Light-Assisted Electrochemical Shunt Passivation for Photovoltaic Devices

• US 20070256729A1
• Filed: 04/15/2005
• Published: 11/08/2007
• Est. Priority Date: 04/16/2004
• Status: Abandoned Application

• Current Assignee: University of Toledo
• Original Assignee: University of Toledo
• Inventors: Deng, Xunming, Vijh, Aarohi
• Application Number:
  US11/578,359
• Publication Number:
  US 20070256729A1
• Time in Patent Office: Days
• US Class Current: 136/252
• CPC Class Codes: H01L 31/076 Multiple junction or tandem solar cells
• CPC Class Codes: H01L 31/208 Particular post-treatment of the devices, e.g. annealing, short-circuit elimination
• 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
• CPC Class Codes: Y10T 29/53135 Storage cell or battery

Abstract

A method of passivating current-shunting defects in a photovoltaic device and such passivated photovoltaic devices are described. The photovoltaic device includes a thin film body with a superposed electrode comprised of a layer of transparent electrically conductive electrode material. The method includes converting the transparent, electrically conductive electrode material to a material having a higher electrical resistivity than the transparent electrically conductive electrode material or by removing the transparent conducting electrode material, by simultaneously: 1) immersing at least a portion of the electrode in a conversion reagent, 2) illuminating the immersed electrode with a suitable source of illumination, and 3) applying an appropriate electrical bias to activate the conversion.

Claims

1. A method of passivating any performance-reducing shunting defects in a photovoltaic cell having one or more layers of a thin film semiconductor material and layer of a superposed electrode, the method comprising:

immersing at least a portion of the photovoltaic cell in a conversion reagent,

illuminating at least a portion of the immersed photovoltaic cell with a suitable source of illumination, and

applying an appropriate electrical bias voltage on the immersed photovoltaic cell.

2. The method of claim 1, comprising using an electrolyte which increases the resistivity of the electrode near the performance reducing shunt when the electrical bias voltage is applied in a preferred range, while the change in resistivity is substantially smaller outside of the bias voltage range.

3. The method of claim 2, comprising illuminating with a light of a wavelength which activates the thin film semiconductor layer and causes production of a photovoltage.

4. The method of claim 3, comprising illuminating light with a suitable wavelength and a sufficient intensity whereby the photovoltage produced by the illumination in an unshunted region inhibits the increase of the resistivity of the electrode material in the unshunted regions.

5. The method of claim 4, wherein the electrode is a transparent and electrically conductive material which is superposed on an illumination side of the semiconducting layer.

6. The method of claim 5, wherein the transparent, electrically conducting material comprises indium-tin oxide (ITO), indium oxide, tin oxide and other doped or alloyed variations of these oxide materials.

7. The method of claim 6, wherein the thin film semiconductor layers for the photovoltaic device comprise at least one of amorphous silicon, amorphous germanium, microcrystalline silicon, nanocrystalline silicon or their alloys.

8. The method of claim 1, wherein the electrolyte comprises an aqueous solution of aluminum chloride (AlCl₃).

9. The method of claim 7, wherein the photovoltaic device comprises a triple junction solar cell comprising at least one of amorphous silicon, amorphous germanium, microcrystalline silicon, nanocrystalline silicon or their alloys.

10. The method of claim 4, wherein the electrode is on a backside of the semiconductor layers, opposite to an illumination-entering side.

11. The method of claim 10, wherein the semiconductor layers are illuminated from the illumination-entering side during the passivation process.

12. The method of claim 11, wherein the electrode comprises at least one of a transparent oxide layer or a thin metal layer.

13. The method of claim 4, wherein the surface of the electrode is partially or fully illuminated without restricting the illumination to only the shunted regions or near the shunted regions.

14. The method of claim 1, wherein a front surface of the photovoltaic cell is illuminated by a tungsten halogen lamp, and wherein the electrical bias of from approximately 1 to approximately 4 volts is applied between the counter-electrode which comprises an aluminum mesh that allows the passage of light, and steel electrode for a suitable period of time of from approximately 1 to approximately 30 seconds and electrolyte conductivity of from approximately 0.2 to approximately 100 mS/cm.

15. The method of claim 4, wherein a front surface of the photovoltaic cell is illuminated by a tungsten halogen lamp, and wherein an electrical bias of from approximately 1 to approximately 4 volts is applied between the counter-electrode which comprises an aluminum mesh that allows the passage of light, and steel electrode for a suitable period of time of 1-30 s and electrolyte conductivity of from approximately 0.2 to approximately 100 mS/cm.

16. The method of claim 4, wherein the passivation is carried out in two or more steps, each step having different passivation conditions which are optimal for shunts having different shunt resistances.

17. The method of claim 16, wherein the passivation is carried out in two steps, each step employing a different voltage bias.

18. The method of claim 17, wherein the first passivation step is carried out with a first bias voltage and the second passivation step is carried out with a second bias voltage, wherein the first voltage is smaller than the second voltage.

19. The method of claim 4, wherein the bias voltage is changed smoothly during shunt passivation.

24. A photovoltaic device made using the method of the claim 1.

25. A photovoltaic device made using the apparatus of the claim 1.

20. An apparatus for performing the light-assisted shunt passivation in a photovoltaic cell, the apparatus comprising:

an electrolyte, a counter-electrode, and a conducting electrode placed in near or in contact with the photovoltaic cell.

21. The apparatus of claim 20, further including a source of illumination positioned in opposing relationship to the conducting electrode.

22. The apparatus of claim 21, wherein the illumination source comprises wavelengths which activate the thin film semiconductor layers.

23. The apparatus of claim 20, further including a voltage ramp for substantially smoothly changing the bias voltage during shunt passivation.