction and the one semiconductor layer defining the transient homojunction defines a transient n-p-type homojunction having a region of high resistivity transient n-type material and a region of low resistivity p-type material, and the other semiconductor layer is formed on n-type semiconductor material deposited in face-to-face contact with the region of high resistivity transient n-type material.

100. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the ternary material is selected from the group of I-III-VI₂ chalcopyrite compounds.

101. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the ternary material is selected from the group of I-III-VI₂ chalcopyrite compounds and the other of the first and second semiconductor layers is formed of materials selected from the group of II-VI elements.

102. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the ternary semiconductor material is CuInSe₂.

103. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the other of the first and second semiconductor layers has a band gap energy greater than 1.5 ev.

104. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the other of the first and second semiconductor layers is selected from the group consisting of:

CdS;

Cd_1--x Zn_x S; and

,

CdS_1--x Se_x.

105. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the ternary semiconductor material is CuInSe₂ and the other of the first and second semiconductor layers is selected from the group consisting of:

CdS;

Cd_1--x Zn_x S; and

,

CdS_1--x Se_x.

106. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the ternary semiconductor material is CuInSe₂ and the other of the first and second semiconductor layers is CdS.

107. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the ternary semiconductor material is a I-III-VI₂ chalcopyrite compound and the ratio of the I-III-elements is adjusted during one portion only of simultaneous elemental evaporation of the ternary compound so as to form one of the low resistivity and transient high resistivity regions of the transient homojunction, and adjusted to a different I-III ratio during the remaining portion of simultaneous elemental evaporation of the ternary compound so as to form the other of the low resistivity and the transient high resistivity regions of the transient homojunction.

108. The method of forming a photovoltaic light-to-electrical energy transducer including a thin-film A-B-type heterojunction as set forth in claims 93, 94 or 95 wherein the ternary semiconductor layer is CuInSe₂ and the copper/indium ratio is initially adjusted to form a slightly copper-enriched region during simultaneous elemental evaporation of the CuInSe₂ to form the low resistivity region of the transducer of p-type material, and is readjusted to form a slightly copper-deficient region during simultaneous elemental evaporation of the CuInSe₂ to form the high resistivity transient semiconductor region of the transducer of transient n-type material.

109. The product produced by the method set forth in claims 93, 94 or 95.

110. The method of forming a p-n-type heterojunction photovoltaic device comprising the steps of:

(a) depositing a first region of relatively low resistivity p-type material on a metallized substrate;

(b) depositing a second region of relatively high resistivity transient n-type material formed of the same elemental constituents as the relatively low resistivity p-type material deposited in step (a) with such transient n-type material being deposited on the first region of p-type material and defining therewith a transient p-n-type homojunction;

(c) depositing a film of low resistivity n-type semiconductor material on the transient p-n-type homojunction formed in steps (a) and (b); and

,

(d) heating the p-n-type heterojunction photovoltaic device formed in steps (a), (b) and (c);

whereupon interdiffusion of the constituent elements of the materials employed in steps (a), (b) and (c) between the p-type material and the transient n-type material, and between the transient n-type material and the n-type semiconductor material, causes the transient n-type material to evolve into relatively high resistivity p-type material so as to form a thin-film heterojunction essentially devoid of growth nodules and providing a photovoltaic response characteristic of energy transducers having relatively high conversion efficiencies.

111. The method of claim 110 wherein the device formed is heated during step (d) in the presence of air.

112. The method of claim 110 wherein the device formed is heated during step (d) in the presence of H₂ /Ar and air.

113. The method of claims 110, 111 or 112 wherein the device formed is heated during step (d) at a temperature on the order of 200°

C.

114. The method of claims 110, 111 or 112 wherein the device formed is heated during step (d) at a temperature on the order of 200°

C. for a period on the order of 20 minutes.

115. The method of claim 110 wherein the first and second regions of p-type and transient n-type material, respectively, comprise a ternary semiconductor material formed by simultaneous elemental evaporation.

116. The method of claim 115 wherein the ternary semiconductor material is a chalcopyrite compound.

117. The method of claim 115 wherein the ternary semiconductor material is a material selected from the class of I-III-VI₂ chalcopyrite compounds.

118. The method of claim 115 wherein the ternary semiconductor material is CuInSe₂.

119. The method of claim 118 wherein the copper/indium ratio in the ternary semiconductor material is initially adjusted to form a slightly copper-enriched region during simultaneous elemental evaporation thereof to form the first region of relatively low resistivity p-type material in step (a) and is readjusted during such simultaneous elemental evaporation to form a slightly copper-deficient ternary compound during evaporation of the second region of relatively high resistivity transient n-type material formed in step (b).

120. The method of claim 118 wherein the copper/indium ratio is altered upon formation of at least about 50% of the total desired thickness of the transient p-n-type homojunction but prior to formation of about 66.7% of the total desired thickness of the transient p-n-type homojunction.

