Inverted Current-Voltage Hysteresis in Mixed Perovskite Solar Cells: Polarization, Energy Barriers, and Defect Recombination

Organic-inorganic metal halide perovskite solar cells show hysteresis in their current-voltage curve measured at a certain voltage sweep rate. Coinciding with a slow transient current response, the hysteresis is attributed to a slow voltage-driven (ionic) charge redistribution in the perovskite solar cell. Thus, the electric fi eld profi le and in turn the electron/hole collection effi ciency become dependent on the biasing history. Commonly, a positive prebias is benefi cial for a high power-conversion effi ciency. Fill factor and open-circuit voltage increase because the prebias removes the driving force for charge to pile-up at the electrodes, which screen the electric fi eld. Here, it is shown that the piled-up charge can also be benefi cial. It increases the probability for electron extraction in case of extraction barriers due to an enhanced electric fi eld allowing for tunneling or dipole formation at the perovskite/electrode interface. In that case, an inverted hysteresis is observed, resulting in higher performance metrics for a voltage sweep starting at low prebias. This inverted hysteresis is particularly pronounced in mixed-cation mixed-halide systems which comprise a new generation of perovskite solar cells that makes it possible to reach power-conversion effi ciencies beyond 20%.