Electrochemical synthesis of Cu2ZnSnS4 and Cu2ZnSnSe4 thin films for solar cells

Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) thin films were fabricated by successive electrodeposition of layers of precursor elements followed by sulfurization and selenization of an electrodeposited Cu-Zn-Sn-Se precursor. It is known that the Sn layer tends to have an island-shaped morphology, leading to formation of inhomogeneous CZTS films with rough surface. In order to improve qualities of the CZTS film, we tried to optimize the deposition condition of Sn layers. As a result, we were able to deposit Sn layers with improved morphologies. A CZTS solar cell fabricated using the Sn layer showed energy conversion efficiency of 4.4%. We also fabricated CZTSe films using Cu-Zn-Sn-Se films made by one-step electrochemical deposition as the precursor films. These films were converted into CZTS films by anneling in Ar. However, the annealing induced significant losses of Sn and Se components. These losses could be suppressed by introduction of Se vapor into the Ar atmosphere. The solar cells based on CZTSe films prepared by these methods exhibited appreciable properties.