Precise Control of Perovskite Crystallization Kinetics via Sequential A‐Site Doping
Minchao Qin, Haibo Xue, Hengkai Zhang, Hanlin Hu, Kuan Liu, Yuhao Li, Zhaotong Qin, Junjie Ma, Hepeng Zhu, Keyou Yan, Guojia Fang, Gang Li, U‐Ser Jeng, Geert Brocks, Shuxia Tao, Xinhui Lu
Abstract
Abstract Two‐step‐fabricated FAPbI 3 ‐based perovskites have attracted increasing attention because of their excellent film quality and reproducibility. However, the underlying film formation mechanism remains mysterious. Here, the crystallization kinetics of a benchmark FAPbI 3 ‐based perovskite film with sequential A‐site doping of Cs + and GA + is revealed by in situ X‐ray scattering and first‐principles calculations. Incorporating Cs + in the first step induces an alternative pathway from δ‐CsPbI 3 to perovskite α‐phase, which is energetically more favorable than the conventional pathways from PbI 2 . However, pinholes are formed due to the nonuniform nucleation with sparse δ‐CsPbI 3 crystals. Fortunately, incorporating GA + in the second step can not only promote the phase transition from δ‐CsPbI 3 to the perovskite α‐phase, but also eliminate pinholes via Ostwald ripening and enhanced grain boundary migration, thus boosting efficiencies of perovskite solar cells over 23%. This work demonstrates the unprecedented advantage of the two‐step process over the one‐step process, allowing a precise control of the perovskite crystallization kinetics by decoupling the crystal nucleation and growth process.