Reducing Defects in Perovskite Solar Cells with White Light Illumination-Assisted Synthesis

Defects lower the performance of perovskite solar cells by playing as recombination centers of carriers and migration channels of ions under illumination. Here we used various kinds of lights to assist the synthesis of perovskite in the sequential vapor deposition of perovskite. Without applying light, iodine accumulated on the film surface, and plenty of defects existed in the as-fabricated device. White light forced more iodine into the film bulk, removing excess iodine on the surface and leading to improved iodine homogenization, and consequently, most defects were annihilated. Devices with perovskite synthesized under white light showed improved efficiency and light stability compared to those prepared in the dark. Trication-based devices with over 20% efficiency under simulated solar light were successfully fabricated; on the contrary, control devices prepared in the dark showed only 18.3% efficiency. This finding suggests the possibility of kinetically controlling the synthesis of perovskite using low-intensity white illumination.