Indium-Gallium Segregation inCuInxGa1−xSe2: AnAb Initio–Based Monte Carlo Study

Abstract

Thin-film solar cells with ${\mathrm{CuIn}}_x{\mathrm{Ga}}_{1-x}{\mathrm{Se}}_2$ (CIGS) absorber are still far below their efficiency limit, although lab cells already reach 20.1%. One important aspect is the homogeneity of the alloy. Large-scale simulations combining Monte Carlo and density functional calculations show that two phases coexist in thermal equilibrium below room temperature. Only at higher temperatures, CIGS becomes more and more a homogeneous alloy. A larger degree of inhomogeneity for Ga-rich CIGS persists over a wide temperature range, which contributes to the observed low efficiency of Ga-rich CIGS solar cells.