NbF5: A Novel α-Phase Stabilizer for FA-Based Perovskite Solar Cells with High Efficiency

The HC(NH2)(2)(+)(FA(+)) is a well-known substitute to CH3NH3+(MA(+)) for its capability to extend light utilization for improved power conversion efficiency for perovskite solar cells; unfortunately, the dark cubic phase (alpha -phase) can easily transition to the yellow orthorhombic phase (delta -phase) at room temperature, an issue that prevents its commercial application. In this report, an inorganic material (NbF5) is developed to stabilize the desired alpha -phase perovskite material by incorporating NbF5 additive into the perovskite films. It is found that the NbF5 additive effectively suppresses the formation of the yellow delta -phase in the perovskite synthesis and aging process, thus enhancing the humidity and light-soaking stability of the perovskite film. As a result, the perovskite solar cells with the NbF5 additive exhibit improved air stability by tenfold, retaining nearly 80% of their initial efficiency after aging in air for 50 d. In addition, under full-sun AM 1.5 G illumination of a xenon lamp without any UV-reduction, the perovskite solar cells with the NbF5 additive also show fivefold improved illumination stability than the control devices without NbF5.