Assessing the\nInfluence of Illumination on Ion Conductivity\nin Perovskite Solar Cells

Whether illumination\ninfluences the ion conductivity in lead-halide\nperovskite solar cells containing iodide halides has been an ongoing\ndebate. Experiments to elucidate the presence of a photoconductive\neffect require special devices or measurement techniques and neglect\npossible influences of the enhanced electronic charge concentrations.\nHere, we assess the electronic-ionic charge transport using drift-diffusion\nsimulations and show that the well-known increase in capacitance at\nlow frequencies under illumination is caused by electronic currents\nthat are amplified due to the screening of the alternating electric\nfield by the ions. We propose a novel characterization technique to\ndetect a potential photoinduced increase in ionic conductivity based\non capacitance measurements on fully integrated devices. The method\nis applied to a range of perovskite solar cells with different active\nlayer materials. Remarkably, all measured samples show a clear signature\nof photoenhanced ion conductivity, posing fundamental questions on\nthe underlying nature of the photosensitive mechanism.