Eliminating Light-Soaking Instability in Planar Heterojunction Perovskite Solar Cells by Interfacial Modifications.

Stability remains as a challenge of perovskite solar cells although encouraging progress has been made toward their maximum achievable power conversion efficiency in recent years. Light-soaking issue, where the device performance improves upon continuous light illumination and reduces upon storage in dark, is widely observed and marked as the early-stage instability during device operation. In this work, we have employed conjugated polymer PCDTBT as the dopant-free hole-transport layer to fabricate devices without hysteresis but with reversible light-soaking instability. The introduction of n-type molecules, either organic molecule PDI2 or fullerene derivative PC61BM, as the interfacial layer between TiO2 and perovskite layers can effectively reduce or eliminate this instability owing to the efficient charge transport and defect passivation at the electron-transport layer interface, accompanied with an efficiency of 15.7 and 17.7%, respectively. We conclude that the light-soaking instability of these perovskite solar cells is mainly originated from the charge accumulation at the TiO2/perovskite interface and can be eliminated once the interfacial charge can be suppressed by interfacial modifications to improve charge transport at the interface.