Electrochemical Reduction and Ion Injection of Annealing-Free SnO₂ for High Performance Perovskite Solar Cells

The electron transport layer (ETL) plays a crucial role for efficiency and stability of perovskite solar cells (PSCs). As a promising low-temperature ETL, tin oxide still requires complicated surface chemical decoration or heat-treatments to further passivate the defects and adjust band energy level to improve the optoelectronic performance of the device. Herein, a novel and efficient strategy is developed for the solution prepared annealing-free SnO2 ETL for PSCs. Through simple electrochemical regulation, the elemental composition, valence ratio of Sn, concentration of oxygen vacancies, hydroxyl groups, and dopant ions are precisely modified with the optimized the energy band, reduce the defect density, and enhance high carrier transport for PSCs. Thus, an increase of power conversion efficiency (PCE) from 21.6% to 24.7% and a high V-OC of 1.19 V is obtained. The modified devices maintain 95% of the initial PCE after 2000 h of storage, and 80% of the initial PCE after 900 h of aging in an atmospheric environment at 75 degrees C and RH 20 +/- 5%. Moreover, the perovskite solar module based on the as made SnO2 achieve a high PCE of 21.3%.