Publication date: 25th September 2020
Metal halide perovskites, such as methylammonium lead triiodide (MAPbI3), achieved attention of the PV community during last few years. Despite the rapid progress, the device performance of perovskite solar cells still remains below their theoretical limit. One of the key factors to further improve their power conversion efficiency is to develop high-quality perovskite active layers with large grain size, and hence reduced defect density. In our contribution, through impedance spectroscopy and deep-level transient spectroscopy, we characterize ionic defects in MAPbI3-based devices in which the grain size was purposely varied: by adding hypophosphorous acid (HPA) in the precursor solution, the average grain size increases . Our results indicate that the activation energy and concentration of an ionic defect species which we assign to methylammonium vacancies decrease with the amount of HPA. Therefore, controlled grain growth during fabrication facilitates an opportunity in tuning the ionic defects in perovskite devices.