“…In addition to this properties, this material has an advantage on the environmental pollution issue since it is chemically stable and has no highly toxic elements composed in it. However, the researches concerning with this CTGS alloy in the thin-film photovoltaic applications are still in the early initial phase and the study on CTGS alloy itself with various Ge contents is still premature compared to the study of individual Cu 2 SnS 3 (CTS) or Cu 2 GeS 3 (CGS) ternary compounds [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32]. Up to now, only a few reports about the photovoltaic devices based on the CTGS with various Ge contents have been made [12,33,34].…”