Elimination of Light-Soaking Effect in Hysteresis-Free Perovskite Solar Cells by Interfacial Modification

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 eliminates the light-soaking effect. Furthermore, a model that combines ion migration and the charge accumulation process to interpret the light-soaking effect and performance improvement in PSCs is proposed.