Surface modifications of CIGS absorbers and their effects on performances of CIGS solar cells

Abstract The surface roughness of CIGS absorber and residual Cu–Se phase on the surface are two major factors greatly affecting the performance of CuInGaSe2 (CIGS) solar cells with the absorbers fabricated by the selenization annealing of Cu–In-Ga precursors. In this work, Br2–CH3OH solution is used to etch the surfaces of CIGS films to address these two challenges. The effects of the etching treatment on CIGS films and devices are investigated. It is found that etching significantly reduces the film roughness and removes the Cu–Se phase. Thus, the performance of the device is improved within a certain range. In addition, it is found that CIGS films with suitable surface roughness effectively absorb incident light and possess a higher Jsc. However, excessive etching causes the film to be too thin, and the carrier recombination at the back electrode increases. Based on these characteristics, this work optimizes the Br2 etching process.