结构乱序对二维有机-无机杂化钙钛矿材料中激子行为和动力学的影响

本文合成了2-苯基乙基铵碘化铅(PEPI)和4-苯基-1-丁基铵碘化铅(PBPI)两种二维有机-无机杂化钙钛矿薄膜样品，并采用稳态吸收光谱、温度依赖的光致发光光谱和超快瞬态吸收光谱开展了细致的比较性研究. 由于含有较多的乙基基团，PBPI比PEPI具有更长的有机链，其无机骨架发生变形，从而引入结构乱序. 通过能域光谱线形和时域动力学的比较分析，揭示出PBPI中更大程度的结构乱序会导致更多缺陷态的形成，这些缺陷态可作为陷阱态以促进激子动力学. 另外，温度依赖的超快光谱揭示出激子共振的精细结构，并表明其与无机骨架而非有机链相关. 更进一步，在PEPI和PBPI中均观察到光激发相干声子，并揭示出结构乱序对无机骨架低频拉曼振动的微妙影响. 该工作为二维杂化钙钛矿材料的光学性质、激子行为和动力学以及相干声子效应提供了有益的见解.

Impact of Structural Disorder on Excitonic Behaviors and Dynamics in 2D Organic-Inorganic Hybrid Perovskites

Two thin-film 2D organic-inorganic hybrid perovskites, i.e., 2-phenylethylammonium lead iodide (PEPI) and 4-phenyl-1-butylammonium lead iodide (PBPI) were synthesized and investigated by steady-state absorption, temperature-dependent photoluminescence, and temperature-dependent ultrafast transient absorption spectroscopy. PBPI has a longer organic chain (via introducing extra ethyl groups) than PEPI, thus its inorganic skeleton can be distorted, bringing on structural disorder. The comparative analyses of spectral pro-files and temporal dynamics revealed that the greater structural disorder in PBPI results in more defect states serving as trap states to promote exciton dynamics. In addition, the fine-structuring of excitonic resonances was unveiled by temperature-dependent ultrafast spectroscopy, suggesting its correlation with inorganic skeleton rather than organic chain. Moreover, the photoexcited coherent phonons were observed in both PEPI and PBPI, pointing to a subtle impact of structural disorder on the low-frequency Raman-active vibrations of inorganic skeleton. This work provides valuable insights into the optical properties, excitonic behaviors and dynamics, as well as coherent phonon effects in 2D hybrid perovskites.