Srivastava Pradhi, Maity Sayan, Srinivasan Varadharajan
Department of Physics, Indian Institute of Science Education and Research Bhopal, Bhopal, 462066, India.
Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal, 462 066, India.
Small. 2025 Mar;21(10):e2404493. doi: 10.1002/smll.202404493. Epub 2025 Jan 14.
The structural and electronic changes are investigated in a 3D hybrid perovskite, methylhydrazinium lead chloride (MHyPbCl) from a host/guest perspective as it transitions from a highly polar to less polar phase upon cooling, using first-principles calculations. The two phases vary structurally in the guest (MHy) orientation and the two differently distorted host (lead halide) layers. These findings highlight the critical role of guest reorientation in reducing host distortion at high temperatures, making the former the primary order parameter for the transition, a notable contrast to the case of other hybrid perovskites. This is also confirmed by the dominating contribution of guest reorientation along the transition pathway. Analysis using maximally localized Wannier functions reveals that polarization enhancement upon heating is primarily due to host atoms, particularly of the more distorted octahedral layer. Despite its pivotal role in the transition, the contribution of the guest to polarization is relatively weaker, in contrast to previous suggestions. Furthermore, host distortion induces a significant (∼9%) feedback polarization on the guest. This distortion is also responsible for significantly altering the density of states occupied by the guest closer to band-edges, suggesting a non-trivial contribution of the guest in impacting the optoelectronic properties and exciton binding energies.
利用第一性原理计算，从主体/客体的角度研究了三维混合钙钛矿甲基肼氯化铅（MHyPbCl）在冷却时从高极性相转变为低极性相过程中的结构和电子变化。这两个相在客体（MHy）取向以及两个不同畸变的主体（卤化铅）层的结构上有所不同。这些发现突出了客体重新取向在高温下减少主体畸变中的关键作用，使得客体重新取向成为转变的主要序参量，这与其他混合钙钛矿的情况形成显著对比。沿着转变路径的客体重新取向的主导贡献也证实了这一点。使用最大局域化万尼尔函数的分析表明，加热时的极化增强主要归因于主体原子，特别是畸变更严重的八面体层的原子。尽管客体在转变中起关键作用，但与之前的观点相反，客体对极化的贡献相对较弱。此外，主体畸变在客体上诱导出显著的（约9%）反馈极化。这种畸变还导致靠近带边的客体占据态密度发生显著变化，表明客体在影响光电性质和激子结合能方面有重要贡献。
