Co-electrodeposited Cu2ZnSnS4 thin-film solar cells with over 7% efficiency fabricated via fine-tuning of the Zn content in absorber layers

Abstract

A simple and cost-effective co-electrodeposition process has been demonstrated to fabricate high-performance Cu₂ZnSnS₄ (CZTS) photovoltaic materials with composition tunability and phase controllability. Here we report a systematic investigation of the effects of the Zn(II) concentration on the properties of CZTS thin films and thus the performance of the as-resulted solar cells. These results indicate that increasing the concentration of Zn(II) linearly increases the Zn content in the final composition of CZTS thin films, significantly improves the grain size and morphology of the absorber layers, and consequently improves their photovoltaic properties, especially the response to the medium wavelength. In contrast, further increase of the Zn(II) concentration degrades the crystal quality of the absorber layer, and more ZnS phase appears on the surface of the CZTS thin film, forming a rather rough morphology, which is harmful to the photovoltaic performance of the device. When the concentration of Zn(II) is optimized to 30 mM, a power conversion efficiency of 7.23% is achieved, which, to the best of our knowledge, is the highest efficiency for a co-electrodeposited CZTS solar cell with a sputtered CdS buffer layer to date. Our findings offer a promising alternative approach towards the industrialization of CZTS solar cell modules.