Halford Gabriel C, Deng Qingmu, Gomez Annie, Green Tianna, Mankoff Jill M, Belisle Rebecca A
Chemistry Department, Wellesley College, Wellesley, Massachusetts 02481, United States.
Olin College of Engineering, Needham, Massachusetts 02492, United States.
ACS Appl Mater Interfaces. 2022 Jan 26;14(3):4335-4343. doi: 10.1021/acsami.1c22854. Epub 2022 Jan 13.
Despite substantial research effort, photoinduced halide segregation in mixed halide perovskites continues to limit the available perovskite chemistries for use in optoelectronic applications. In this study, we present new insights into halide-segregation process through in situ X-ray diffraction measurements that reveal substantial structural changes in mixed-halide perovskites under excitation. We observe that photoinduced halide segregation leads to the formation of one iodide-rich and one bromide-rich perovskite composition whose Br:I ratios are the same (at 20 and 93% bromine, respectively), for a range of compositions of the pristine initial perovskite phase. This segregation reverses in the dark to re-form a mixed halide perovskite with the same lattice spacing as the pristine perovskite. From these results, we determine a kinetic rate for the formation and dissolution of these new crystalline phases and observe that the crystalline orientation is preserved through the light-segregation and dark-relaxation processes. Our results are consistent with a model of halide segregation where excitation causes changes in the free energy of mixing and ultimately the formation of a miscibility gap in the MAPb(IBr) phase diagram and should inform future works to model and manipulate the halide-segregation process in mixed-halide perovskites.
尽管进行了大量研究，但混合卤化物钙钛矿中的光致卤化物偏析仍然限制了可用于光电子应用的钙钛矿化学组成。在本研究中，我们通过原位X射线衍射测量对卤化物偏析过程提出了新的见解，该测量揭示了混合卤化物钙钛矿在激发下的显著结构变化。我们观察到，光致卤化物偏析导致形成一种富碘和一种富溴的钙钛矿组成，对于原始初始钙钛矿相的一系列组成，其Br:I比相同（分别为20%和93%的溴）。这种偏析在黑暗中会逆转，重新形成与原始钙钛矿具有相同晶格间距的混合卤化物钙钛矿。根据这些结果，我们确定了这些新晶相形成和溶解的动力学速率，并观察到晶体取向在光偏析和暗弛豫过程中得以保留。我们的结果与卤化物偏析模型一致，即激发导致混合自由能的变化，并最终在MAPb(IBr)相图中形成混溶间隙，这应为未来模拟和控制混合卤化物钙钛矿中卤化物偏析过程的工作提供参考。
