Department of Applied Physics and Materials Science, California Institute of Technology, Pasadena, CA, 91125, USA.
School of Physics, Trinity College Dublin, Dublin 2, Ireland.
Nat Commun. 2018 May 8;9(1):1829. doi: 10.1038/s41467-018-04212-w.
Methylammonium lead iodide perovskite (MAPbI) exhibits long charge carrier lifetimes that are linked to its high efficiency in solar cells. Yet, the mechanisms governing these unusual carrier dynamics are not completely understood. A leading hypothesis-disproved in this work-is that a large, static bulk Rashba effect slows down carrier recombination. Here, using second harmonic generation rotational anisotropy measurements on MAPbI crystals, we demonstrate that the bulk structure of tetragonal MAPbI is centrosymmetric with I4/mcm space group. Our calculations show that a significant Rashba splitting in the bandstructure requires a non-centrosymmetric lead iodide framework, and that incorrect structural relaxations are responsible for the previously predicted large Rashba effect. The small Rashba splitting allows us to compute effective masses in excellent agreement with experiment. Our findings rule out the presence of a large static Rashba effect in bulk MAPbI, and our measurements find no evidence of dynamic Rashba effects.
甲脒碘化铅钙钛矿（MAPbI）具有长电荷载流子寿命，这与其在太阳能电池中的高效率有关。然而，控制这些异常载流子动力学的机制尚未完全理解。一个主要的假设——在这项工作中被否定——是一个大的、静态的体 Rashba 效应会减缓载流子复合。在这里，我们使用 MAPbI 晶体的二次谐波产生旋转各向异性测量，证明了四方 MAPbI 的体结构是具有 I4/mcm 空间群的中心对称。我们的计算表明，能带结构中显著的 Rashba 劈裂需要一个非中心对称的碘化铅框架，而不正确的结构弛豫是导致先前预测的大 Rashba 效应的原因。小的 Rashba 劈裂允许我们计算出与实验非常吻合的有效质量。我们的发现排除了在体 MAPbI 中存在大的静态 Rashba 效应的可能性，我们的测量也没有发现动态 Rashba 效应的证据。
