Charge Transport Limitations in Perovskite Solar Cells: The Effect of Charge Extraction Layers

Understanding the charge transport characteristics and their limiting factors in organolead halide perovskites is of great importance for the development of competitive and economically advantageous photovoltaic systems derived from these materials. In the present work, we examine the charge carrier mobilities in CH₃NH₃PbI₃ (MAPI) thin films obtained from a one-step synthesis procedure and in planar n-i-p devices based on these films. By performing time-of-flight measurements, we find mobilities around 6 cm²/V s for electrons and holes in MAPI thin films, whereas in working solar cells, the respective effective mobility values are reduced by 3 orders of magnitude. From complementary experiments on devices with varying thicknesses of electron and hole transport layers, we identify the charge extraction layers and the associated interfaces rather than the perovskite material itself as the major limiting factors of the charge carrier transport time in working devices.