The role of dipolar motion of organic cations in the A-sites of halide perovskites has been debated in an effort to understand why these materials possess such remarkable properties. Here, we show that the dipolar motion of cations such as methylammonium (MA) or formamidinium (FA) versus cesium (Cs) does not influence large polaron binding energies, delocalization lengths, formation times, or bimolecular recombination lifetimes in lead bromide perovskites containing only one type of A-site cation. We directly probe the transient absorption spectra of large polarons throughout the entire mid-infrared and resolve their dynamics on time scales from sub-100 fs to sub-μs using time-resolved mid-infrared spectroscopy. Our findings suggest that the improved optoelectronic properties reported of halide perovskites with mixed A-site cations may result from synergy among the cations and how their mixture modulates the structure and dynamics of the inorganic lattice rather than from the dipolar properties of the cations themselves.

中文翻译：

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有机阳离子的偶极运动是否会影响卤化物钙钛矿中的极化子动力学和双分子复合？

为了理解为什么这些材料具有如此卓越的性能，人们一直在争论有机阳离子在偶极卤化物钙钛矿的A-位中的作用。在这里，我们表明阳离子（例如甲基铵（MA）或甲ami（FA）与铯（Cs））的偶极运动不会影响仅含溴化钙钛矿的大极化子结合能，离域长度，形成时间或双分子重组寿命。一种A位阳离子。我们直接探测整个极化过程中大极化子的瞬态吸收光谱，并使用时间分辨的中红外光谱法在从100 fs到亚μs的时间尺度上解析其动力学。