HI-assisted fabrication of Sn-doping TiO₂ electron transfer layer for air-processed perovskite solar cells with high efficiency and stability

Effective electron transport layers (ETLs) provide enhanced charge separation and transport, therefore as a vital part in improving the efficiency of planar perovskite solar cells (PSCs). Herein, we report a new synergistic strategy using HI to passivate TiO₂ film and surface while incorporating tin element into TiO₂ ETL. HI is first used to control the hydrolysis of TiO₂ precursors and eliminate oxygen vacancies related trap states. Then, tin element is incorporated into HI-passivated TiO₂ precursor solution to construct composite TiO₂/SnO₂ film, affording increased electron mobility and suitable energy level. Moreover, the entire preparation process is performed under uncontrolled environmental conditions at 150 °C temperatures. Benefiting from the improved quality of the ETLs, the unencapsulated PSCs achieve optimized power conversion efficiency (PCE) of 17.77% with greatly improved stability. After storage in ambient for 1450 h, the device still maintains 92% of its initial efficiency, while hold 79% PCE after 7 h of 1 sun exposure and 86% PCE after heating at 100 °C for 21 h.