Hot‐Casting‐Assisted Liquid Additive Engineering for Efficient and Stable Perovskite Solar Cells

Abstract High‐performance inorganic–organic lead halide perovskite solar cells (PSCs) are often fabricated with a liquid additive such as dimethyl sulfoxide (DMSO), which retards crystallization and reduces roughness and pinholes in the perovskite layers. However, DMSO can be trapped during perovskite film formation and induce voids and undesired reaction byproducts upon later processing steps. Here, it is shown that the amount of residual DMSO can be reduced in as‐spin‐coated films significantly through use of preheated substrates, or a so‐called hot‐casting method. Hot casting increases the perovskite film thickness given the same concentration of solutions, which allows for reducing the perovskite solution concentration. By reducing the amount of DMSO in proportion to the concentration of perovskite precursors and using hot casting, it is possible to fabricate perovskite layers with improved perovskite–substrate interfaces by suppressing the formation of byproducts, which increase trap density and accelerate degradation of the perovskite layers. The best‐performing PSCs exhibit a power conversion efficiency (PCE) of 23.4% (23.0% stabilized efficiency) under simulated solar illumination. Furthermore, encapsulated devices show considerably reduced post‐burn‐in decay, retaining 75% and 90% of their initial and post‐burn‐in efficiencies after 3000 h of operation with maximum power point tracking (MPPT) under high power of ultraviolet (UV)‐containing continuous light exposure.