Charge Accumulation and Hysteresis in Perovskite-Based Solar Cells: An Electro-Optical Analysis

Organic-inorganic hybrid perovskite solar cells based on CH3NH3PbI3 have achieved great success with efficiencies exceeding 20%. However, there are increasing concerns over some reported efficiencies as the cells are susceptible to current-voltage (I-V) hysteresis effects. It is therefore essential that the origins and mechanisms of the I-V hysteresis can clearly be understood to minimize or eradicate these hysteresis effects completely for reliable quantification. Here, a detailed electro-optical study is presented that indicates the hysteresis originates from lingering processes persisting from sub-second to tens of seconds. Photocurrent transients, photoluminescence, electroluminescence, quasi-steady state photoinduced absorption processes, and X-ray diffraction in the perovskite solar cell configuration have been monitored. The slow processes originate from the structural response of the CH3NH3PbI3 upon E-field application and/or charge accumulation, possibly involving methylammonium ions rotation/displacement and lattice distortion. The charge accumulation can arise from inefficient charge transfer at the perovskite interfaces, where it plays a pivotal role in the hysteresis. These findings underpin the significance of efficient charge transfer in reducing the hysteresis effects. Further improvements of CH3NH3PbI3-based perovskite solar cells are possible through careful surface engineering of existing TiO2 or through a judicious choice of alternative interfacial layers.