Formation of intermediate solid solutions in the quaternary exchange system Cu(In,Ga)(S,Se)2–2Cd(S,Se)

Abstract

While record solar cells based on Cu(In,Ga)Se2 (CIGS) absorbers exhibit the highest conversion efficiencies among all thin film photovoltaic technologies, the structural nature of the electronically favourable heterojunction CIGS–CdS is still debatable. Here, we present an investigation of the phase equilibria in the full Cu(In,Ga)(S,Se)2–2Cd(S,Se) quaternary exchange system at the selected annealing temperature of 870 K in order to reveal the formation of intermediate solid solutions. There are three single phase regions in the system: the chalcopyrite α-solid solution based on Cu(In,Ga)(S,Se)2, the wurtzite β-solid solution of Cd(S,Se), and the intermediate γ-solid solution existing in a zinc blende structure. The γ-phase has a broad homogeneity range and crystallizes in the cubic space group F3m with a statistical distribution of metal atoms in the cation sub-lattice.