Anti-solvent spin-coating for improving morphology of lead-free (CH3NH3)3Bi2I9 perovskite films

Methylammonium iodide bismuthate ((CH3NH3)3Bi2I9) (MIB) perovskite has attracted research attention because of its low toxicity and stability in air. However, MIB perovskite also has its inherent defects, e.g., MIB films have too many pinholes and large indirect band gap. Our group has also done some efforts to successfully improve the performance of MIB-based PSC. One of the recent works focused on the use of diethyl ether (DEE) as anti-solvent to improve film compactness and reduce pinhole defects. The characterization indicated that the films treated by DEE (DEE/MIB) were compact with fewer pinholes. The devices fabricated with DEE/MIB based on mesoporous TiO2 (mp-TiO2) architecture exhibited good performance in terms of Voc (885 mV), Jsc (0.807 mA cm−2), and FF (49.71%), with a power conversion efficiency of 0.343%, which were much higher than that of the contrast test and results of our previous work. The present devices also exhibited superior long-term stability in ambient air (approximately 30% humidity) of more than 200 days.