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 degrees 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 degrees C for 21 h.