Hysteresis and Its Correlation to Ionic Defects in Perovskite Solar Cells

Ion migration has been reported to be one of the main reasons for hysteresis in the current-voltage (J-V) characteristics of perovskite solar cells. We investigate the interplay between ionic conduction and hysteresis types by studying Cs-0.05(FA(0.83)MA(0.17))(0.95)Pb(I0.9Br0.1)(3) triple-cation perovskite solar cells through a combination of impedance spectroscopy (IS) and sweep-rate-dependent J-V curves. By comparing polycrystalline devices to single-crystal MAPbI(3) devices, we separate two defects, beta and gamma, both originating from long-range ionic conduction in the bulk. Defect beta is associated with a dielectric relaxation, while the migration of gamma is influenced by the perovskite/hole transport layer interface. These conduction types are the causes of different types of hysteresis in J-V curves. The accumulation of ionic defects at the transport layer is the dominant cause for observing tunnel-diode-like characteristics in the J-V curves. By comparing devices with interface modifications at the electron and hole transport layers, we discuss the species and polarity of involved defects.