Apparatus and processes for the massproduction of photovotaic modules

• US 6,423,565 B1
• Filed: 05/30/2000
• Issued: 07/23/2002
• Est. Priority Date: 05/30/2000
• Status: Active Grant

• Current Assignee: Colorado State University Research Foundation
• Original Assignee: Kurt L. Barth, Robert A. Enzenroth, Walajabad S. Sampath
• Inventors: Enzenroth, Robert A., Sampath, Walajabad S., Barth, Kurt L.
• Primary Examiner(s): Everhart, Caridad
• Application Number:
  US09/583,381
• Time in Patent Office: 784 Days
• Field of Search: 438/57, 438/58, 438/59, 438/60, 438/61, 438/62, 438/63, 438/95, 438/603, 427/255.31, 427/126.1, 136/260, 136/264, 117/109
• US Class Current: 438/57
• CPC Class Codes: H01L 31/1828 the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
• CPC Class Codes: Y02E 10/543 Solar cells from Group II-VI materials

Abstract

An apparatus and processes for large scale inline manufacturing of CdTe photovoltaic modules in which all steps, including rapid substrate heating, deposition of CdS, deposition of CdTe, CdCl₂ treatment, and ohmic contact formation, are performed within a single vacuum boundary at modest vacuum pressures. A p+ ohmic contact region is formed by subliming a metal salt onto the CdTe layer. A back electrode is formed by way of a low cost spray process, and module scribing is performed by means of abrasive blasting or mechanical brushing through a mask. The vacuum process apparatus facilitates selective heating of substrates and films, exposure of substrates and films to vapor with minimal vapor leakage, deposition of thin films onto a substrate, and stripping thin films from a substrate. A substrate transport apparatus permits the movement of substrates into and out of vacuum during the thin film deposition processes, while preventing the collection of coatings on the substrate transport apparatus itself.

Claims

1. A method for fabricating semiconductor layers of a photovoltaic cell, all of the steps of which are carried out in a single vacuum chamber at a constant vacuum level, the method comprising the steps of:

providing, in the vacuum chamber, a substrate upon which the photovoltaic cell is to be fabricated;

heating the substrate to a desired temperature in the vacuum chamber;

depositing one or more layers of n-type IIB/VIB semiconductor material onto a surface of the substrate in the vacuum chamber;

depositing one or more layers of p-type IIB/VIB semiconductor material onto the one or more layers of n-type IIB/VIB semiconductor material in the vacuum chamber;

treating the one or more layers of n-type IIB/VIB and p-type IIB/VIB semiconductor material with a halogen containing substance in the vacuum chamber; and

forming an ohmic contact on the treated one or more layers of p-type IIB/VIB semiconductor material in the vacuum chamber by depositing a metal compound onto the treated one or more layers of p-type IIB/VIB semiconductor material and then annealing the treated one or more layers of p-type IIB/VIB semiconductor material.

2. A method as in claim 1, wherein the n-type semiconductor material comprises cadmium sulfide.

3. A method as in claim 1, wherein the p-type semiconductor material comprises cadmium telluride.

4. A method as in claim 1, wherein the halogen containing substance comprises cadmium chloride.

6. A method as in claim 1, further comprising the step of depositing an anti-reflective layer on an opposite surface of the substrate in the vacuum chamber.

7. A method as in claim 1, further comprising the step of treating the one or more layers of n-type IIB/VIB semiconductor material with the halogen containing substance prior to depositing the one or more layers of p-type IIB/VIB semiconductor material.

8. A method as in claim 7, wherein the halogen containing substance comprises cadmium chloride.

9. A method a s in claim 7, wherein the step of treating the one or more layers of n-type IIB/VIB semiconductor material with the halogen containing substance comprises:

exposing the one or more layers of n-type IIB/VIB semiconductor material to the vapor of the halogen containing substance for a predetermined time at a specific temperature; and

annealing the one or more layers of n-type IIB/VIB semiconductor material previously exposed to the- vapor of the halogen contain substance.

10. A method as in claim 9, wherein:

the temperature at which the one or more layers of n-type IIB/VIB semiconductor material is exposed to the vapor of the halogen containing substance is suitable for depositing a film of the halogen containing substance onto the one or more layers of n-type IIB/VIB semiconductor material; and

the step of annealing the one or more layers of n-type IIB/VIB semiconductor material is performed at a temperature suitable for treating the one or more layers of n-type IIB/VIB semiconductor material and removing the previously deposited film of the halogen containing substance.

