Role of Ionic Charge Accumulation in Perovskite Solar Cell: Carrier Transfer in Bulk and Extraction at Interface

By combining a simplified drift-diffusion model with the density functional theory, we quantitatively explore the contributing effects of the mobile defects in perovskites on the hysteresis of perovskite solar cells from aspects of both carrier transfer in the perovskite and extraction at the interface. Based on the solution of the one-dimensional Poisson equation, we demonstrate that at a positive biasing voltage applied to the hole contact layer that is larger than the presetting voltage, the carriers in perovskite need to overcome an energy barrier to transfer toward their selective contacts. The d ependence of the energy barrier on the scanning voltage is determined by properties of both perovskite and contacts. By using the first-principles calculations, we further find that the perovskite/TiO2 band offsets are larger at a higher positive presetting voltage. The results reveal that the contributions of the defect migration to the hysteresis depend not only on the structural properties of perovskite but also on the choice of the contact materials via both carrier transfer in the bulk perovskite and carrier extraction at the interface between the perovskite and the contact materials.