Zhu Xiangzhou, Caicedo-Dávila Sebastián, Gehrmann Christian, Egger David A
Department of Physics, Technical University of Munich, James-Franck-Strasse 1, 85748 Garching, Germany.
ACS Appl Mater Interfaces. 2022 Apr 21. doi: 10.1021/acsami.1c23099.
Strong deviations in the finite temperature atomic structure of halide perovskites from their average geometry can have profound impacts on optoelectronic and other device-relevant properties. Detailed mechanistic understandings of these structural fluctuations and their consequences remain, however, limited by the experimental and theoretical challenges involved in characterizing strongly anharmonic vibrational characteristics and their impact on other properties. We overcome some of these challenges by a theoretical characterization of the vibrational interactions that occur among the atoms in the prototypical cubic CsPbBr. Our investigation based on first-principles molecular dynamics calculations finds that the motions of neighboring Cs-Br atoms interlock, which appears as the most likely Cs-Br distance being significantly shorter than what is inferred from an ideal cubic structure. This form of dynamic Cs-Br coupling coincides with very shallow dynamic potential wells for Br motions that occur across a locally and dynamically disordered energy landscape. We reveal an interesting dynamic coupling mechanism among the atoms within the nominal unit cell of cubic CsPbBr and quantify the important local structural fluctuations on an atomic scale.
卤化物钙钛矿在有限温度下的原子结构与其平均几何结构存在强烈偏差，这可能对光电及其他与器件相关的性能产生深远影响。然而，由于表征强非谐振动特性及其对其他性能的影响所涉及的实验和理论挑战，对这些结构波动及其后果的详细机理理解仍然有限。我们通过对典型立方CsPbBr中原子间发生的振动相互作用进行理论表征，克服了其中一些挑战。我们基于第一性原理分子动力学计算的研究发现，相邻Cs-Br原子的运动相互连锁，这表现为最可能的Cs-Br距离明显短于从理想立方结构推断出的距离。这种动态Cs-Br耦合形式与Br在局部和动态无序能量景观中运动时非常浅的动态势阱相吻合。我们揭示了立方CsPbBr名义晶胞内原子间一种有趣的动态耦合机制，并在原子尺度上量化了重要的局部结构波动。
