CO2 Plasma-Treated TiO2 Film as an Effective Electron Transport Layer for High-Performance Planar Perovskite Solar Cells

Perovskite solar cells (PSCs) have received great attention because of their excellent photovoltaic properties especially for the comparable efficiency to silicon solar cells. The electron transport layer (ETL) is regarded as a crucial medium in transporting electrons and blocking holes for PSCs. In this study, CO2 plasma generated by plasma-enhanced chemical vapor deposition (PECVD) was introduced to modify the TiO2 ETL. The results indicated that the CO2 plasma-treated compact TiO2 layer exhibited better surface hydrophilicity, higher conductivity, and lower bulk defect state density in comparison with the pristine TiO2 film. The quality of the stoichiometric TiO2 structure was improved, and the concentration of oxygen-deficiency-induced defect sites was reduced significantly after CO2 plasma treatment for 90 s. The PSCs with the TiO2 film treated by CO2 plasma for 90 s exhibited simultaneously improved short-circuit current (JSC) and fill factor. As a result, the PSC-based TiO2 ETL with CO2 plasma treatment affords a power conversion efficiency of 15.39%, outperforming that based on pristine TiO2 (13.54%). These results indicate that the plasma treatment by the PECVD method is an effective approach to modify the ETL for high-performance planar PSCs.