11. A method as in claim 1, wherein the step of treating the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material with a halogen containing substance comprises:

exposing the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material to the vapor of the halogen containing substance for a predetermined time at a specific temperature; and

annealing the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material that have been exposed to the vapor of the halogen containing substance.

12. A method as in claim 1, wherein:

the temperature at which the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material are exposed to the vapor of the halogen containing substance is suitable for depositing a film of the halogen containing substance onto the one or more layers of p-type IIB/VIB semiconductor material; and

the step of annealing the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material is performed at a temperature suitable for treating the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material and removing the previously deposited film of the halogen containing substance.

13. A method as in claim 1, wherein the metal compound is a metal salt selected from the group comprising the salts of copper, silver, gold, tin, lead, antimony, and mercury.

14. A method as in claim 1, wherein the metal compound is an organometallic compound selected from the group comprising the organometallic compounds of copper, silver, gold, tin, lead, antimony, and mercury.

5. A method as in clam 1, further comprising the step of depositing in the vacuum chamber a layer of a transparent conductive oxide onto the substrate prior to the step of depositing the one or more layers of n-type IIB/VIB semiconductor onto the substrate .

15. A method for forming an ohmic contact on one or more layers of p-type IIB/VIB semiconductor material, the method comprising the steps of:

depositing a metal compound onto the one or more layers of p-type IIB/VIB semiconductor material in the vacuum chamber; and

annealing the one or more layers of p-type IIB/VIB semiconductor material in the vacuum chamber.

16. A method as in claim 15, wherein the step of annealing the one or more layers of p-type IIB/VIB semiconductor material in the vacuum chamber comprises heating said one or more layers of p-type IIB/VIB semiconductor material in a suitable gas.

17. A method as in claim 15, wherein the one or more layers of p-type IIB/VIB semiconductor material comprises cadmium telluride.

18. A method as in claim 15, wherein the metal compound is a metal salt selected from the group comprising the salts of copper, silver, gold, tin, lead, antimony, and mercury.

19. A method as in claim 15, wherein the metal compound is an organometallic compound selected from the group comprising the organometallic compounds of copper, silver, gold, tin, lead, antimony, and mercury.

20. A method for fabricating semiconductor layers of a photovoltaic cell all of the steps of which are carried out in a single vacuum chamber at a constant vacuum level, the method comprising the steps of:

providing, in the vacuum chamber, a substrate having one or more layers of an n-type transparent conductive oxide upon which the photovoltaic cell is to be fabricated;

heating the substrate to a desired temperature in the vacuum chamber;

depositing one or more layers of p-type IIB/VIB semiconductor material onto a surface of the substrate in the vacuum chamber;

treating the one or more layers of n-type transparent conductive oxide and p-type IIB/VIB semiconductor material with a halogen containing substance in the vacuum chamber; and

forming an ohmic contact on the treated one or more layers of p-type IIB/VIB semiconductor material in the vacuum chamber.

21. A method as in claim 20, wherein the p-type IIB/VIB semiconductor material comprises cadmium telluride.

22. A method as in claim 20, wherein the halogen containing substance comprises cadmium chloride.

23. A method as in claim 20, wherein the step of treating the one or more layers of n-type transparent conductive oxide and p-type IIB/VIB semiconductor material with a halogen containing substance comprises:

exposing the one or more layers of n-type transparent conductive oxide and p-type IIB/VIB semiconductor material to the vapor of the halogen contain substance for a predetermined time at a specific temperature; and

annealing the one or more layers of n-type transparent conductive oxide and p-type IIB/VIB semiconductor material that have been previously exposed to the vapor of the halogen containing substance.

24. A method as in claim 23, wherein:

the temperature at which the one or more layers of n-type transparent conductive oxide and p-type IIB/VIB semiconductor material are exposed to the vapor of the halogen containing substance is suitable for depositing a film of the halogen containing substance onto the one or more layers of p-type IIB/VIB semiconductor material; and

the step of annealing the one or more layers of n-type transparent conductive oxide and p-type IIB/VIB semiconductor material is performed at a temperature suitable for treating the one or more layers of n-type transparent conductive oxide and p-type IIB/VIB semiconductor material and removing the film of the previously deposited halogen containing substance.

