Energy band alignment for Cd-free antimony triselenide substrate structured solar cells by Co-sputtering ZnSnO buffer layer

Antimony selenide (Sb2Se3) have developed as an environmental-friendly photoactive materials for low-cost photovoltaics due to its non-toxic elements and excellent optoelectronic properties. However, chemical bath deposited (CBD) CdS thin film was generally employed as electron transport layer (ETL) in substrate or superstrate structured Sb2Se3 solar cells, which was still a huge concern restraining its long-term advancement. In this work, we have replaced the toxic CdS film by employing ZnSnO films fabricated through magnetron co-sputtering technique to develop Cd-free ZnSnO/Sb2Se3 solar cells. It was observed that Sn/(Zn + Sn) in ZnSnO film affecting the energy band alignment with Sb2Se3 take part in improving the device efficiency. Substrate structured Cd-free Sb2Se3 based devices with a champion device performance of 3.44%, were firstly made with the optimized Zn0.57Sn0.43O buffer layer closely related to the rational band alignment, the reduced recombination losses at interface (ZnSnO/Sb2Se3), and efficient charge transfer. This substituted sputtering ZnSnO for CBD-CdS film demonstrated remarkable potential to efficient and Cd-free Sb2Se3 solar cell with full-vacuum process.