Hydrothermally-assisted selenization of CuInSe2 thin films on copper foils

CuInSe2 films were successfully prepared on copper foils via the hydrothermally-assisted selenization process. The selenization temperature was decreased significantly to as low as 220 °C using triethanolamine as the chelating agent. Without adding the chelating agent, only the Cu2−xSe phase was observed, whereas chalcopyrite was formed with triethanolamine added as the chelating agent. As the hydrothermal temperatures were increased and the heating duration was prolonged, single-phased dense CuInSe2 films were formed. The chemical composition profiles versus depth indicated the amount of indium ions decreased with the increase of the detection time. GIXD and SIMS results indicated that the diffusion of indium ions facilitated the formation of CuInSe2 onto copper foils. According to the experimental results, the following hydrothermally-assisted selenization process is proposed: selenium ions first react with copper foils to form Cu2−xSe at low temperatures, then indium ions and selenium ions react to form In2Se3 on the Cu2−xSe surface, finally Cu2−xSe and In2Se3 react with each other to yield CuInSe2.