Thin film photovoltaic panel and method

• US 5,022,930 A
• Filed: 06/20/1989
• Issued: 06/11/1991
• Est. Priority Date: 06/20/1989
• Status: Expired due to Fees

• Current Assignee: Photon Energy GMBH (Hitachi, Ltd.)
• Original Assignee: Photon Energy GMBH (Hitachi, Ltd.)
• Inventors: Ackerman, Bruce, Albright, Scot P., Jordan, John F.
• Primary Examiner(s): Weisstuch, Aaron
• Application Number:
  US07/369,181
• Time in Patent Office: 721 Days
• Field of Search: 136/251, 437/2-5, 437/207, 437/210, 437/221-224
• US Class Current: 136/251
• CPC Class Codes: H01L 31/0392 including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate textured substrates H01L31/02366
• CPC Class Codes: H01L 31/03925 including AIIBVI compound materials, e.g. CdTe, CdS
• CPC Class Codes: H01L 31/048 Encapsulation of modules
• CPC Class Codes: Y02E 10/543 Solar cells from Group II-VI materials

Abstract

A thin film photovoltaic panel includes a backcap for protecting the active components of the photovoltaic cells from adverse environmental elements. A spacing between the backcap and a top electrode layer is preferably filled with a desiccant to further reduce water vapor contamination of the environment surrounding the photovoltaic cells. The contamination of the spacing between the backcap and the cells may be further reduced by passing a selected gas through the spacing subsequent to sealing the backcap to the base of the photovoltaic panels, and once purged this spacing may be filled with an inert gas. The techniques of the present invention are preferably applied to thin film photovoltaic panels each formed from a plurality of photovoltaic cells arranged on a vitreous substrate. The stability of photovoltaic conversion efficiency remains relatively high during the life of the photovoltaic panel, and the cost of manufacturing highly efficient panels with such improved stability is significantly reduced.

Claims

1. An improved stability photovoltaic panel, comprising a plurality of photovoltaic cells each having a plurality of polycrystalline thin film layers, each of the plurality of thin film layers respectively deposited on a common vitreous substrate for allowing light to pass therethrough to reach a photovoltaic hetrojunciton formed by at least two of the plurlaity of thin film layers, at least one of the film layrs forming the photovoltaic heterojunction for each of the plurlaity of photovoltaic cells, each of the photovoltaic cells lying within a plane substantially parallel to an interior planar surface of the vitreous substrate, each of the photovoltaic cells being connected electrically in series to pass electrical current from the photovoltaic panel, a pliable sheet material backcap opposite the vitreous substrate with respect to the plurality of photovoltaic cells and spaced from the plurality of photovoltaic cells so as to form a substantially planar spacing between the plurality of photovoltaic cells and an interior surface of the sheet material backcap, a perimeter portion of the sheet material backcap having a bend for positioning an edge strip of the sheet material backcap spaced from the interior surface of the backcap to form the planar spacing, the edge strip forming a planar surface parallel with an sealingly engaging the vitreous substrate for forming a fluid-tight seal with the vitreous substrate about the perimeter of the plurality of photovoltaic cells for protecting the plurality of photovoltaic cells from elements exterior of the photovoltaic panel, and a selected desiccant filling substantially the planar spacing for preventing water vapor within the planar spacing from adversely affecting the plurality of photovoltaic cells.

2. The photovoltaic panel as defined in claim 1, wherein the selected desiccant is thermally conductive for transmitting heat from the plurality of photovoltaic cells to the sheet metal material backcap.

3. The photovoltaic panel as defined in claim 1, wherein the vitreous substrate includes an electrically conductive thin film layer formed on an interior surface of the vitreous substrate.

4. The photovoltaic panel as defined in claim 1, further comprising:

the fluid-tight seal is a semi-hermetic perimeter seal between the sheet material backcap and the vitreous substrate; and

a pliable adhesive for forming the semi-hermetic perimeter seal between the sheet material backcap and the vitreous substrate.

5. The photovoltaic panel as defined in claim 1, wherein the sheet material backcap lies substantially within a plane parallel to an interior surface of the vitreous substrate.

