Role of Ion-Assisted Recombination and Grain Boundaries in Perovskite Solar Cell Hysteresis and Efficiency

Organic-inorganic hybrid perovskite (OIHP) solar cells are one of the fastest-growing solar cell technologies ever. OIHPs offer a wide range of bandgaps, wide optical absorption and low-cost deposition, making them an ideal candidate for solar cells. Despite the amazing properties of these materials, the perovskite solar cell performance is hampered by grain boundaries, traps, and hysteresis behavior of current-voltage (JV). Though the exact mechanism behind the hysteresis is still unknown, ionic movements in the perovskite film are considered to be the primary reason behind it. We present a drift-diffusion (DD) model to study the role of cation-mediated non-radiative recombination in the JV hysteresis in CH3NH3PbI3 cells. We study how the mobile cations can trap electrons leading to the JV hysteresis and poor performance of the cell. Impact of cation-electron trapping constant and the JV scan rate is investigated. We also simulate how the accumulation of mobile ions at the grain boundaries and interfaces limits the solar cell output current. When the ions are distributed in the bulk grains, they hardly affect the cell performance. When they start accumulating at the grain boundaries, the Jsc drops rapidly. The presented results give an insight into the effect of grain boundaries, and cation-mediated recombination as a possible reason for the JV hysteresis in perovskite solar cells.