Flattening of the Cratered Inorganic Perovskite Film via Precursor Engineering for CsPbI₂Br Solar Cells with 16.86% Efficiency

Understanding the fundamental chemistry of the perovskite precursor is crucial to accurately controlling the crystal morphology of perovskite films and thus contributing to efficient and stable solar cells. Here, we report the growth of uniform and pinhole-free CsPbI2Br perovskite films via precursor engineering by introducing a small amount of 4,4′-dihydroxybiphenyl. The rationally designed precursor exhibits a colloidal feature with an average size of 175 nm due to hydrogen bonding between CsPbI2Br and 4,4′-dihydroxybiphenyl. As a result, coherent crystal growth across the bottom to the surface of the perovskite film is realized, affording high-quality teeth-like crystals with enlarged crystal size and significantly reduced carrier traps. Eventually, the prepared inorganic CsPbI2Br solar cells with tailored precursors exhibit a high power conversion efficiency of 16.86%, along with an impressive open-circuit voltage of 1.38 V. Moreover, compared to control devices, the unencapsulated target devices show remarkably enhanced thermal and UV stability in an ambient atmosphere.