Bismuth-doped Cu(In,Ga)Se2 solar cell on flexible stainless steel substrate: Examination of bismuth-doping effectiveness under different substrate temperatures on photovoltaic performances

Abstract

Bismuth (Bi)-doped flexible Cu(In,Ga)Se2 (CIGS) films on stainless steel (SUS) substrates with different Bi contents are prepared, obtained by covering Bi thin layers (as Bi source) on Mo layers with Bi thickness from 0 (without Bi-doping) to 100 nm. It is disclosed that [Ga]/([Ga] + [In]) profiles are almost identical when Bi content is increased by enhancing the Bi thickness. The CIGS grain size and carrier lifetimes are improved through the proper Bi-doping (Bi thickness of 20–65 nm) under low deposition temperature of 457 °C. The 12.6%-efficient flexible Bi-doped CIGS solar cell under the deposition temperature of 457 °C is consequently obtained. Conversion efficiency of the flexible Bi-doped CIGS solar cell under the low deposition temperature of 486 °C is further enhanced to 14.8%, very close to that (15.1%) of the solar cell under convention deposition temperature (543 °C) without Bi-doping. Furthermore, the Bi-doping is effective for the enhancement of the photovoltaic performances under the deposition temperature range of 457–486 °C, whereas the Bi-doping under high CIGS deposition temperature range of 543–572 °C has the detrimental impact on the cell parameters, resulting from the sever Bi diffusion into the CIGS film.