Terahertz Emission from Hybrid Perovskites Driven by Ultrafast Charge Separation and Strong Electron-Phonon Coupling
Terahertz Emission from Hybrid Perovskites Driven by Ultrafast Charge Separation and Strong Electron-Phonon Coupling
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DOI：
10.1002/adma.201704737
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发表时间：
2018-03-15
影响因子：
29.4
通讯作者：
Lindenberg, Aaron M.
中科院分区：
文献类型：
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作者：
Guzelturk, Burak;Belisle, Rebecca A.;Lindenberg, Aaron M.
有机-无机杂化钙钛矿的不寻常的电物理性质不仅使光电器件具有优异的性能，而且还导致了对这些材料中电荷载流子性质的争论。本研究首次观察到混合钙钛矿甲基铵碘化铅（CH3NH3PbI3）在光激发后的强烈太赫兹（THz）发射，从而能够在1个太阳等效照明条件下实现电荷分离，热载流子传输和载流子晶格耦合的超快探测。使用这种方法，在混合钙钛矿中的初始电荷分离/运输被证明是由扩散驱动，而不是由表面场或固有的铁电性。热载流子和带边载流子沿着表面法线方向的扩散系数通过分析发射的太赫兹瞬态计算，与热载流子器件应用的直接影响。此外，光生载流子被发现驱动相干太赫兹频率晶格畸变，与碘化铅八面体的重组以及有机和无机亚晶格的耦合振动。这种强大的和相干的载体晶格耦合飞秒时间尺度上解决，并发现是重要的共振和远高于间隙光激发。这项研究表明，超快晶格畸变在与电荷输运相关的初始过程中起着关键作用。
Unusual photophysical properties of organic-inorganic hybrid perovskites have not only enabled exceptional performance in optoelectronic devices, but also led to debates on the nature of charge carriers in these materials. This study makes the first observation of intense terahertz (THz) emission from the hybrid perovskite methylammonium lead iodide (CH3NH3PbI3) following photoexcitation, enabling an ultrafast probe of charge separation, hot-carrier transport, and carrier-lattice coupling under 1-sun-equivalent illumination conditions. Using this approach, the initial charge separation/transport in the hybrid perovskites is shown to be driven by diffusion and not by surface fields or intrinsic ferroelectricity. Diffusivities of the hot and band-edge carriers along the surface normal direction are calculated by analyzing the emitted THz transients, with direct implications for hot-carrier device applications. Furthermore, photogenerated carriers are found to drive coherent terahertz-frequency lattice distortions, associated with reorganizations of the lead-iodide octahedra as well as coupled vibrations of the organic and inorganic sublattices. This strong and coherent carrier-lattice coupling is resolved on femtosecond timescales and found to be important both for resonant and far-above-gap photoexcitation. This study indicates that ultrafast lattice distortions play a key role in the initial processes associated with charge transport.