Effects of Voltage Biasing on Current Extraction in Perovskite Solar Cells

The recent rapid increase in efficiency of organic-inorganic perovskite solar cells (PSCs) has resulted in a need to develop a clear understanding of their stability and working mechanisms. In particular, it has been suggested that ion migration contributes to the commonly observed hysteresis in the current-voltage measurements of PSCs, but the rate of ion migration and its effects on the electronic properties of PSCs remain to be addressed. In this work, electron-beam-induced current (EBIC) is used to directly map changes in local current extraction in organic-inorganic PSCs under applied voltage. By combining EBIC mapping, standard current-voltage measurements, and external quantum efficiency measurements, it is shown that between the two potential roles that point defects play in device enhancement under voltage biasing, the effects caused by defect-mediated ion migration outweigh the effects from the filling of trap states caused by these defects. Evidence is also provided for ion migration preferentially at local features such as extended defects. The measured timescale of tens of seconds for migration across a full device imply that ion migration contributes indirectly to the electronic capacitance of perovskite devices through interface charging.