Small‐Molecule Targeting of Defect Passivation in All‐Inorganic Carbon‐Based Perovskite Solar Cells

The fast‐track development in all‐inorganic perovskite photovoltaics for high efficiency are still facing the defect issues including vacancy, undercoordinated ions, and dislocation at the surface/interface of perovskite materials. Herein, three kinds of small‐molecules difluorobenzylamine (DFBA) are found to act as the interfacial modification materials to stabilize and enhance the efficiency of all‐inorganic carbon perovskite CsPbI_3–xBr_x solar cell. The fluorine atoms with different positions in the benzene ring are demonstrated by the density‐functional theory simulations and experiments to passivate the defect at the surface/interface of perovskites, boosting the photocarrier transfer. Accordingly, the most suitable 2,6‐DFBA is used to modify the perovskite to prepare hole‐transporting materials‐free carbon‐based CsPbI_3–xBr_x (X = 0.3) perovskite solar cells, and the interface‐modified device yields a power conversion efficiency (PCE) of 14.6%, the open‐circuit voltage is increased to 1.14 V, and the PCE of the unpackaged device remained at 92% of the initial PCE after 1680 h of storage at 20–30% air humidity.