Directing the Crystallization Pathway of Formamidinium Lead Iodide in Anti-Solvent Free Processes

Understanding the nucleation, crystallization, and phase transition mechanisms in FAPbI₃ perovskite films is crucial for improving their stability and performance. Adding alkylammonium chlorides (RACl) to the perovskite ink, especially methylammonium chloride (MACl), is known to result in low-temperature crystallization, grain growth and preferential orientation of α-FAPbI₃ when perovskite thin films are deposited in anti-solvent based processes. ^1–4 As efforts increase to scale perovskite deposition, antisolvent-free methods are of considerable interest but result in distinct solute-solvent and solvent-solvent interactions relative to processes that employ anti-solvents.^1,2,4 Here we show that inclusion of RACl additives wields significant influence over the crystallization dynamics and temperature-dependent phase stability of lead-halide perovskite films formed by anti-solvent-free processing by means of <i>in situ</i> grazing incidence wide-angle X-ray scattering. The <i>in situ</i> experiments reveal that the ionic radii and vapor pressure of the RACl conjugate base are critical factors affecting the crystallization mechanism, final film morphology, and optoelectronic properties of the perovskite films. Promising alternatives to MACl, where the MA has particularly detrimental reactivity, are identified. Overall, we provide a framework for future development of crystallization design using anti-solvent-free processes, focusing on the influence of the additive cations in the perovskite film formation mechanism.<br/><br/>(1) Park, J.; Kim, J.; Yun, H.-S.; Paik, M. J.; Noh, E.; Mun, H. J.; Kim, M. G.; Shin, T. J.; Seok, S. I. <i>Nature</i> <b>2023</b>, <i>616</i> (7958)<br/>(2) Bi, L.; Fu, Q.; Zeng, Z.; Wang, Y.; Lin, F. R.; Cheng, Y.; Yip, H.-L.; Tsang, S. W.; Jen, A. K.-Y. <i>J. Am. Chem. Soc.</i> <b>2023</b>, <i>145</i> (10), 5920–5929.<br/>(3) hang, Y.; Li, Y.; Zhang, L.; Hu, H.; Tang, Z.; Xu, B.; Park, N.-G. <i>Adv. Energy Mater.</i> <b>2021</b>, <i>11</i> (47), 2102538.<br/>(4) Kim, M.; Kim, G.-H.; Lee, T. K.; Choi, I. W.; Choi, H. W.; Jo, Y.; Yoon, Y. J.; Kim, J. W.; Lee, J.; Huh, D.; Lee, H.; Kwak, S. K.; Kim, J. Y.; Kim, D. S. <i>Joule</i> <b>2019</b>, <i>3</i> (9), 2179–2192.