Front electrode with thin metal film layer and high work-function buffer layer for use in photovoltaic device and method of making same

• US 20080105299A1
• Filed: 11/02/2006
• Published: 05/08/2008
• Est. Priority Date: 11/02/2006
• Status: Abandoned Application

• Current Assignee: Guardian Glass LLC (KOCH Industries Incorporated)
• Original Assignee: Guardian Industries Corporation (KOCH Industries Incorporated)
• Inventors: Krasnov, Alexey
• Application Number:
  US11/591,676
• Publication Number:
  US 20080105299A1
• Time in Patent Office: Days
• US Class Current: 136/256
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/022466 made of transparent conductive layers, e.g. TCO, ITO layers
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

This invention relates to a front electrode or contact for use in an electronic device such as a photovoltaic device. In certain example embodiments, the front electrode of the photovoltaic device includes a highly conductive metal film and a thin high work-function buffer layer. The high-work function buffer layer is located between the metal film and the uppermost semiconductor layer so as to provide for substantial work-function matching between the metal film and the high work-function uppermost semiconductor layer so as to reduce a potential barrier for holes extracted from the device by the front electrode/contact. Optionally, a layer such as a transparent conductive oxide (TCO) or a dielectric may be provided between a front glass substrate and the metal film.

Claims

1. A photovoltaic device comprising:

a front glass substrate;

an active semiconductor film;

an electrically conductive and substantially transparent front electrode structure located between at least the front glass substrate and the semiconductor film;

wherein the front electrode structure comprises a substantially transparent metal film, and a high work function buffer film; and

wherein the high work function buffer film has a work-function that is higher than a work-function of the metal film, and the high work function buffer film is located between the metal film and an uppermost portion of the semiconductor film.

2. The photovoltaic device of claim 1, wherein the high work function buffer film comprises a TCO film.

3. The photovoltaic device of claim 1, wherein the high work function buffer film comprises indium tin oxide.

4. The photovoltaic device of claim 1, wherein the high work function film comprises oxygen-rich indium-tin-oxide (ITO).

5. The photovoltaic device of claim 1, wherein the metal film comprises first and second substantially metallic layers made of different metals.

6. The photovoltaic device of claim 1, wherein the high work function buffer film directly contacts each of the metal film and the semiconductor film.

7. The photovoltaic device of claim 1, wherein the metal film has a work-function of no greater than about 4.2 eV, and the high work function buffer film has a work function of at least 4.3 eV.

8. The photovoltaic device of claim 1, wherein the high work function buffer film has a work function of at least about 4% higher than that of the metal film, more preferably at least 6% higher, and most preferably at least about 10% higher.

9. The photovoltaic device of claim 1, wherein the high work function buffer film has a work-function of from about 4.0 to 5.7 eV.

10. The photovoltaic device of claim 1, wherein the high work function buffer film has a work-function of from about 4.3 to 5.2 eV.

11. The photovoltaic device of claim 1, wherein the high work function buffer film has a work-function of from about 4.5 to 5.0 eV.

12. The photovoltaic device of claim 1, wherein the metal film comprises one or more of Cu, Ag, Au, Al, Ni and/or Pd.

13. The photovoltaic device of claim 1, wherein the metal film comprises a first layer consisting essentially of a first metal(s), and a second layer consisting essentially of a different second metal(s).

14. The photovoltaic device of claim 1, wherein the metal film is from about 20-600 angstroms thick, and the high work function buffer film is from about 10 to 1,000 angstroms thick.

15. The photovoltaic device of claim 1, wherein the metal film is from about 40-200 angstroms thick, and the high work function buffer film is from about 10 to 100 angstroms thick.

16. The photovoltaic device of claim 1, further comprising a nucleation film located between the front glass substrate and the metal film.

17. The photovoltaic device of claim 16, wherein the nucleation film comprises a transparent conductive oxide.

18. The photovoltaic device of claim 1, wherein the high work function buffer film is a dielectric film.

19. The photovoltaic device of claim 1, wherein the high work function buffer film is a dielectric and has a thickness of from about 5-30 angstroms.

20. The photovoltaic device of claim 1, wherein the semiconductor film comprises hydrogenated amorphous silicon.

21. The photovoltaic device of claim 1, further comprising a back electrode, wherein the active semiconductor film is provided between at least the front electrode and the back electrode.

22. The photovoltaic device of claim 1, wherein the high work function barrier film is oxidation graded, continuously or discontinuously, so as to have a higher oxygen content adjacent the semiconductor film than adjacent the metal film.

23. An electrode structure adapted for use in a photovoltaic device, the electrode structure comprising:

a glass substrate;

a substantially transparent metal film supported by the glass substrate;

a high work function buffer film supported by the glass substrate, wherein the high work function buffer film has a work-function that is higher than a work-function of the metal film, and the metal film is located between at least the high work function buffer film and the glass substrate.

24. The electrode structure of claim 23, wherein the high work function buffer film comprises a TCO film.

25. The electrode structure of claim 23, wherein the metal film comprises first and second different substantially metallic layers.

26. The electrode structure of claim 23, wherein the high work function buffer film directly contacts the metal film and is also adapted to directly contact a semiconductor film of the photovoltaic device.

27. The electrode structure of claim 23, wherein the metal film has a work-function of no greater than about 4.2 eV, and the high work function buffer film has a work function of at least 4.3 eV, and wherein the high work function buffer film has a work function of at least about 4% higher than that of the metal film.

28. The electrode structure of claim 23, wherein the metal film is from about 40-200 angstroms thick, and the high work function buffer film is from about 10 to 100 angstroms thick.

29. The electrode structure of claim 23, further comprising a nucleation film located between the glass substrate and the metal film, wherein the nucleation film comprises a metal oxide.

30. The electrode structure of claim 23, wherein the high work function buffer film is a dielectric film and has a thickness of from about 5-30 angstroms.