6. The photovoltaic panel as defined in claim 1, further comprising:

a sealable fluid input port for passing a purging gas through the sheet material backcap and into the spacing; and

a sealable fluid egress port for simultaneously passing the purging gas from the spacing past the sheet material backcap.

7. An improved stability photovoltaic panel comprising:

a plurality of photovoltaic cells each having a plurality of polycrystalline thin film layers;

each of the plurality of thin film layers deposited respectively on a common vitreous substrate for allowing light to pass therethrough to reach a photovoltaic heterojunction formed by at least two of the plurality of thin film layers;

each of the photovoltaic cells being connected electrically in series to pass electrical current from the photovoltaic panel;

a hermetic sheet material backcap opposite the vitreous substrate with respect tot eh plurality of photovoltaic cells and spaced from the plurality of photovoltaic cells to form a spacing between the plurality of photovoltaic cells and an interior surface of the sheet material backcap;

the sheet material backcap forming a fluid-tight seal with the vitreous substrate about the perimeter of the plurality of photovoltaic cells for protecting the plurality of photovoltaic cells from elements exterior of the photovoltaic panel;

a sealable fluid input port for passing a purging gas through the sheet material backcap and into the spacing; and

a sealable fluid egress port for simultaneously passing the purging gas from the spacing past the sheet material backcap.

8. The photovoltaic panel as defined in claim 7, wherein the sealable fluid input port comprises:

a fluid conduit having a fluid flow path and passing through the sheet material backcap;

an exterior surface of the fluid conduit being hermetically sealed with the sheet material backcap; and

the flow path within the fluid conduit being in fluid communication with the spacing and hermetically sealed from the exterior of the photovoltaic panel.

9. The photovoltaic panel as defined in claim 7, further comprising:

the sealable fluid input port includes a first electrically conductive fluid conduit;

the sealable fluid egress port includes a second electrically conductive fluid conduit;

elongate pliable wire conductors within the spacing and each interconnected electrically at one end to the plurality of photovoltaic cells and interconnected electrically at the respective other ends to the first and second electrically conductive conduits;

a pair of output wires each connected at one end to a respective one of the first and second conduits, such that one of the conduits represents and electrically positive conductor of the photovoltaic panel and the other of the conduits represents an electrically negative conductor of the photovoltaic panel.

10. The photovoltaic panel as defined in claim 7, wherein the spacing between the sheet material backcap and the plurality of photovoltaic cells is substantially filled with a selected desiccant for preventing water vapor within the spacing from deleteriously affecting the plurality of photovoltaic cells.

11. The photovoltaic panel as defined in claim 10, wherein the selected desiccant is thermally conductive for transmitting heat from the plurality of photovoltaic cells to the sheet material backcap.

12. The photovoltaic panel as defined in claim 7, wherein a perimeter portion of the sheet material backcap is in sealing engagement with the vitreous substrate and the sheet material backcap lies substantially within a plane parallel to an interior surface of the vitreous substrate.

13. The photovoltaic panel as defined in claim 7, wherein at least two of the thin film layers of each of the plurality of photovoltaic cells lie within a substantially horizontal plane parallel to an interior surface of the vitreous substrate.

14. The photovoltaic panel as defined in claim 7, wherein each of the photovoltaic cells includes a thin film layer consisting essentially of cadmium telluride.

15. The photovoltaic panel as defined in claim 14, wherein each of the photovoltaic cells includes another thin film layer consisting essentially of caldium sulfide.

16. The photovoltaic panel as defined in claim 7, wherein each of the photovoltaic cells is a substantially planar elongate strip formed on the vitreous substrate and spaced from an adjacent strip by an electrical connection to connect the strips electrically in a series.

17. The photovoltaic panel as defined in claim 16, wherein the electrical connection between the adjacent strips is a conductive thin film layer having a first portion adjacent the vitreous substrate and a second portion opposite the vitreous substrate with respect to the first portion.

18. The photovoltaic panel as defined in claim 7, wherein the sheet material backcap is sealed to the vitreous substrate by a pliable adhesive for dampening stresses between the sheet material backcap and the vitreous substrate attributable to thermal expansion, the adhesive forming a semi-hermetic seal between the sheet material backcap and the vitreous substrate.

