23 February 2017 Device physics of Cu(In,Ga)Se2 solar cells for long-term operation
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Abstract
The degradation mechanism of Cu(In,Ga)Se2 (CIGS) solar cells on exposure to air has been investigated. Exposure to air at room temperature slightly reduces the conversion efficiency of CIGS solar cells, and the conversion efficiency decreases significantly under damp heat testing at 85 °C and 85% relative humidity due to low shunt resistance. On the other hand, shunt resistance increases after dry nitrogen heating. Therefore, oxygen and humidity should degenerate the solar cell performance. The low shunt resistance and conversion efficiency are completely recovered after removing the side edges of the CIGS solar cells by mechanical scribing. These results suggest that low-resistive layers are formed on the sidewalls of the solar cells during damp heat testing. The low-resistive layers on the sidewalls are identified to be molybdenum oxides and sodium molybdate by Auger electron spectroscopy. After etching the oxides on the sidewalls by alkaline solution, the saturation current density and ideality factor are confirmed to be improved. These results suggest that metal oxides on the sidewalls of CIGS solar cells may act as recombination centers.
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J. Nishinaga, H. Shibata, "Device physics of Cu(In,Ga)Se2 solar cells for long-term operation", Proc. SPIE 10099, Physics, Simulation, and Photonic Engineering of Photovoltaic Devices VI, 100990B (23 February 2017); doi: 10.1117/12.2253807; https://doi.org/10.1117/12.2253807
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