Excellent Stability of Perovskite Solar Cells by Passivation Engineering

The efficiencies of organic-inorganic lead halide perovskite solar cells (PSCs) have significantly increased so far, but the long-term stability of PSCs needs to be urgently improved. In this work, a novel and convenient strategy is developed to improve PSCs' stability by introducing thiourea into perovskite. Thiourea passivates perovskite by the formation of the PbS bond on the outermost layer of perovskite and lath-shaped grain among perovskites, which contributes to the improvement of oxygen, light, thermal stability, and little hysteresis. The mechanism is elucidated by the density functional theory calculation. In addition, the additive of thiourea into perovskite significantly improves the quality of perovskite crystal for the adduct of PbI2 with thiourea as the Lewis base. Devices of a perovskite film with the thiourea additive achieve high efficiencies of 19.57% and 17.67% for active areas of 0.1 and 1.0cm(2), respectively. Most importantly, unencapsulated devices retain 98% and 93% of original efficiencies after two months under air conditions for active areas of 0.1 and 1.0cm(2), respectively, showing excellent stability. The present work provides a simple and effective method to improve long-term stability of PSCs.