Effect of Sn content in a CuSnZn metal precursor on formation of MoSe₂ film during selenization in Se+SnSe vapor

The preparation of Cu₂ZnSnSe₄ (CZTSe) thin films by the selenization of an electrodeposited copper-tin-zinc (CuSnZn) precursor with various Sn contents in low-pressure Se+SnSe_x vapor was studied. Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) measurements revealed that the Sn content of the precursor that is used in selenization in a low-pressure Se+SnSe_x vapor atmosphere only slightly affects the elemental composition of the formed CZTSe films. However, the Sn content of the precursor significantly affects the grain size and surface morphology of CZTSe films. A metal precursor with a very Sn-poor composition produces CZTSe films with large grains and a rough surface, while a metal precursor with a very Sn-rich composition procures CZTSe films with small grains and a compact surface. X-ray diffraction (XRD) and SEM revealed that the metal precursor with a Sn-rich composition can grow a thicker MoSe₂ thin film at CZTSe/Mo interface than one with a Sn-poor composition, possibly because excess Sn in the precursor may catalyze the formation of MoSe₂ thin film. A CZTSe solar cell with an efficiency of 7.94%was realized by using an electrodeposited metal precursor with a Sn/Cu ratio of 0.5 in selenization in a low-pressure Se+SnSe_x vapor.