Polyimide resin composition for use in forming reverse reflecting layer in photovoltaic cell and method of forming reverse reflecting layer in photovoltaic cell used therewith

• US 9,287,424 B2
• Filed: 09/20/2011
• Issued: 03/15/2016
• Est. Priority Date: 09/21/2010
• Status: Active Grant

• Current Assignee: PI R&D Co.,Ltd.
• Original Assignee: PI R&D Co.,Ltd.
• Inventors: Win, Maw Soe, Goshima, Toshiyuki, Sato, Takahiro, Takato, Hidenao, Sakata, Isao
• Primary Examiner(s): Garber, Charles
• Assistant Examiner(s): Paterson, Brigitte
• Application Number:
  US13/822,955
• Publication Number:
  US 20130310482A1
• Time in Patent Office: 1,638 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: C08G 73/1039 comprising halogen-containing substituents
• CPC Class Codes: C08G 73/1042 Copolyimides derived from at least two different tetracarboxylic compounds or two different diamino compounds
• CPC Class Codes: C08G 73/1046 Polyimides containing oxygen in the form of ether bonds in the main chain
• CPC Class Codes: C08G 73/106 containing silicon
• CPC Class Codes: C08G 73/1064 containing sulfur
• CPC Class Codes: C08G 73/1067 Wholly aromatic polyimides, i.e. having both tetracarboxylic and diamino moieties aromatically bound
• CPC Class Codes: C08G 73/1071 Wholly aromatic polyimides containing oxygen in the form of ether bonds in the main chain
• CPC Class Codes: C08K 3/22 of metals
• CPC Class Codes: C08L 2203/204 use in solar cells
• CPC Class Codes: C09D 179/08 Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
• CPC Class Codes: H01L 31/02327 the optical elements being integrated or being directly associated to the device, e.g. back reflectors optical coatings H01L31/0216
• CPC Class Codes: H01L 31/056 the light-reflecting means being of the back surface reflector [BSR] type
• CPC Class Codes: Y02E 10/52 PV systems with concentrators
• CPC Class Codes: Y02E 10/546 Polycrystalline silicon PV cells
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells

Abstract

Disclosed are a method of forming a back reflection layer in a solar cell, a composition used therefor, and a solar cell having a back reflection layer formed by the method, which layer has superior heat-resistance and various types of durabilities, and can contribute to improving the conversion rate of solar cells and reliability during long-term use, and which method can form a back reflection layer in a solar cell easily and at low cost. The polyimide resin composition for use in forming a back reflection layer in a solar cell includes an organic solvent, a polyimide resin dissolved in the organic solvent, and light-reflecting particles dispersed in the organic solvent.

Claims

1. A method of forming a back reflection layer in a solar cell, said method comprising

coating a base layer on the back surface of said solar cell with a polyimide resin composition comprising an organic solvent, a polyimide resin having at least one group selected from the group consisting of alkyl groups and perfluoroalkyl groups in recurring units thereof, said polyimide resin being dissolved in said organic solvent, and light-reflecting metal oxide particles selected from the group consisting of silica (SiO₂), zirconia (ZrO₂), tantalum(V) oxide (Ta₂O₂), titanium oxide (TiO₂), zinc oxide (ZnO₂), and vanadium dioxide (VO₂), said particles being dispersed in said organic solvent, wherein said organic solvent is a mixed solvent comprising a hydrophobic organic solvent having a vapor pressure at room temperature of 1 mm Hg or lower and a hydrophilic organic solvent having a vapor pressure at room temperature of 1 mm Hg or lower, and

drying the resultant to form a polyimide film.

2. The method according to claim 1, wherein said polyimide film is formed by screen printing method, ink jet method or dispense method.

3. The method according to claim 1, wherein a polyimide film having a thickness of 1 μ

m or more after drying is formed by one coating.

4. The method according to claim 1, wherein said solar cell comprises:

a crystalline silicon substrate having a first conductivity type, which is composed of a single crystalline silicon or a polycrystalline silicon;

an impurity-diffused layer having a second conductivity type, which is formed on the light-receiving surface of the crystalline silicon substrate;

a first electrode formed on the surface of the impurity-diffused layer on the light-receiving surface of the crystalline silicon substrate;

a second electrode formed on the back surface of the crystalline silicon substrate; and

a back reflection layer formed on the back surface of the crystalline silicon substrate;

wherein said second electrode provides a contact on the back surface of the crystalline silicon substrate through a plurality of openings of the back reflection layer.

5. The method according to claim 1, wherein said solar cell comprises:

a crystalline silicon substrate having a first conductivity type, which is composed of a single crystalline silicon or a polycrystalline silicon;

an impurity-diffused layer having a second conductivity type, which is formed on the light-receiving surface of the crystalline silicon substrate;

a first electrode formed on the surface of the impurity-diffused layer on the light-receiving surface of the crystalline silicon substrate;

a second electrode formed on the back surface of the crystalline silicon substrate; and

an impurity-diffused layer having a first conductivity type, which layer is formed on a part or all of the back surface of the crystalline silicon substrate, and in which layer higher concentrations of impurities than the concentration of impurities in the crystalline silicon substrate are added; and

a back reflection layer formed on the surface of the impurity-diffused layer having a first conductivity type;

wherein said second electrode provides a contact on the surface of the impurity-diffused layer on the back surface of the crystalline silicon substrate through a plurality of openings of the back reflection layer.

6. A solar cell comprising the back reflection layer formed by the method according to claim 1.

7. The method according to claim 1, wherein said light-reflecting particles are tantalum(V) oxide (Ta₂O₅).

8. The method according to claim 1, wherein the content of said light-reflecting particles in the composition is 10 to 50% by weight.

9. The method according to claim 1, wherein said light-reflecting particles have a particle size of 0.01 to 0.3 μ

m.

10. The method according to claim 1, wherein said polyimide resin comprises recurring units represented by the following formula [I]:

11. The method according to claim 10, wherein said Ar² is represented by the following formula [III]:

12. The method according to claim 10, wherein said Ar² is represented by the following formula [IV]:

13. The method according to claim 10, wherein said Ar² is represented by the following formula [V]:

14. The method according to claim 1, wherein said polyimide resin contains 1,3-bis(3-aminopropyl)tetramethyldisiloxane in an amount of 1 to 25 mol % based on total diamine components.

15. The method according to claim 1, wherein the composition has a thixotropy coefficient of from 1.5 to 4.0.

16. The method according to claim 1, wherein the composition has a thixotropy coefficient of from 1.8 to 3.5.

17. The method according to claim 1, wherein the composition has a thixotropy coefficient of from 2.5 to 3.2.