Hot-casting assisted liquid additive engineering for efficient and stable perovskite solar cells

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, we show that we can reduce the amount of residual DMSO in as-spin-coated films significantly - by 30 times - through use of pre-heated substrates, or a so-called hot-casting method. Hot-casting increases the perovskite film thickness which allows us to reduce the perovskite solution concentration. By reducing the amount of DMSO in proportion to the concentration of perovskite precursors and using hot-casting, we are able to fabricate perovskite layers with improved perovskite-substrate buried interfaces by suppressing the formation of byproducts which increase trap density and accelerate degradation of the perovskite layers. The best-performing PSCs exhibit power conversion efficiency (PCE) of 23.4% (23.0% stabilized efficiency) under simulated solar illumination. Furthermore, encapsulated devices showed considerably reduced post-burn-in decay of -0.84% of initial efficiency per 100 h, retaining more than 80% and 93% of their initial and post-burn-in efficiencies after 800 h of operation with maximum power point tracking (MPPT) under high-power of ultraviolet-(UV-)containing continuous light exposure (overall power density of 1.1 sun with 2.6 times higher UV-region power density than AM 1.5G).