121. The method of claim 118 wherein the film of low resistivity n-type semiconductor material is formed of n-type material having a band gap energy greater than 1.5 ev.

122. The method of claim 121 wherein the n-type low resistivity semiconductor material is a II-VI material.

123. The method of claim 127 wherein the II-VI material is selected from the group consisting of:

CdS;

Cd_1--x Zn_x S; and

,

CdS_1--x Se_x.

124. The method of claim 122 wherein the II-VI material is CdS.

125. The method of claim 110 wherein the film of low-resistivity n-type semiconductor material comprises a first region of relatively pure CdS and a second superimposed region of indium-doped CdS.

126. The method of claim 110 wherein the first and second regions of semiconductor material formed in steps (a) and (b) are formed of a temperature in the range of 350°

C. to 500°

C.

127. The method of claim 110 wherein the first region of semiconductor material formed in step (a) and a portion of the second region of semiconductor material formed in step (b) are formed at a temperature in the range of 350°

C. to a temperature less than 450°

C., and the remainder of the second region of semiconductor material formed in step (b) is formed at a temperature in the range of about 450°

to 500°

C.

128. The method of claim 110 wherein the first region of semiconductor material formed in step (a) and a portion of the second region of semiconductor material formed in step (b) are formed at a temperature on the order of 350°

C., and the remainder of the second region of semiconductor material formed in step (b) is formed at a temperature on the order of 450°

C.±

approximately 25°

C.

129. The method of claim 110 wherein the film of low resistivity n-type semiconductor material formed in step (c) is formed at a temperature in the range of 150°

C. to 200°

C.

130. The method of claims 126, 127 or 128 wherein the film of low resistivity n-type semiconductor material formed in step (c) is formed at a temperature in the range of 150°

C. to 200°

C.

131. The method of claims 110, 116, 117, 118, 124, 132 or 133 wherein the first and second regions of semiconductor material formed in steps (a) and (b) are formed in an atmosphere maintained at 3-8×

10^-6 torr.

132. The method of claims 110, 116, 117 or 118 wherein a grid-like contact is formed on the film of low resistivity n-type semiconductor material deposited in step (c) and an antireflective coating is formed on the grid-like contact and the exposed surface of the film of low resistivity n-type semiconductor material.

133. The method of claims 110, 115, 116, 117 or 118 wherein a grid-like contact is formed on the film of low resistivity n-type semiconductor material deposited in step (c) and an antireflective coating formed of SiO_x is formed on the grid-like contact and the exposed surface of the film of low resistivity n-type semiconductor material.

134. The method of claims 110, 111, 117 or 118 wherein a grid-like contact is formed on the film of low resistivity n-type semiconductor material deposited in step (c) and an antireflective coating formed of SiO_x wherein "x" is on the order of "1.8" is formed on the grid-like contact and the exposed surface of the film of low resistivity n-type semiconductor material.

135. The product produced by the method set forth in claims 110, 115, 116, 117, 118, 119, 127, 128 or 129.

136. A thin-film A-B type heterojunction photovoltaic device wherein "A" and "B" are selected from the group of semiconductor materials consisting of:

space="preserve" listing-type="tabular">______________________________________ A AND B ______________________________________ (1) a p-type ternary material and an n-type material;

or, (2) an n-type ternary material and a p-type material;

or, (3) an n-type material and a p-type ternary material;

or, (4) a p-type material and an n-type ternary material;

______________________________________

comprising a first semiconductor layer .[.having been formed with a first region of A-type material and a second superimposed region of transient B-type material with said first and second regions initially defining a transient A-B-type homojunction, and a second semiconductor layer deposited on said first layer and formed of a second B-type material whereupon interdiffusion of the constituent elements defining;

(i) said A-type material;

(ii) said transient B-type material; and

(iii), said second B-type material;

causes the transient B-type material to evolve into A-type material so as to form a thin-film.]. .Iadd.formed of A-type material and a second superimposed semiconductor layer formed of B-type material deposited on said first layer;

one of said first and second semiconductor layers having been formed with a first region of ternary material comprising a selected one of a p-type ternary material or an n-type ternary material, and a second transient region of ternary material of the opposite conductivity type as that selected in said first region, said second transient region of ternary material being adjacent the other of said first and second semiconductor layers, with said first and second regions of said one of said first and second semiconductor layers initially defining a transient homojunction comprising one of a p-n-type or an n-p-type homojunction;

whereupon interdiffusion of the constituent elements defining;

(i) said first region of ternary material in said one of said first and second semiconductor layers respectively formed of A-type and B-type materials;

(ii) said second transient region of ternary material in said one of said first and second semiconductor layers; and

(iii), the other of said first and second semiconductor layers;

causes the second transient region of ternary material to evolve into a ternary material having the same p-type of n-type characteristic as said first region of ternary material so as to form a thin-film A-B-type .Iaddend.heterojunction permitting a photovoltaic response characteristic of an energy transducer capable of exhibiting a conversion efficiency approximating on the order of 10%.

