A Universal Strategy of Perovskite Ink ‐ Substrate Interaction to Overcome the Poor Wettability of a Self‐Assembled Monolayer for Reproducible Perovskite Solar Cells

Abstract Perovskite solar cells employing [4‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl)butyl]phosphonic acid (Me‐4PACz) self‐assembled monolayer as the hole transport layer have been reported to demonstrate a high device efficiency. However, the poor perovskite wetting on Me‐4PACz caused by poor perovskite ink interaction with the underlying Me‐4PACz presents significant challenges for fabricating efficient perovskite devices. A triple co‐solvent system comprising dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N‐methyl‐2‐pyrrolidone (NMP) is employed to improve the perovskite ink ‐ Me‐4PACz coated substrate interaction and obtain a uniform perovskite layer. In comparison to DMF‐ and DMSO‐based inks, the inclusion of NMP shows considerably higher binding energies of the perovskite ink with Me‐4PACz as revealed by density‐functional theory calculations. With the optimized triple co‐solvent ratio, the perovskite devices deliver high power conversion efficiencies of >20%, 19.5%, and ≈18.5% for active areas of 0.16, 0.72, and 1.08 cm2, respectively. Importantly, this perovskite ink–substrate interaction approach is universal and helps in obtaining a uniform layer and high photovoltaic device performance for other perovskite compositions such as MAPbI3, FA1−xMAxPbI3–yBry, and MA‐free FA1−xCsxPbI3–yBry.