Current Photovoltaic Research ISSN:2288-3274(Print) 2508-125X(Online)

The interest in perovskite solar cells has been skyrocketed owing to their rapid progress in efficiency in recent years. Here, we report the effect of non-stoichiometry in the methylammonium lead trihalide (MAPbI₃) precursors used in a solution process with different MAI : PbI₂ ratios of 1 : 0.96, 1 : 1.10, 1 : 1.15, and 1:1.20. With an increase in the PbI₂ content, the PbI₂ secondary phase was found to form at grain boundary region of perovskite thin films, as evidenced by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In terms of device performance, open-circuit voltage in particular is significantly improved with increasing the molar ratio of PbI₂, which is possibly ascribed to the reduction in recombination sites at grain boundary of perovskite and hence the prolonged life time of light-generated carriers according to the reported. As a result, the PbI2-excess devices exhibited a higher power conversion efficiency compared to the MAI-excess ones.