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EP-4740711-A1 - THIN FILM SOLAR CELL AND CORRESPONDING PRODUCTION METHOD

EP4740711A1EP 4740711 A1EP4740711 A1EP 4740711A1EP-4740711-A1

Abstract

The invention relates to thin film CIGS solar cells. A method for producing such solar cell comprises the ordered steps of: providing a substrate (12); forming a back-electrode layer (14) on the substrate; forming a hole transport structure (20) on the back electrode layer, the hole transport structure comprising a hole transport layer (16) comprising p-type conductive material on the back-electrode layer and a stabilizing layer (18) on the hole transport layer, the stabilizing layer comprising a metal oxide and/or a metal nitride; and forming a semiconductor absorber layer (22) on the hole transport structure, the absorber layer comprising chalcogenide material. A corresponding thin film solar cell with such double-layer hole transport structure is also presented.

Inventors

  • WANG, Taowen
  • SONG, Longfei

Assignees

  • Université du Luxembourg

Dates

Publication Date
20260513
Application Date
20240705

Claims (20)

  1. 1 . A method for producing a thin film solar cell comprising the ordered steps of: providing a substrate (12); forming a back-electrode layer (14) on said substrate; forming a hole transport structure (20) on said back electrode layer, said hole transport structure comprising a hole transport layer (16) comprising p-type conductive material on said back-electrode layer and a stabilizing layer (18) on said hole transport layer, said stabilizing layer comprising a metal oxide and/or a metal nitride; and forming a semiconductor absorber layer (22) on said hole transport structure, said absorber layer comprising chalcogenide material.
  2. 2. The method as claimed claim 1 , wherein said stabilizing layer comprises metal oxides and/or metal nitrides of one or more metals selected from the group comprising Si, Mo, Al, Ga, In, Ti and Hf.
  3. 3. The method as claimed in claim 1 or 2, wherein said stabilizing layer is deposited as a metal oxide selected from the group comprising AI2O3, Ga2O3, ln2O3, TiO2, MoO2, and their mixtures.
  4. 4. The method as claimed in any one of claims 1 to 3, wherein the stabilizing layer has a thickness between 10 and 100 nm.
  5. 5. The method as claimed in any one of the preceding claims, wherein a conduction band minimum of the stabilizing layer is greater than that of the absorber layer, preferably by at least 0.3 eV.
  6. 6. The method as claimed in any one of the preceding claims, wherein the hole transport layer comprises p-type chalcogenide material.
  7. 7. The method as claimed in claim 6, wherein the hole transport layer comprises a material selected from the group consisting of Cu(ln,Ga)Se2, Cu(ln,Ga)(Se,S)2, CulnSe2, CuGaSe2, CulnS2, Cu(ln,Ga)S2 and their mixtures.
  8. 8. The method as claimed in any one of the preceding claims, wherein the hole transport layer has a thickness of between 30 and 200 nm.
  9. 9. The method as claimed in any one of the preceding claims, wherein the absorber layer comprises, preferably consists of, a material selected from the group consisting of Cu(ln,Ga)Se2, Cu(ln,Ga)(Se,S)2, CulnSe2, CuGaSe2, CulnS2, Cu(ln,Ga)S2 and their mixtures.
  10. 10. The method as claimed in any one of the preceding claims, wherein the absorber layer has a thickness of 0.1 to 3 pm.
  11. 11. The method as claimed in any one of the preceding claims, wherein forming said hole transport structure includes forming a copper layer (21 ) adjacent said stabilizing layer.
  12. 12. The method as claimed in claim 11 , comprising annealing the layer stack with said copper layer (21 ) on top at a temperature between 400 and 600°C, preferably between 450°C and 550°C, in particular about 500°C, for a time period between 5 and 30 min, in particular between 10 and 20 min.
  13. 13. The method as claimed in claim 11 or 12, wherein said copper layer has a thickness similar to said stabilizing layer.
  14. 14. The method as claimed in any one of the preceding claims, comprising depositing a sodium layer between the hole transport layer and the stabilizing layer.
  15. 15. The method as claimed in the preceding claim, further comprising the steps of - forming an electron transport layer above the absorber layer; and - forming a top electrode layer above the electron transport layer.
  16. 16. A thin film solar cell comprising: a substrate (12); a back-electrode layer (14) on said substrate; a hole transport structure (20) on said back-electrode layer, said hole transport structure including a hole transport layer (16) comprising p-type conductive material; a semiconductor absorber layer (22) on said hole transport structure, said absorber layer comprising chalcogenide material; an electron transport layer (24) on the semiconductor absorber layer; and a top electrode layer (26) on the electron transport layer, wherein said hole transport structure (20) further comprises a stabilizing layer (18) on said hole transport layer (16), said stabilizing layer comprising a metal oxide and/or a metal nitride.
  17. 17. The thin film solar cell as claimed in claim 16, wherein said stabilizing layer comprises metal oxides and/or metal nitrides of one or more metals selected from the group comprising Si, Mo, Al, Ga, In, Ti and Hf.
  18. 18. The thin film solar cell as claimed in claim 16 or 17, wherein the stabilizing layer has a thickness between 10 and 100 nm.
  19. 19. The thin film solar cell as claimed in any one of claims 16 to 18, wherein a conduction band minimum of the stabilizing layer is greater than that of the absorber layer, preferably by at least 0.3 eV.
  20. 20. The thin film solar cell as claimed in any one of claims 16 to 19, wherein the stabilizing layer further comprises annealed copper.

