FA-Assistant Iodide Coordination in Organic-Inorganic Wide-Bandgap Perovskite with Mixed Halides

作者：Xie, Yue-Min; Zeng, Zixin; Xu, Xiuwen; Ma, Chunqing; Ma, Yuhui; Li, Menglin; Lee, Chun-Sing; Tsang, Sai-Wing^*

来源：Small, 2020, 16(10): 1907226.

DOI：10.1002/smll.201907226

• crystallization
• halide coordination
• wide-bandgap perovskites

Mixed-halide wide-bandgap perovskites are key components for the development of high-efficiency tandem structured devices. However, mixed-halide perovskites usually suffer from phase-impurity and high defect density issues, where the causes are still unclear. By using in situ photoluminescence (PL) spectroscopy, it is found that in methylammonium (MA(+))-based mixed-halide perovskites, MAPb(I0.6Br0.4)(3), the halide composition of the spin-coated perovskite films is preferentially dominated by the bromide ions (Br-). Additional thermal energy is required to initiate the insertion of iodide ions (I-) to achieve the stoichiometric balance. Notably, by incorporating a small amount of formamidinium ions (FA(+)) in the precursor solution, it can effectively facilitate the I- coordination in the perovskite framework during the spin-coating and improve the composition homogeneity of the initial small particles. The aggregation of these homogenous small particles is found to be essential to achieve uniform and high-crystallinity perovskite film with high Br- content. As a result, high-quality MA(0.9)FA(0.1)Pb(I0.6Br0.4)(3) perovskite film with a bandgap (E-g) of 1.81 eV is achieved, along with an encouraging power-conversion-efficiency of 17.1% and open-circuit voltage (V-oc) of 1.21 V. This work also demonstrates the in situ PL can provide a direct observation of the dynamic of ion coordination during the perovskite crystallization.