Free Carrier Emergence and Onset of Electron-Phonon Coupling in Methylammonium Lead Halide Perovskite Films
Free Carrier Emergence and Onset of Electron-Phonon Coupling in Methylammonium Lead Halide Perovskite Films
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DOI：
10.1021/jacs.7b09508
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发表时间：
2017-12-20
影响因子：
15
通讯作者：
Ruhman, Sanford
中科院分区：
文献类型：
--
作者：
Ghosh, Tufan;Aharon, Sigalit;Ruhman, Sanford
描述了甲基铵卤化铅钙钛矿薄膜在10fs以下分辨率下的泵浦探针实验。光激发的初始响应分配给解离为自由载流子的局部热激子。这是由带积分的泵-探针光谱证明，其中光致漂白在光激发后20秒突然上升。后期的光谱演变与热载流子冷却一致，在此期间，状态填充引起带间和激子跃迁的漂白，奇怪的是，超过两倍。在两种薄膜的泵浦探测数据中观察到电子与光学声子的周期性光谱调制。傅里叶分析分别确定了与卤化铅框架和有机阳离子运动相关的100和300波数相似的活跃声子。从三种调制的深度估计的耦合强度处于弱耦合极限，与从温度相关的发射线形分析中提取的值一致。这些发现支持这些材料中的自由载流子以大极化子的形式存在。因此，这些模式可能不能决定该材料中载流子的适度迁移率。
Sub-10 fs resolution pump-probe experiments on methylammonium lead halide perovskite films are described. Initial response to photoexcitation is assigned to localized hot excitons which dissociate to free carriers. This is attested to by band integrals of the pump-probe spectra where photoinduced bleaching rises abruptly 20 fs after photoexcitation. Later stages of spectral evolution are consistent with hot carrier cooling, during which state filling induced bleaching of interband arid exciton transitions curiously, more, than doubles. Electron coupling to optical phonons is observed as periodic spectral modulations in the pump-probe data of both films. Fourier analysis identifies active phonons at similar to 100 and 300 wavenumbers pertaining to the lead-halide framework and organic cation motions, respectively. Coupling strengths estimated from the depth of thee modulations are in the weak coupling limit, in agreement with values extracted from temperature dependent emission line shape analysis. These findings support free carriers in these materials existing as large polarons. Accordingly, these modes are probably not dictating the moderate carrier mobility in this material.