137. The thin-film A-B-type heterojunction photovoltaic device set forth in claim 136 wherein said A-B-type heterojunction is a p-n-type heterojunction with said first semiconductor layer defining said transient .[.A-B-.]. homojunction having been formed as a transient p-n-type homojunction having a .Iadd.first .Iaddend.region of low resistivity p-type material and a .Iadd.second .Iaddend.region of high resistivity transient n-type material, and said second semiconductor layer is formed of n-type semiconductor material deposited in face-to-face contact with said .Iadd.second transient .Iaddend.region of high resistivity transient n-type material.

138. The thin-film A-B-type heterojunction photovoltaic device as set forth in claim 136 wherein said A-B-type heterojunction is an n-p-type heterojunction with said first semiconductor layer defining said transient .[.A-B.]. homojunction having been formed as a transient n-p-type homojunction having a .[.region of high resistivity transient n-type material and a region of low resistivity.]. .Iadd.first region of low resistivity n-type material and a second region of high resistivity transient .Iaddend.p-type material, and said second semiconductor layer is formed of .[.n-type.]. .Iadd.p-type .Iaddend.semiconductor material deposited in face-to-face contact with said .Iadd.second transient .Iaddend.region of high resistivity transient .[.n-type.]. .Iadd.p-type .Iaddend.material.

139. The thin-film A-B-type heterojunction photovoltaic .[.devive.]. .Iadd.device .Iaddend.as set forth in claim 136 wherein .[.said first semiconductor layer is formed of a.]. .Iadd.one of said first and second semiconductor layers is formed of first and second regions of .Iaddend.ternary material selected from the group of I-III-VI₂ chalcopyrite compounds.

140. The A-B-type heterojunction photovoltaic device as set forth in claim 136 wherein .[.said first semiconductor layer is formed of a.]. .Iadd.one of said first and second semiconductor layers is formed of first and second regions of .Iaddend.ternary material selected from the group of I-III-VI₂ chalcopyrite compounds and .[.said second semiconductor layer.]. .Iadd.the other of said first and second semiconductor layers .Iaddend.is formed of materials selected from the group of II-VI elements.

141. The thin-film A-B-type heterojunction photovoltaic device as set forth in claims 139 or 140 wherein said ternary material has a band gap energy in the range of 1-1.5 ev.

142. The thin-film A-B-type heterojunction photovoltaic device as set forth in claims 139 or 140 wherein said ternary material has a band gap energy in the range of 1-1.5 ev and .[.said second semiconductor layer is.]. .Iadd.the other of said first and second semiconductor layers is .Iaddend.formed of materials having a band gap energy greater than 1.5 ev.

143. The thin-film A-B-type heterojunction photovoltaic device as set forth in claims 136, 137 or 138 wherein said g .[.first semiconductor layer is formed of CuInSe₂..]. .Iadd.ternary material is CuInSe₂. .Iaddend.

144. The thin-film A-B-type heterojunction photovoltaic device as set forth in claims .[.141, 142 or 143.]. .Iadd.136, 137 or 138 .Iaddend.wherein .[.said second semiconductor layer.]. .Iadd.the other of said first and second semiconductor layers .Iaddend.has a band gap energy greater than 1.5 ev.

145. The thin-film A-B-type heterojunction photovoltaic device as set forth in claims 136, 137 or 138 wherein .[.said second semiconductor layer.]. .Iadd.the other of said first and second semiconductor layers .Iaddend.is formed of materials selected from the group consisting of:

CdS;

Cd_1--x Zn_x S; and

,

CdS_1--x Se_x.

146. The thin-film A-B-type heterojunction photovoltaic device as set forth in claims 136, 137 or 138 wherein .[.said first semiconductor is formed of a ternary semiconductor material comprising CuInSe₂ and said second semiconductor layer.]. .Iadd.one of said first and second semiconductor layers is formed of a ternary semiconductor material comprising CuInSe₂ and the other of said first and second semiconductor layers .Iaddend.is formed of materials selected from the group consisting of:

CdS;

Cd_1--x Zn_x S; and

,

CdS_1--x Se_x.

147. The thin-film A-B-type heterojunction photovoltaic device as set forth in claims 136, 137 or 138 wherein .[.said first semiconductor layer is formed of a ternary semiconductor material comprising CuInSe₂ and said second semiconductor layer is CdS..]. .Iadd.one of said first and second semiconductor layers is formed of a ternary semiconductor material comprising CuInSe₂ and the other of said first and second semiconductor layers is CdS. .Iaddend.