19. The photovoltaic panel as defined in claim 7, wherein the sheet material backcap has a thickness of from 2 mils to 8 mils.

20. A method of improving the stability of a photovoltaic panel including a plurality of photovoltaic cells each having a plurality of polycrystalline thin film layers, each of the plurality of thin film layers respectively deposited on a common vitreous substrate for allowing light to pass therethrough to reach a photovoltaic heterojunction formed by at least two of the plurality of thin film layers, the method comprising:

electrically connecting each of the plurality of photovoltaic cells in series for passing electrical current from the photovoltaic panel;

positioning a hermetic sheet material backcap opposite the substrate with respect tot he plurality of photovoltaic cells and spaced from the plurality of photovoltaic cells so as to form the spacing therebetween;

filling substantially the entirety of the spacing with a selected desiccant for preventing water vapor within the spacing from deleteriously effecting the plurality of photovoltaic cells; and

sealingly engaging a perimeter portion of the sheet material backcap in a fluid-tight manner to the vitreous substrate about the perimeter of the plurality of photovoltaic cells for protecting the plurality of photovoltaic cells form elements exterior of the photovoltaic panel.

21. The method of forming a photovoltaic panel as defined in claim 20, further comprising:

adhering the selected desiccant to an interior surface of the sheet material backcap prior to positioning the backcap opposite the substrate with respect to the plurality of photovoltaic cells.

22. The method of forming a photovoltaic panel as defined in claim 20, wherein the vitreous substrate is glass having its interior surface coating with an electrically conductive film.

23. The method of forming a photovoltaic panel as defined in claim 20, wherein the material for the sheet material backcap is selected from a metal alloy including a metal selected from the group consisting of nickel and titanium.

24. The method of forming a photovoltaic panel as defined in claim 20, wherein the step of sealingly engaging a perimeter portion of the sheet material backcap to the vitreous substrate comprises:

applying an adhesive to a sealing surface of the vitreous substrate; and

curing the adhesive material to form a semi-hermetic seal between the vitreous substrate and the sheet material backcap, the cured adhesive being pliable for reducing stresses between the vitreous substrate and the sheet material backcap.

25. The method of forming a photovoltaic panel as defined in claim 20, wherein the step of sealingly engaging a perimeter portion of the sheet material backcap to the vitreous substrate comprises:

selecting a material for at least the perimeter of the sheet material backcap as a function of its coefficient of thermal expansion and the coefficient of thermal expansion of a sealing surface of the vitreous substrate; and

forming a hermetic seal between the sheet material backcap and the vitreous substrate.

26. The method of forming a photovoltaic panel as defined in claim 20, further comprising:

forming a bend in the perimeter portion of the sheet material backcap for positioning an edge strip of the sheet material backcap spaced from an interior surface of the backcap to form the spacing; and

forming a planar surface on the edge strip parallel with the substrate for sealingly engaging the substrate.

27. The method of forming a photovoltaic panel as defined in claim 20, further comprising:

forming a gas input port through the sheet material backcap for passing a a purging gas into the spacing;

forming a gas egress port through the sheet material backcap for passing a purging gas from the spacing;

purging the spacing with the purging gas by inputting the gas through the gas input port while exhausting the gas from the gas egress port; and

thereafter sealing the gas input port and the gas egress port.

28. The method of forming a photovoltaic panel as defined in claim 27, further comprising:

the step of sealingly engaging a perimeter portion of the sheet material backcap to the vitreous substrate includes curing a bond between the perimeter of the sheet material backcap and the vitreous substrate; and

the step of purging the spacing with the purging gas occurs throughout the time of curing the bond between the perimeter of the sheet material backcap and the vitreous substrate.

36. The method of forming a photovoltaic panel as defined in claim 28, wherein the vitreous substrate is glass having its interior surface coated with an electrically conductive film.

