Efficient inorganic perovskite solar cells made by drop-coating in ambient air

Inorganic perovskites are receiving growing attention due to good thermal stability and fast-improving photovoltaic performance. However, most of the high-efficiency inorganic perovskite solar cells (PSCs) were fabricated in inert atmosphere. Herein, we report an additive-assisted airflow drying (AAD) method to make mixed-halide inorganic perovskite films in ambient air. The nucleation and crystal growth during film formation are controlled by using airflow dying and lead acetate trihydrate additive, producing pinhole-free film with low defect density. Consequently, efficiency of CsPbI2.25Br0.75 PSCs is improved to 18.49%, which is the highest for wide-bandgap (>1.8 eV) inorganic PSCs. An efficiency of 17.08% is achieved for PSCs made under moderate relative humidity (40–50%). Moreover, PCEs of 17.39% and 11.54% are achieved for CsPbI2Br and CsPbIBr2 PSCs, respectively, which are among the best PCEs for CsPbI2Br and CsPbIBr2 PSCs. This work provides a convenient and efficient method to make efficient inorganic PSCs in ambient air.