Solution-processable metal halide perovskites (MHPs) offer great promise for efficient light-harvesting and -emitting devices because of their long carrier lifetime and superior carrier transport properties. Similar to traditional oxide perovskites, MHPs exhibit strong dynamic disorders that may further impact their electronic properties. Here we investigate the coherent acoustic phonons of inorganic and organic–inorganic (hybrid) MHP single crystals (CsPbCl₃, MAPbCl₃, CsPbBr₃, MAPbBr₃, FAPbBr₃, MAPbI₃, and FAPbI₃) using pump–probe reflection spectroscopy. We show significant phonon softening in the cubic phase of all compositions close to the cubic-to-tetragonal phase transition temperature. Such phonon softening in conjunction with strong acoustic damping is attributed to pretransitional polar fluctuations. Comparison of MHPs with different compositions show that the degree of pretransitional fluctuations is correlated with the size rather than the dipole moment of the A-site cations, and further with the size of the anions.

中文翻译：

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声子异常发现的金属卤化物钙钛矿中的极性涨落

溶液可加工的金属卤化物钙钛矿（MHP）由于其较长的载流子寿命和优异的载流子传输性能，为高效的光收集和发射设备提供了广阔前景。与传统的钙钛矿氧化物相似，MHP表现出强烈的动态紊乱，可能进一步影响其电子性能。在这里，我们研究了无机和有机-无机（混合）MHP单晶（CsPbCl ₃，MAPbCl ₃，CsPbBr ₃，MAPbBr ₃，FAPbBr ₃，MAPbI ₃和FAPbI ₃）的相干声子），使用泵浦-探针反射光谱法。我们显示，在接近立方到四方相变温度的所有组成的立方相中，声子都有明显的声子软化。这种声子软化结合强的声阻尼归因于过渡前的极性波动。具有不同组成的MHP的比较表明，过渡前起伏的程度与A位阳离子的大小而不是偶极矩有关，并且与阴离子的大小有关。