An oxide route to preparing Cu2ZnSnSe4 thin film solar cells based on monoethanolamine-ethanol solution and two-step drying process

At present, most reported solution-processed highly efficient Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cells are prepared from precursor solutions with sulfur-containing complexing agents. However, the organic solutions with sulfur-containing groups are generally toxic and always produce harmful gases during pyrolysis. From the view of environment protection and process safety, preparing CZTSSe from the oxide precursor is more favorable for the application and development of CZTSSe photovoltaic technology compared with the sulfide precursor route. In this work, we developed a sulfur-free solution method for preparing CZTSe solar cells based on a monoethanolamine-ethanol blend wherein the ethanolamine serves as both complexing agent and reducing agent. The precursor thin film prepared is mainly composed of amorphous oxides and a small amount of copper. We found that the content of ethanolamine not only affects the formation of copper-rich phase on the surface of the precursor film, but also affects the formation of zinc-rich phase on the surface of the absorber layer. By systematically investigating the effects of ethanolamine content on precursors, absorbers and solar cells, an oxide precursor route to preparing CZTSe solar cells based on solution with low ethanolamine content and two-step drying process was successfully proposed.