Producing thin film photovoltaic modules with high integrity interconnects and dual layer contacts

• US 6,077,722 A
• Filed: 07/14/1998
• Issued: 06/20/2000
• Est. Priority Date: 07/14/1998
• Status: Expired due to Fees

• Current Assignee: BP Solar International Incorporated (BP PLC)
• Original Assignee: BP SOLAREX (BP PLC)
• Inventors: Jansen, Kai W., Maley, Nagi
• Primary Examiner(s): CODD, BERNARD P
• Application Number:
  US09/115,316
• Time in Patent Office: 707 Days
• Field of Search: 438/74, 438/95, 438/96, 438/98, 136/249 MS, 136/249 TJ
• US Class Current: 438/74
• CPC Class Codes: B32B 17/10036 comprising two outer glass sheets
• CPC Class Codes: B32B 17/10788 containing ethylene vinylacetate
• CPC Class Codes: H01L 31/03921 including only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/046 PV modules composed of a plurality of thin film solar cells deposited on the same substrate
• CPC Class Codes: H01L 31/0463 characterised by special patterning methods to connect the PV cells in a module, e.g. laser cutting of the conductive or active layers
• CPC Class Codes: H01L 31/075 the potential barriers being only of the PIN type, e.g. amorphous silicon PIN solar cells
• CPC Class Codes: H01L 31/076 Multiple junction or tandem solar cells
• CPC Class Codes: H01L 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/1824 Special manufacturing methods for microcrystalline Si, uc-Si
• CPC Class Codes: H01L 31/202 including only elements of Group IV of the Periodic Table
• CPC Class Codes: Y02E 10/541 CuInSe2 material PV cells
• CPC Class Codes: Y02E 10/545 Microcrystalline silicon PV cells
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells
• CPC Class Codes: Y02E 10/548 Amorphous silicon PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

High performance photovoltaic modules are produced with improved interconnects by a special process. Advantageously, the photovoltaic modules have a dual layer back (rear) contact and a front contact with at least one layer. The front contact and the inner layer of the back contact can comprise a transparent conductive oxide. The outer layer of the back contact can comprise a metal or metal oxide. The front contact can also have a dielectric layer. In one form, the dual layer back contact comprises a zinc oxide inner layer and an aluminum outer layer and the front contact comprises a tin oxide inner layer and a silicon dioxide dielectric outer layer. One or more amorphous silicon-containing thin film semiconductors can be deposited between the front and back contacts. The contacts can be positioned between a substrate and an optional superstrate. During production, the transparent conductive oxide layer of the front contact is scribed by a laser, then the amorphous silicon-containing semiconductors and inner layer of the dual layer back contact are simultaneously scribed and trenched (drilled) by the laser and the trench is subsequently filled with the same metal as the outer layer of the dual layer back contact to provide a superb mechanical and electrical interconnect between the front contact and the outer layer of the dual layer back contact. The outer layer of the dual layer back contact can then be scribed by the laser. For enhanced environmental protection, the photovoltaic modules can be encapsulated.

Claims

1. A process for producing photovoltaic modules, comprising the steps of:

positioning a front contact on a substrate;

depositing at least one amorphous silicon-containing thin film semiconductor on said front contact;

depositing a transparent conductive layer of a dual layer back contact on said amorphous silicon-containing thin film semiconductor;

simultaneously laser scribing said transparent conductive layer of said dual layer back contact and said amorphous silicon-containing thin film semiconductor to form a trench through said transparent conductive layer of said dual layer contact and said amorphous silicon-containing thin film semiconductor; and

immediately thereafter;

depositing a layer of metal on said transparent conductive layer of said dual layer back contact and simultaneously filling said trench with said metal to form an interconnect extending between and connecting said front contact and said dual layer back contact.

2. A process in accordance with claim 1 wherein said front contact comprises a layer selected from the group consisting of a transparent metallic oxide layer and a dielectric layer, said transparent metallic oxide layer selected from the group consisting of tin oxide, indium-tin oxide, zinc oxide, and cadmium stannate;

and

said substrate selected from the group consisting of glass, stainless steel and metal.

3. A process in accordance with claim 1 wherein:

said transparent conductive oxide of said dual layer back contact is selected from the group consisting of tin oxide, indium-tin oxide, zinc oxide, and cadmium stannate; and

said metal layer is selected from the group consisting of aluminum, silver, molybdenum, platinum, steel, iron, niobium, titanium, chromium, bismuth, antimony, and oxides of the preceding.

4. A process in accordance with claim 1 wherein said amorphous silicon-containing thin film semiconductor comprises an amorphous silicon-containing material selected from the group consisting of hydrogenated amorphous silicon, hydrogenated amorphous silicon carbon, and hydrogenated amorphous silicon germanium.

5. A process in accordance with claim 1 wherein said photovoltaic modules comprise monolithic solar cells selected from the group consisting of single junction solar cells, multi-junction solar cells, tandem solar cells, and triple junction solar cells.

6. A process in accordance with claim 1 including depositing a conductive paste on said substrate, and heating and bonding said conductive paste to said substrate.

7. A process in accordance with claim 1 including laser scribing a pattern on said front contact.

8. A process in accordance with claim 1 including laminating a superstrate to said photovoltaic module by:

placing an encapsulating material on said dual layer back contact;

placing a superstrate on said encapsulating material, and

simultaneously subjecting said superstrate, said encapsulating material, and said photovoltaic module together by vacuum lamination.

