Controlling Lead Halide Residue in Perovskite Solar Cells: A Method to Improve the Photostability and Hysteresis

The presence of residual lead iodide phase in perovskite films, inherent to the two-step spin-coating method, has been reported to be beneficial for the performance of perovskite solar cells (PSCs); However, it may potentially undermine the photostability of PSCs. Herein, four distinct sets of perovskite films and devices are fabricated via the two-step spin-coating process, each under different processing conditions. All conditions demonstrate promising power conversion efficiency in PSCs. However, the aspect of photostability is found to be significantly influenced by unreacted PbI2 in the perovskite films. Varying degrees of residual PbI2 are detected among these films. Upon light exposure, it is observed that residual PbI2 within perovskites undergoes decomposition into metallic lead (Pb-0) and mobile iodine, and these can affect the photovoltaic performance of the PSCs. The presence of mobile ions in metal-halide perovskites has generated substantial concern due to their impact on hysteresis within the J-V curve. Furthermore, the metallic lead (Pb-0) containing perovskite films exhibits a prominent inverted hysteresis in the J-V curve