Reducing Defects of All-Inorganic γ-CsPbI 2 Br Thin Films by Ethylammonium Bromide Additives for Efficient Perovskite Solar Cells.

Obtaining good-quality perovskite thin films is a fundamental facet that contributes to efficient inorganic perovskite solar cells. Herein, we successfully deposited ethylammonium bromide (EABr) additive-assisted high quality γ- CsPbI 2 Br perovskite films under ambient conditions. Detailed morphological, structural, optical, charge transport, photovoltaic performance, and stability properties have been studied. It is observed that the EABr additive helps to retard the crystal growth of perovskite films to produce a highly crystalline perovskite film with microsized grains (>1 μm) and with reduced grain boundaries. The fabricated devices based on an optimum amount of EABr (4 mg mL -1 ) exhibited the highest 14.47 % power conversion efficiency. Moreover, the EABr-4 mg mL -1 -assisted γ- CsPbI 2 Br-based devices achieved a high thermal long-term stability and maintained ∼75% of their initial efficiency over 180 h at 85 °C thermal stress under ambient conditions (relative humidity: ∼35%) without encapsulation. This additive-assisted method suggests a new pathway to achieve high-quality perovskite films with a stabilized photoactive black phase and efficient devices.