Probing femtosecond lattice displacement upon photo-carrier generation in lead halide perovskite.
Probing femtosecond lattice displacement upon photo-carrier generation in lead halide perovskite.
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DOI：
10.1038/s41467-018-04367-6
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发表时间：
2018-05-17
影响因子：
16.6
通讯作者：
Scopigno T
中科院分区：
文献类型：
--
作者：
Batignani G;Fumero G;Srimath Kandada AR;Cerullo G;Gandini M;Ferrante C;Petrozza A;Scopigno T
由于其晶格的软波动性质，预期金属卤化物钙钛矿中的电子性质和晶格振动强烈相关。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，以揭示在电子共振和非共振条件下的甲基铵溴化铅钙钛矿的振动模式。我们在89和106 cm−1处识别出两个激发态相干声子，其相位揭示了超快光生载流子产生时势能最小值的偏移。这表明过渡到一个新的几何形状，达到约90 fs后，完全平衡的声子寿命约1 ps。我们的研究结果明确地证明，这些模式驱动光激发时发生的晶体畸变，证明极化效应的存在。电子-声子耦合是理解卤化铅钙钛矿材料光电性质的关键，但对其进行探测是一个难点。在这里，Batignani等人用脉冲振动光谱观察到两种新的声子模式，为光激发的极化性质提供了证据。
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−1, 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. The electron–phonon coupling is the key to understand optoelectronic properties in lead halide perovskites but it is difficult to probe. Here Batignani et al. observe two new phonon modes with impulsive vibrational spectroscopy providing the evidence of the polaronic nature of the photo-excitation.
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