Molten‐Salt‐Assisted CsPbI 3 Perovskite Crystallization for Nearly 20%‐Efficiency Solar Cells

Abstract Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten‐salt‐assisted crystallization (MSAC) strategy is presented to improve grain growth of the all‐inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables more intensive mass transfer by means of convection and diffusion, which is beneficial to the interaction among the precursor colloids and to inducing in‐plane growth of perovskite grains, resulting in the formation of high‐quality perovskite films with suppressed pinhole and crack formation. Additionally, the introduction of molten salt alters the intermediate phases, and thus changes the crystallization pathways by reducing the energy barrier to produce films with desired optical and electrical properties. As a result, the MSAC strategy endows the devices with champion steady‐state output efficiency of 19.83% and open‐circuit voltage ( V oc ) as high as 1.2 V, among the highest for this type of solar cell, thanks to its effectively reduced V oc deficit.