Towards phase pure kesterite CZTS films via Cu-Zn-Sn electrodeposition followed by sulfurization

Electrodeposition of Cu-Zn-Sn alloy precursors followed by sulfurization has been utilized to form phase pure CZTS absorber layers for photovoltaic applications. In this study, we have varied the deposition potential in order to grow Cu-Zn-Sn metallic precursor layers with a fixed Cu fraction while varying the Zn/Sn ratio within the ideal composition range to obtain high quality CZTS films. The phase purity and crystal quality of CZTS films were investigated as a function of Zn/Sn ratio. Phase purity and photoelectrochemical response are both enhanced with increasing Zn/Sn ratio after sulfurization at 500 °C or 550 °C. The highest photoelectrochemical response at a liquid junction is 0.99 mA/cm² for CZTS layer with Zn/Sn = 0.98 after sulfurization at 550 °C. Raman spectroscopy and X-ray diffraction studies suggest that the enhanced photoresponse is correlated to a high crystallinity together with improved phase purity.