Multifunctional Passivator Trifluoroacetamidine for Improving the Performance of All‐Inorganic CsPbI3 Perovskite Solar Cells

All‐inorganic CsPbI 3 perovskite solar cells (PSCs) possess great potential of development with the suitable bandgap and outstanding chemical stability in recent years. However, due to the low tolerance factor of the crystal structure and the high defect density of states within the absorbing layer, CsPbI 3 perovskite film displays poor phase stability at room temperature and severe exciton nonradiative loss under illumination conditions. Therefore, a novel multifunctional passivator trifluoroacetamidine (TFA) is introduced to decrease the defect density and improve the photovoltaic performance of CsPbI 3 PSCs. The amino groups in TFA not only form hydrogen bonds with I − to suppress the oxidation of I − in the perovskite, but also interact with noncoordinated Pb 2+ in conjunction with C=O bonds to passivate Pb‐related defects. Furthermore, the hydrophobic characteristic of –CF 3 in TFA could efficiently protect the perovskite layer from moisture damage in the external environment. Consequently, the 0.3 mol% TFA additive based‐device possesses an optimal power conversion efficiency of 19.82% and the excellent fill factor of 0.81. In addition, the optimized PSCs retain 80% of their original efficiency under 1000 h of illumination in ambient conditions without encapsulation.