Stabilizing α-Phase FAPbI<sub>3</sub> Perovskite Induced by an Ordered Solvated Quasi-Crystalline PbI<sub>2</sub>
Yalan Zhang, Tinghuan Yang, Sanguk Lee, Shengzhong Liu, Kui Zhao, Nam‐Gyu Park
Abstract
In the two-step procedure for preparing a perovskite film, the chemistry of the PbI 2 solution plays an important role in determining the phase stability of perovskite films. We report here sulfoxonium salt-controlled crystallization for stabilizing α-phase formamidinium lead iodide (FAPbI 3 ) in perovskite solar cells via additive engineering of the PbI 2 solution. The in situ grazing incidence wide-angle X-ray scattering studies reveal that the trimethylsulfoxonium iodide (TMSOI) additive leads to an ordered solvated quasi-crystalline PbI 2, which facilitates the transformation to α-phase FAPbI 3 at room temperature while reacting PbI 2 with FAI. As a result, the photovoltaic performance and stability of the perovskite solar cells are enhanced due to the improved optoelectronic properties of the perovskite films. A best-performing device shows a power conversion efficiency of 24.65% at one sun illumination. The unencapsulated devices stored at room temperature under 30–40% relative humidity maintain 96.40% of their initial efficiency after 1000 h.