Crystallization Control\nto Prepare Uniform CsPbI<sub>2</sub>Br Thin Films for High-Efficiency\nPerovskite Solar Cells

All-inorganic perovskite solar cells (PSCs) face challenges\nrelated\nto film inhomogeneity, which arises from nonideal crystallization.\nThis issue significantly impedes the advancement of all-inorganic\nPSCs. In this study, we observed that during the crystallization process\nof CsPbI<sub>2</sub>Br, the Br-rich intermediate phase is often preferentially\ndeposited, leading to an uneven distribution in the out-of-plane direction\nof the perovskite film. To address this issue, crown ether molecules\n(dibenzo-18-crown-6) were introduced into the perovskite precursor\nsolution. The complexation of crown ether with Cs cations and Br anions\noptimizes the crystallization sequence of the perovskite, ensuring\nthat the intermediate phase closely conforms to the standard stoichiometric\nratio. This adjustment significantly mitigates the problem of uneven\nhalogen ion distribution along the out-of-plane direction. Furthermore,\nthe crown ether thermally decomposes during the high-temperature annealing\nprocess, thereby not affecting the composition of the final perovskite\nfilm. Following crown ether treatment, the efficiency of the PSCs\nreached 14.08%, and the unpackaged devices maintained 80% of their\ninitial efficiency after 1000 h of exposure to light in an atmospheric\nenvironment.