29. A method of improving the stability of a photovoltaic panel including a plurality of photovoltaic cells each having a plurality of polycrystalline thin film layers, each of the plurality of thin film layers respectively deposited on a vitreous substrate for allowing light to pass therethrough to reach a photovoltaic heterojunction formed by at least two of the plurality of thin film layers, the method comprising:

electrically connecting each of the plurality of photovoltaic cells in series for passing electrical current from the photovoltaic panel;

positioning a hermetic sheet material backcap opposite the substrate with respect to the plurality of photovoltaic cells and spaced from the plurality of photovoltaic cells so as to form a spacing therebetween;

sealing the sheet material backcap in a fluid-tight manner to the vitreous substrate about the perimeter of the plurality of photovoltaic cells for protecting the plurality of photovoltaic cells from elements exterior of the photovoltaic panel;

forming a gas input port for passing a purging gas through the sheet material backcap and into the spacing;

forming a gas egress port for simultaneously passing the purging gas from the spacing past the sheet material backcap;

thereafter passing a purging gas into the sealed spacing to remove deleterious fluid therefrom; and

thereafter sealing both the fluid input port and the fluid egress port.

30. The method of forming a photovoltaic panel as defined in claim 29, wherein:

the step f sealing the backcap to the vitreous substrate includes the steps of (a) placing an adhesive between the perimeter of the backcap and the vitreous substrate, and (b) subsequently curing the adhesive; and

the step of introducing the purging gas is performed during at least some stage of the adhesive curing process.

31. The method of forming a photovoltaic panel as defined in claim 29, further comprising:

introducing a selected gas into the spacing subsequent to the step of passing a purging gas into the spacing and prior to sealing the fluid port to protect the plurality of photovoltaic cells from elements exterior of the photovoltaic panel.

32. The method as defined in claim 31, wherein the selected gas is an inert gas selected from a group consisting of nitrogen, argon, and helium.

33. The method as defined in claim 29, further comprising:

filling substantially the entirely of the spacing with a selected desiccant for preventing water vapor within the spacing from deleteriously affecting the plurality of photovoltaic cells.

34. The method of forming a photovoltaic panel as defined in claim 33, further comprising:

adhering the selected desiccant to an interior surface of the sheet material backcap prior to positioning the backcap opposite the substrate with respect to the plurality of photovoltaic cells.

35. The method of forming a photovoltaic panel as defined in claim 33, wherein the selected desiccant is thermally conductive for transmitting heat from the plurality of photovoltaic cells to the sheet material backcap.

37. The method of forming a photovoltaic panel as defined in claim 29, wherein the material for the sheet material backcap is selected from a metal alloy including a metal selected from the group consisting of nickel and titanium.

38. The method of forming a photovoltaic panel as defined in claim 29, wherein the step of sealing the sheet material backcap to the vitreous substrate comprises:

applying an adhesive to a sealing surface of the vitreous substrate; and

curing the adhesive material to form a semi-hermetic seal between the vitreous substrate and the sheet material backcap, the cured adhesive being pliable for reducing stresses between the vitreous substrate and the sheet material backcap.

39. The method of forming a photovoltaic panel as defined in claim 29, wherein the step of sealing the sheet material backcap to the vitreous substrate comprises

selecting a material for at least the perimeter of the sheet material backcap as a function of its coefficient of thermal expansion and the coefficient of thermal expansion of the sealing surface of the vitreous substrate;

and

forming a hermetic seal between the sheet material backcap and the vitreous substrate.

40. The method of forming a photovoltaic panel as defined in claim 29, further comprising:

each of the gas input port and the gas output port being formed form a electrically conductive conduit passing through the sheet material backcap and having a flow path in fluid communication with the spacing and hermetically sealed form the exterior of the photovoltaic panel, such that one of the electrically conductive conduits serves as a respective electrically positive conductor of the photovoltaic panel and the other of the electrically conductive conduits serves as an electrically negative conductor of the photovoltaic panel.

41. The method of forming a photovoltaic panel as defined in claim 29, wherein each of the photovoltaic cells includes a film layer consisting essentially of cadmium telluride.

42. The method of forming a photovoltaic panel as defined in claim 29, further comprising:

forming each of the photovoltaic cells in a substantially planar elongate strip on the vitreous substrate and spaced from the adjacent strip by an electrical connection to connect the strips electrically in series; and

connecting adjacent strips electrically in series by depositing a conductive thin film layer between adjacent strips, the conductive thin film layer having a first portion adjacent the vitreous substrate and a second portion opposite the vitreous substrate with the respect to the first portion.