Possible interfacial ion/charge accumulation in thin-film perovskite/fullerene surfactant planar heterojunction solar cells

Organic-inorganic hybrid perovskite solar cells (PVSCs) have become the most promising photovoltaic technology nowadays, considering its low-cost and low-temperature manufacturing processes and superior power conversion efficiency. In addition to efficiency optimization, understanding the fundamental properties of the perovskite materials and the related device physics, such as hysteresis and stability, has also attracted significant research interest. In this study, we manifested the fact that the hysteretic behavior of PVSC is strongly correlated with the structure design of the adjacent charge-transporting layer (CTL). The constituent ions in CTL are very likely to induce severe device hysteresis based on the analyses from the capacitance-voltage and electrochemical impedance spectroscopy. By further applying Warburg impedance to simulate the impedance spectrum at the low-frequency region, distinct kinetics of ion movement at different perovskite/electron-transporting layer interfaces are clearly revealed. This work unveils the close interactions between the perovskite material and the ions from adjacent CTLs, providing a new perspective on the future molecular design of CTLs for PVSCs.