Halogen Effects on Ordering and Bonding of CH3NH3+ in CH3NH3PbX3 (X = Cl, Br, I) Hybrid Perovskites: A Vibrational Spectroscopic Study
Halogen Effects on Ordering and Bonding of CH3NH3+ in CH3NH3PbX3 (X = Cl, Br, I) Hybrid Perovskites: A Vibrational Spectroscopic Study
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DOI：
10.1021/acs.jpcc.5b11256
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发表时间：
2016-02-11
影响因子：
3.7
通讯作者：
Cameron, Petra J.
中科院分区：
文献类型：
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作者：
Niemann, Ralf G.;Kontos, Athanassios G.;Cameron, Petra J.
本文报道了有机-无机杂化MAPbX（3）钙钛矿（MA = CH_3 NH_3，X = Cl，Br，I）及其混合卤化物衍生物的拉曼和红外光谱。拉曼光谱记录在三个激光波长（514，785，和1064 nm）在开和关共振条件下，以及在室温和100 K。使用不同的激发波长允许从钙钛矿明确地获取“真实”拉曼光谱，而没有退化或光致结构变化。通过比较拉曼光谱和远红外光谱的结果，我们完全确定了PbX的低频振动模式。红色拉曼频移几乎所有的MA振动从200至3200 cm（-1），特别是强烈的扭转模式，观察到重卤化物衍生物，加强卤化物和无机笼内的有机阳离子之间的相互作用的指示。不同的MA-X键合方案证明出现在正交相的扭转模式对。通过变温拉曼测量（100-295 K）进一步表征MAPbBr（3）。MA摇摆模式略高于tetratetrachiI到II相变的加宽与MA阳离子的无序有关。我们的研究结果推进理解钙钛矿材料的性能（铁电畴的形成，异常滞后）和它们的使用作为有效的光吸收剂在太阳能电池。
This study reports Raman and infrared spectra of hybrid organic-inorganic MAPbX(3) perovskites (MA = CH3NH3, X = Cl, Br, I) and their mixed-halide derivatives. Raman spectra were recorded at three laser wavelengths (514, 785, and 1064 nm) under on- and off-resonance conditions, as well as at room temperature and 100 K. The use of different excitation wavelengths allowed the unambiguous acquisition of "true" Raman spectra from the perovskites, without degradation or photoinduced structural changes. Low-frequency PbX vibrational modes were thoroughly identified by comparison of Raman and far-IR results. Red Raman frequency shifts for almost all MA vibrations from 200 to 3200 cm(-1), and particularly intense for the torsional mode, were observed toward heavy halide derivatives, indicative of strengthening the interaction between halides and the organic cation inside the inorganic cage. Different MA-X bonding schemes are evidenced by torsional mode pairs emerging in the orthorhombic phase. MAPbBr(3) was further characterized by variable temperature Raman measurements (100-295 K). Broadening of the MA rocking mode slightly above the tetragonal I to II phase transition is connected with disorder of the MA cation. Our results advance the understanding of perovirsite materials properties (ferroelectric domain formation, anomalous hysteresis) and their use as efficient light absorbers in solar cells.