Thermal Annealing-Free SnO₂ for Fully Room-Temperature-Processed Perovskite Solar Cells

The SnO₂ electron transport layer (ETL) for perovskite solar cells (PSCs) has been recognized as one of the most reported protocols due to its processing convenience, high reproducibility, and excellence in device performance. To date, the thermal annealing (TA) process is still an essential step for a high-quality SnO₂ ETL to reduce the surface trap density. This however could restrict its processing with high thermal energy input and set a barrier to the easiness of manufacturing such as processing under room-temperature conditions. Herein, we report a thermal annealing-free (TAF) SnO₂ ETL by an alternative UV-ozone (UVO) treatment. This technique simultaneously endows the SnO₂ ETL with a deeper valence band maximum (E_VB) and lower defect density. Furthermore, with this SnO₂ ETL, a power conversion efficiency (PCE) of 21.46 and 22.26% was achieved based on MAPbI₃ and Cs_0.05(FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃ absorbers, respectively. Importantly, a fully room-temperature-processed (RTP) PSC based on the TAF-SnO₂ ETL has been demonstrated with a PCE of 20.88% on a rigid substrate and 15.92% on a flexible substrate, which are the highest values for RTP solar cells.