Ghosh Dibyajyoti, Aziz Alex, Dawson James A, Walker Alison B, Islam M Saiful
Department of Physics and Department of Chemistry, University of Bath, Bath BA2 7AY, U.K.
Chem Mater. 2019 Jun 11;31(11):4063-4071. doi: 10.1021/acs.chemmater.9b00648. Epub 2019 May 14.
Lattice compression through hydrostatic pressure has emerged as an effective means of tuning the structural and optoelectronic properties of hybrid halide perovskites. In addition to external pressure, the local strain present in solution-processed thin films also causes significant heterogeneity in their photophysical properties. However, an atomistic understanding of structural changes of hybrid perovskites under pressure and their effects on the electronic landscape is required. Here, we use high level simulation techniques to explore the effect of lattice compression on the formamidinium (FA) lead iodide compound, FA Cs PbI ( = 0, 0.25). We show that, in response to applied pressure, the Pb-I bonds shorten, the PbI octahedra tilt anisotropically, and the rotational dynamics of the FA molecular cation are partially suppressed. Because of these structural distortions, the compressed perovskites exhibit band gaps that are narrower (red-shifted) and indirect with spin-split band edges. Furthermore, the shallow defect levels of intrinsic iodide defects transform to deep-level states with lattice compression. This work highlights the use of hydrostatic pressure as a powerful tool for systematically modifying the photovoltaic performance of halide perovskites.
通过静水压力实现的晶格压缩已成为调节杂化卤化物钙钛矿结构和光电性质的有效手段。除了外部压力外，溶液处理薄膜中存在的局部应变也会导致其光物理性质出现显著的不均匀性。然而，需要从原子层面理解杂化钙钛矿在压力下的结构变化及其对电子态的影响。在此，我们使用高级模拟技术来探究晶格压缩对甲脒（FA）碘化铅化合物FAₓCs₁₋ₓPbI₃（x = 0, 0.25）的影响。我们表明，在施加压力时，Pb - I键缩短，PbI₆八面体发生各向异性倾斜，并且FA分子阳离子的旋转动力学受到部分抑制。由于这些结构畸变，压缩后的钙钛矿呈现出更窄（红移）且具有自旋分裂带边的间接带隙。此外，本征碘化物缺陷的浅缺陷能级随着晶格压缩转变为深能级状态。这项工作突出了静水压力作为一种强大工具用于系统地调节卤化物钙钛矿光伏性能的作用。
