Abstract:

Molecular dynamics simulation is used to investigate the structure characteristics and mechanical properties, and to discuss the vapor deposition of MAPbI₃ on the TiO₂ substrate under a temperature of 300 K and three precursor compositions of PbI₂:CH₃NH₃I=1:2, 1:1 and 2:1, respectively. During the preparation processes, three polyhedral groups including PbI₄^2- tetrahedra, PbI₅^3- pyramids and PbI₆^4- octahedra are produced. After classifying their arrangements and analyzing the distribution of CH₃NH₃⁺ cations, early CH₃NH₃PbI₃ nuclei consisting of well-connected PbI_x (x=4, 5 or 6) polyhedral clusters and sufficient amounts of surrounding CH₃NH₃⁺ cations were identified. The influence on early nuclei from the precursor compositions of PbI₂:CH₃NH₃I were discussed. The results show that the calculated values of elastic modulus is in good agreement with the experimental results. The PbI₅^3- pyramids dominate over other polyhedral groups during the vapor deposition simulations. Meanwhile, even though the total amounts of polyhedra have a small dependence on the precursor compositions, the populations of the well-connected clusters and the early nuclei decrease rapidly with increasing the PbI₂:CH₃NH₃I ratio. This is in consistent with the experimental finding which to some degree, adding more CH₃NH₃I will optimize the device performance.

Key words: hybrid perovskite, molecular simulation, crystallization, precursor composition, solar energy, vapor deposition

摘要：

应用分子动力学方法分析了甲胺铅碘晶体的结构特征与机械性质等相关物性，模拟了用蒸气沉积法在TiO₂基底上制备甲胺铅碘晶体的过程，探讨了生成的PbI₄^2-、PbI₅^3-和PbI₄^6-多面体的排布方式，结合周围CH₃NH₃⁺的分布筛选出满足结构要求的初生晶核，分析了前驱盐配比对甲胺铅碘初生晶核产量的影响。结果表明，在拉伸过程中，甲胺铅碘晶体经历弹性形变、塑性形变以及断裂三个阶段，拟合计算得到的弹性模量与实验值符合较好；大部分初生晶核以PbI₅^3-金字塔的结构存在。前驱盐配比对各系统中PbI_x多面体的总含量影响较小，但对其中排布有效的PbI_x结构以及初生晶核的产量影响较大，二者产量随着配比PbI₂∶CH₃NH₃I的增加而迅速减小，这一关系与研究者发现的实验现象相符。

关键词: 杂化钙钛矿, 分子模拟, 结晶, 前驱盐配比, 太阳能, 蒸气沉积法