Flattening of the Cratered Inorganic Perovskite Film\nvia Precursor Engineering for CsPbI<sub>2</sub>Br Solar Cells with\n16.86% Efficiency

Understanding\nthe fundamental chemistry of the perovskite precursor\nis crucial to accurately controlling the crystal morphology of perovskite\nfilms and thus contributing to efficient and stable solar cells. Here,\nwe report the growth of uniform and pinhole-free CsPbI<sub>2</sub>Br perovskite films via precursor engineering by introducing a small\namount of 4,4′-dihydroxybiphenyl. The rationally designed precursor\nexhibits a colloidal feature with an average size of 175 nm due to\nhydrogen bonding between CsPbI<sub>2</sub>Br and 4,4′-dihydroxybiphenyl.\nAs a result, coherent crystal growth across the bottom to the surface\nof the perovskite film is realized, affording high-quality teeth-like\ncrystals with enlarged crystal size and significantly reduced carrier\ntraps. Eventually, the prepared inorganic CsPbI<sub>2</sub>Br solar\ncells with tailored precursors exhibit a high power conversion efficiency\nof 16.86%, along with an impressive open-circuit voltage of 1.38 V.\nMoreover, compared to control devices, the unencapsulated target devices\nshow remarkably enhanced thermal and UV stability in an ambient atmosphere.