Solution-processed Cu₂ZnSnS₄ thin film with mixed solvent and its application in superstrate structure solar cells

Cu₂ZnSnS₄ (CZTS) thin film solar cells become an interesting research topic due to some advantages of the CZTS thin film such as having nontoxic and abundant components, a low price and excellent optoelectronic properties. In this work, a solution-based preparation method was developed to fabricate a CZTS solar cell with a superstrate structure of FTO/TiO₂/CdS/CZTS/P3HT/Cu by using mixed solvent. Nanocrystalline TiO₂ porous thin film was used as the bottom layer for deposition of CZTS to increase the interfacial area of CZTS. To deposit CZTS inside the porous structure leading to a good contact of CZTS with porous TiO₂ thin film, the CZTS precursor particle size is successfully regulated by changing the volume ratios of N,N-dimethylformamide and ethanol. More importantly, small size CZTS precursor particles can easily enter into the porous structure of nanocrystalline thin film leading to a good interfacial contact, which allowed the effective improvement of the light-to-electric conversion efficiency for the present superstrate CZTS solar cell. This work may provide a promising way for the design of high-efficient superstrate solar cells.