Cu(In,Ga)(Se,Te)2 pentenary thin films formed by reaction of precursor layers

Abstract

Sodium doped CuIn(1−x)Gax(Se(1−y)Tey)2 (CIGST) thin films were grown on Mo-coated soda lime glass substrates by a two-stage technique. The effects of Te content and annealing temperature on the microstructural characteristics and phase segregation in CIGST thin films were studied. It was observed that presence of Ga in these films affected the kinetics of the reaction and phase formation and largely eliminated the separation of the Te-rich phase towards the Mo surface, which was previously observed under the two-stage processing conditions in films containing only Cu, In, Se and Te. Microprobe measurements showed that the smaller grain material visible through the gaps within the larger grain material had higher Ga and Se content compared to larger grains, which were richer in Te and In. For CIGS film formation, an annealing regime that involved a low temperature partial reaction step followed by a high temperature reaction step yielded better films compared to a process with a single high temperature step. However, for films containing both Se and Te, the two temperature processing approach caused excessive phase separation.