25. A method as in claim 20, wherein the step of forming an ohmic contact on the treated one or more layers of p-type IIB/VIB semiconductor material comprises depositing a metal compound onto the treated one or more layers of p-type semiconductor material and then annealing the treated one or more layers of p-type IIB/VIB semiconductor material.

27. A method as in claim 25, wherein the metal compound is an organometallic compound selected from the group comprising the organometallic compounds of copper, silver, gold, tin, lead, antimony, and mercury.

28. A method as in claim 20, further comprising the step of depositing an anti-reflective layer on an opposite surface of the substrate in the vacuum chamber.

26. A method as in 25, wherein the metal compound is a metal salt selected from the group comprising the salts of copper, silver, gold, tin, lead, antimony and mercury.

29. A method for fabricating semiconductor layers of a photovoltaic cell all of the steps of which are carried out in a single vacuum chamber at a constant vacuum level, the method comprising the steps of:

providing, in the vacuum chamber, a substrate upon which the photovoltaic cell is to be fabricated, the substrate having one or more layers of n-type transparent conductive oxide thereon and one or more layers of n-type IIB/VIB semiconductor material on top of the one or more layers of n-type transparent conductive oxide;

heating the substrate to a desired temperature in the vacuum chamber;

depositing one or more layers of p-type IIB/VIB semiconductor material onto a surface of the substrate in the vacuum chamber;

treating the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material with a halogen containing substance in the vacuum chamber; and

forming an ohmic contact on the treated one or more layers of p-type IIB/VIB semiconductor material in the vacuum chamber.

30. A method as in claim 29, wherein the n-type IIB/VIB semiconductor material comprises cadmium sulfide.

31. A method as in claim 29, wherein the p-type IIB/VIB semiconductor material comprises cadmium telluride.

32. A method as in claim 29, wherein the halogen containing substance comprises cadmium chloride.

33. A method as in claim 29, wherein the step of treating the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material with a halogen containing substance comprises:

exposing the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material to the vapor of the halogen contain substance for a predetermined time at a specific temperature; and

annealing the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material that have been previously exposed to the vapor of the halogen containing substance.

34. A method as in claim 33, wherein:

the temperature at which the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material are exposed to the vapor of the halogen containing substance is suitable for depositing a film of the halogen containing substance upon the one or more layers of p-type IIB/VIB semiconductor material; and

the step of annealing the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material is performed at a temperature suitable for treating the one or more layers of n-type IIB/VIB semiconductor material and p-type IIB/VIB semiconductor material and removing the film of the previously deposited halogen containing substance.

35. A method as in claim 29, wherein the step of forming an ohmic contact on the treated one or more layers of p-type IIB/VIB semiconductor material comprises depositing a metal compound onto the treated one or more layers of type IIB/VIB semiconductor material and then annealing the treated one or more layers of p-type IIB/VIB semiconductor material.

36. A method as in claim 35, wherein the metal compound is a metal salt selected from the group comprising the salts of copper, silver, gold, tin, lead, antimony, and mercury.

37. A method as in claim 35, wherein the metal compound is an organometallic compound selected from the group comprising the organometallic compounds of copper, silver, gold, tin, lead, antimony, and mercury.

38. A method as in claim 29, further comprising the step of depositing an anti-reflective layer on an opposite surface of the substrate in the vacuum chamber.

39. A method as in claim 29, further comprising the step of treating the one or more layers of n-type IIB/VIB semiconductor material with a halogen containing substance prior to depositing the one or more layers of p-type IIB/VIB semiconductor material.

40. A method as in claim 39, wherein the halogen containing substance comprises cadmium chloride.

41. A method as in claim 39, wherein the step of treating the one or more layers of n-type IIB/VIB semiconductor material with a halogen containing substance comprises:

exposing the one or more layers of n-type IIB/VIB semiconductor material to the vapor of the halogen containing substance for a predetermined time at a specific temperature; and

annealing the one or more layers of n-type IIB/VIB semiconductor material that has been previously exposed to the vapor of the halogen containing substance.

42. A method as in claim 39, wherein:

the temperature at which the one or more layers of n-type IIB/VIB semiconductor material is exposed to the vapor of the halogen containing substance is suitable for depositing a film of the halogen containing substance onto the one or more layers of n-type IIB/VIB semiconductor

the step of annealing the one or more layers of n-type IIB/VIB semiconductor material is performed at a temperature suitable for treating the one or more layers of n-type IIB/VIB semiconductor material and removing the film of the preciously deposited halogen containing substance.