Thouin Félix, Valverde-Chávez David A, Quarti Claudio, Cortecchia Daniele, Bargigia Ilaria, Beljonne David, Petrozza Annamaria, Silva Carlos, Srimath Kandada Ajay Ram
School of Physics, Georgia Institute of Technology, Atlanta, GA, USA.
School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, USA.
Nat Mater. 2019 Apr;18(4):349-356. doi: 10.1038/s41563-018-0262-7. Epub 2019 Jan 14.
Hybrid organic-inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the coexistence of diverse excitonic resonances, each with a distinct degree of polaronic character. By means of high-resolution resonant impulsive stimulated Raman spectroscopy, we identify vibrational wavepacket dynamics that evolve along different configurational coordinates for distinct excitons and photocarriers. Employing density functional theory calculations, we assign the observed coherent vibrational modes to various low-frequency (≲50 cm) optical phonons involving motion in the lead iodide layers. We thus conclude that different excitons induce specific lattice reorganizations, which are signatures of polaronic binding. This insight into the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials.
由于晶体的离子特性以及分子部分与无机网络之间非共价键产生的柔软性，有机-无机混合半导体具有复杂的晶格动力学。在此，我们证实，在典型的二维碘化铅钙钛矿中，这种动态结构复杂性导致了多种激子共振的共存，每种共振都具有不同程度的极化子特性。通过高分辨率共振脉冲受激拉曼光谱，我们识别出沿着不同构型坐标演化的振动波包动力学，这些坐标对应于不同的激子和光载流子。利用密度泛函理论计算，我们将观察到的相干振动模式归因于各种低频（≲50 cm）光学声子，这些声子涉及碘化铅层中的运动。因此，我们得出结论，不同的激子会引发特定的晶格重组，这是极化子结合的特征。这种对涉及全局中性初级光激发的能量/构型图景的洞察可能与更广泛的一类新兴混合半导体材料相关。
