摘要： The hysteresis and light-soaking effect have been observed in organo-metal halide perovskite solar cells (PSCs) under operating conditions, which inhibit the precise evaluation of power output. The mechanisms leading to these effects are little understood. Here, our studies have demonstrated that the light-soaking effect is related to the electron selective layer/perovskite interface in hysteresis-free PSCs. The introduction of [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) doped with CH3NH3I molecules as the interfacial layer can effectively release or eliminate this effect due to the efficient charge transfer, accompanied with the best stable output efficiency of 19% and an ultrahigh fill factor over 84%. Capacitance -voltage and capacitance -frequency curves derived from electrochemical impedance spectroscopy demonstrate that the light-soaking effect in PSCs mainly originates from the charge accumulation at the PC61BM/perovskite interface. The CH3NH3I doped in PC61BM forestalls the ion movement among the perovskite and thus eliminate the light-soaking effect. Furthermore, a model that combines ion migration and charge accumulation process to interpret the light-soaking effect and performance improvement in PSCs is proposed.