Summary History and current status of Cu-ternary-based photovoltaic devices are reviewed. Heterojunction and homojunction research on CuInS₂, CuInSe₂ and CuInTe₂ is covered. Some emphasis is placed on the CdS, Cd(Zn)S/CuInSe₂ thin-film solar cell, which has reached a 10% solar-conversion efficiency and has demonstrated remarkable stability characteristics. Fundamental properties of interface formation are presented, by using surface analysis (AES, angular-resolved XPS, EELS) techniques. The possible formation of binary semiconductor compounds (e.g. Cu _x S and Cu _x Se) during the initial stages of heterojunction formation is reported. The evaluation of heterojunction response is studied by using high-resolution electron-beam-induced current (EBIC) investigations on fractured solar-cell cross-sections. Schottky barrier and homojunction responses are reported for present solar-cell designs. The importance and effects of postdeposition heat treatments on the performance of these thin-film cells are discussed. In particular, complementary EBIC and SIMS data are used to ascertain the necessity of the oxygen/temperature treatments of this device. learn more