Effect of composition gradient in Cu(In,Al)Se2 solar cells

Hayashi, Takao, Minemoto, Takashi, Zoppi, Guillaume, Forbes, Ian, Tanaka, Kenji, Yamada, Satoshi, Araki, Tsutomu and Takakura, Hideyuki (2009) Effect of composition gradient in Cu(In,Al)Se2 solar cells. Solar Energy Materials and Solar Cells, 93 (6-7). pp. 922-925. ISSN 0927-0248

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Abstract

Cu(In,Al)Se2 (CIAS) thin films were prepared by a three-stage evaporation process. In this experiment, the composition ratio of Cu/(In+Al) at the end of the second stage (Cu/III2nd) was changed from 1.1 to 1.7. The CIAS films showed an Al distribution with a V-shape profile. The valley depth of the V-shape from the surface increased with increasing the Cu/III2nd ratio. The valleys of the V-shape for the films with the Cu/III2nd ratio of 1.1–1.7 were located at approximately 0.3–1.0 ?m from the film surface, respectively. The rms surface roughness increased from 40 nm for Cu/III2nd=1.1 to 90 nm at Cu/III2nd=1.3 and then saturated for greater Cu/III2nd ratios. Solar cells with the Al/ITO/ZnO/CdS/CIAS/Mo/soda-lime glass structure were fabricated. The fill factor was seen to decrease while the product of short-circuit current and open-circuit voltage remained constant. The reverse saturation current increased when the Cu/III2nd ratio is greater than 1.3 which is a behavior of the surface roughness. Cu/III2nd ratios greater than 1.3 lead to the distant position of V-shape from the surface and the increase in surface roughness.

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