9. A process for producing photovoltaic modules of monolithic multi-junction solar cells, comprising the steps of:

positioning a front contact comprising a transparent metallic oxide layer on a light-transmissive vitreous substrate;

said transparent metallic oxide layer comprising a front semiconductor selected from the group consisting of tin oxide, indium-tin oxide, zinc oxide, and cadmium stannate;

said light-transmissive vitreous substrate being selected from the group consisting of transparent glass and translucent glass;

depositing an amorphous silicon p-i-n cell comprising hydrogenated amorphous silicon above said transparent metallic oxide layer of said front contact by enhanced plasma chemical vapor deposition, including depositing a p₁ -layer above said front contact, an i₁ -layer on said p₁ -layer, and an n₁ -layer on said i₁ -layer, said amorphous silicon thin film semiconductor having a band gap ranging from 1.4 eV to 1.75 eV;

depositing an amorphous silicon germanium p-i-n cell comprising hydrogenated amorphous silicon germanium on said amorphous silicon p-i-n cell by enhanced plasma chemical vapor deposition, including depositing a p₂ -layer on said n₁ -layer, an i₂ -layer on said p₂ -layer, and an n₂ -layer on said i₂ -layer, said amorphous silicon p-i-n cell comprising an amorphous silicon germanium thin film semiconductor having a bandgap ranging from 1.4 eV to 1.6 eV;

depositing a dual layer back contact on said amorphous silicon germanium p-i-n cell, said dual layer back contact having an inner metallic layer and an outer metallic layer;

said inner metallic layer being deposited on said n₂ -layer by chemical vapor deposition, said inner metallic layer comprising a transparent conductive oxide selected from the group consisting of zinc oxide, tin oxide, indium-tin oxide, and cadmium oxide;

simultaneously laser scribing a trench through said inner metallic layer of said dual layer back contact, said amorphous silicon p-i-n cell and said amorphous silicon germanium p-i-n cell, such that said trench extends between said transparent metallic oxide layer of said front contact and said inner metallic layer of said back contact;

thereafter

depositing said outer metallic layer on said inner metallic layer, said outer metallic layer comprising a metal selected from the group consisting of aluminum, silver, molybdenum, platinum, steel, iron, niobium, titanium, chromium, bismuth, antimony, and oxides of the preceding; and

simultaneously

substantially filling said trench with said metal of said outer metallic layer of said back contact to form a metallic interconnect through said inner metallic layer of said dual layer contact, said amorphous silicon p-i-n cell and said amorphous silicon germanium p-i-n cell, said metallic interconnect extending between and mechanically and electrically connecting the transparent metallic oxide layer of said front contact to said inner metallic layer of said back contact.

10. A process in accordance with claim 9 wherein:

said inner metallic layer of said dual layer back contact comprises zinc oxide;

said outer metallic layer of said dual layer back contact comprises aluminum; and

said aluminum is deposited on said zinc oxide by sputtering.

11. A process in accordance with claim 10 including:

laser scribing a first pattern on said front semiconductor of said front contact; and

said transparent metallic oxide layer of said front semiconductor of said front contact comprises tin oxide.

12. A process in accordance with claim 11 wherein:

said front contact further comprises a dielectric layer;

said dielectric layer comprises silicon dioxide;

said tin oxide of said transparent metallic oxide of said front contact is deposited on said dielectric layer; and

said tin oxide of said transparent metallic oxide of said front contact being positioned between said p₁ -layer of said amorphous silicon p-i-n cell and said dielectric layer of said front contact.

13. A process in accordance with claim 11 including:

simultaneously laser scribing said amorphous silicon p-i-n cell, said amorphous silicon germanium p-i-n cell, and said zinc oxide of said inner metallic layer of said dual layer back contact, in a second pattern parallel to said first pattern on said tin oxide, for series interconnection between segments of the photovoltaic module, and forming said trench by laser scribing.

14. A process in accordance with claim 13 including laser scribing said aluminum of said outer metallic layer of said dual layer back contact in a third pattern parallel to said second pattern for isolating the segments of the photovoltaic module and providing a series interconnect between said aluminum and said zinc oxide of said dual layer back contact.

15. A process in accordance with claim 14 including laser scribing a perimeter around the photovoltaic module for electrically isolating the segments from each other except through the series interconnect and said interconnection.

16. A process in accordance with claim 15 electrically curing said photovoltaic module by generating a direct current across adjacent segments in a reverse bias orientation.

17. A process in accordance with claim 9 including:

placing an encapsulating material comprising ethylene vinyl acetate on said outer metallic layer of said back contact;

placing a light-transmissive vitreous superstrate on said ethylene vinyl acetate, said light-transmissive vitreous superstrate being selected from the group consisting of transparent glass, translucent glass and opaque glass; and

vacuum laminating said superstrate and said encapsulating material to said photovoltaic module.

18. A process in accordance with claim 9 including:

depositing fritted conductive paste on said substrate, said fritted, conductive paste comprising silver, organic solvents, and organic binders;

curing said fritted conductive paste by heating said paste in a furnace to remove said solvents and binders and to provide a film; and

bonding said film being to said substrate for collecting current and providing a solderable external connection.