Epitaxial Cu2ZnSnSe4 thin films and devices

Epitaxial Cu2ZnSnSe4 (CZTSe) thin films have been grown via high temperature coevaporation on GaAs(001). Electron backscattering diffraction confirms epitaxy in a wide compositional range. Different secondary phases are present in the epitaxial layer. The main secondary phases are Cu2SnSe3 and ZnSe which grow epitaxially on top of the CZTSe. Transmission electron microscopy measurements show that the epitaxial CZTSe grows predominantly parallel to the c-direction. Epitaxial CZTSe solar cells with a maximum power conversion efficiency of 2.1%, an open-circuit voltage of 223 mV and a current density of 16 mA/cm2 are presented.