Unfolding the role of local cation heterogeneities on the phase segregation and recovery in mixed-halide perovskites

Mixed-halide perovskites suffer from light-induced segregation, forming halide-rich domains with different bandgaps. Local techniques show local heterogeneities in the distribution of halides, which may lead to local strain that initiates halide segregation. It was found that the halide segregation kinetics also depend on the type of cation. Mixing cations reduces halide segregation but it remains unclear whether this is related to a relaxation of the strain. In this proposal, we will use time-resolved WAXS experiments to get insights on strain effects on phase segregation and recovery as function of cation composition. We will investigate the effect of pressure on the strain in mixed-cation perovskites, which was not reported before. Finally, although bulk techniques suggest full recovery of halide segregation, it is likely that some heterogeneities remain on local scale. Therefore, if the SAXS/WAXS is available, we will determine the local reversibility of halide segregation.

混合卤化物钙钛矿（mixed-halide perovskites）存在光诱导卤化物偏析问题，会形成具有不同带隙的富卤化物畴区。局域表征技术可揭示卤化物分布的局域异质性，此类异质性可能引发局部应变，进而诱发卤化物偏析。研究表明，卤化物偏析动力学还与阳离子种类密切相关。混合阳离子体系可缓解卤化物偏析，但目前尚不明确该效应是否与应变弛豫存在关联。在本研究方案中，我们将借助时间分辨广角X射线散射（WAXS）实验，探究应变对卤化物偏析与恢复过程的影响，以及该影响随阳离子组分的变化规律。我们还将研究压力对混合阳离子钙钛矿中应变的调控作用，该研究主题此前尚未见报道。最后，尽管宏观表征技术显示卤化物偏析可实现完全恢复，但局域尺度下仍可能残留部分异质性结构。因此，若可获取小角X射线散射（SAXS）/广角X射线散射（WAXS）测试数据，我们将进一步表征卤化物偏析的局域可逆性。