Description

THIN FILM SOLAR CELL AND CORRESPONDING PRODUCTION METHOD Technical field The invention generally relates to the field of photovoltaic devices such as solar cells and solar panels, and more particularly to thin film solar cells and methods for producing same. Background of the Invention Solar cells are one class of energy source devices which harness a renewable source of energy in the form of light that is converted into useful electrical energy which may be used for numerous applications. Thin film solar cells are multi-layered semiconductor structures formed by depositing various thin layers and films of semiconductor and other materials on a substrate. These solar cells may be made into light-weight flexible sheets in some forms comprised of a plurality of individual electrically interconnected cells. The attributes of light weight and flexibility gives thin film solar cells broad potential applicability as an electric power source for use in portable electronics, aerospace, and residential and commercial buildings where they can be incorporated into various architectural features such as roof shingles, facades, and skylights. Thin film solar cells, such as CIGS (copper indium gallium selenide) solar cells, generally comprise a back contact or electrode formed on the substrate and a top contact or electrode formed above the back electrode and electrically connected thereto. In contrast to conventional Si solar cells, thin film solar cells generally have a fully metallic back contact (or back electrode layer), that causes the loss of light generated electrons by electron-hole recombination, also known as back surface recombination. In order to improve the efficiency of the thin film solar cell, attempts have been made to limit this recombination. Document US 2015/380596 A discloses a method for producing a thin film CIGS solar cell which mitigates the back surface recombination by a compositional gradient of Gallium that increases the conduction band edge energy towards the back contact. This gradient reduces backside recombination by keeping minority carriers away from the back contact, and can greatly reduce the non-radiative loss in open-circuit voltage. However, the band gap gradient leads to various losses: (i) the zone of the minimum band gap, which determines the absorption edge, is rather thin, which leads to non-absorption losses in the short circuit current; the gradual absorption onset leads to radiative losses in the open circuit voltage; and the regions with the highest content of Gallium near the back contact have been shown to exhibit an extremely low carrier lifetime below 100ps, which can be attributed to additional deep defects in high band gap chalcopyrite. Furthermore, from a technological point of view the need for a compositional gradient makes the absorber unnecessarily thick, which increases production cost. Document CN 112786713 A discloses a method for producing a thin film CIGS solar cell which mitigates the back surface recombination by providing an additional layer between the back contact and the CIGS absorber layer. However, the additional layer is non-conductive and requires a structuration in order to transport holes, which complicates the production process and increases the production costs. Object of the invention Hence, there is a need for an improved design/manufacturing approach of thin film solar cells that does not present the above-mentioned drawbacks. This object is achieved by a thin film solar cell according to claim 1. General Description of the Invention According to the present invention a method for producing a thin film solar cell comprises the ordered steps of: providing a substrate; forming a back-electrode layer on the substrate layer; forming a hole transport structure on the back-electrode layer; forming a semiconductor absorber layer on said hole transport structure, the absorber layer comprising chalcogenide material; wherein the hole transport structure comprises a hole transport layer with p-type conductive material on the back-electrode layer and a stabilizing layer on the hole transport layer, the stabilizing layer comprising a metal oxide and/or a metal nitride. In other words, the step of forming a hole transport structure on the back electrode comprises a step of forming a hole transport layer comprising p-type conductive material on the back electrode layer, and a (subsequent) step of forming a stabilizing layer on the hole transport layer. Here, the hole transport layer is preferably directly formed on the back electrode layer and then stabilizing layer is directly formed on the hole transport layer. Preferably at least one, and more preferably both of, the hole transport layer and the stabilizing layer is a continuous layer, meaning fully cover the underlying layer without openings. This advantageously simplifies the fabrication process and ensures good performances (e.g. in terms of fill factor and/or open circuit voltage) of the hole