Characterizations of electrodeposited CuInSe 2 thin films: Structure, deposition and formation mechanisms

Abstract

Effects of annealing conditions on the structure characteristics of electrodeposited CuInSe 2 thin films were investigated by using X-ray diffractometry. For copper-rich thin films, the preferred orientation factor f(112) at (112) direction and the effective grain size increased as the annealing temperature and time increased. Less profound effects were observed for the indium-rich films. The annealed copper- rich films are predominantly chalcopyrite and highly conductive, while annealed indium-rich films are mainly sphalerite and very resistive. A structural transition from chalcopyrite to sphalerite was observed for the first time on the electrodeposited CuInSe 2 as the composition of the thin films varied from copper rich to indium rich. The presence of oxygen during annealing was found detrimental to the films, resulting in the formation of indium oxides due to partial oxidation of indium and associated loss of selenium and a large increase in the film conductivity. Effects of various chemical treatments on film composition, morphology, and corresponding structural change were also studied to elucidate the thin film deposition and formation mechanisms. The results showed that the as-deposited films are made of CuInSe 2, Cu x Se, In y Se, and seledium. Depending on the sequence of annealing and chemical treatments, the resulting thin films could be either copper- rich chalcopyrites or indium-rich sphalerites.