Dipartimento di Fisica, Università di Roma "La Sapienza", Roma, I-00185, Italy.
Dipartimento di Scienze di Base e Applicate per l'Ingegneria, Università di Roma "La Sapienza", Roma, I-00185, Italy.
Nat Commun. 2018 May 17;9(1):1971. doi: 10.1038/s41467-018-04367-6.
Electronic properties and lattice vibrations are expected to be strongly correlated in metal-halide perovskites, due to the soft fluctuating nature of their crystal lattice. Thus, unveiling electron-phonon coupling dynamics upon ultrafast photoexcitation is necessary for understanding the optoelectronic behavior of the semiconductor. Here, we use impulsive vibrational spectroscopy to reveal vibrational modes of methylammonium lead-bromide perovskite under electronically resonant and non-resonant conditions. We identify two excited state coherent phonons at 89 and 106 cm, whose phases reveal a shift of the potential energy minimum upon ultrafast photocarrier generation. This indicates the transition to a new geometry, reached after approximately 90 fs, and fully equilibrated within the phonons lifetime of about 1 ps. Our results unambiguously prove that these modes drive the crystalline distortion occurring upon photo-excitation, demonstrating the presence of polaronic effects.
电子特性和晶格振动有望在金属卤化物钙钛矿中存在强烈的相关性，这是由于其晶格具有柔软且易波动的特性。因此，揭示超快光激发下的电子-声子耦合动力学对于理解半导体的光电行为是必要的。在这里，我们使用脉冲振动光谱在电子共振和非共振条件下揭示了甲脒碘化铅钙钛矿的振动模式。我们在 89 和 106cm 处识别出两个激发态相干声子，它们的相位表明超快光生载流子生成时势能最小值发生了位移。这表明在大约 90fs 后会发生到新的几何形状的转变，并在大约 1ps 的声子寿命内完全达到平衡。我们的结果明确证明了这些模式驱动了光激发下发生的晶体变形，证明了极化子效应的存在。
