The coupling between the polar lattice and the electronic system is a key ingredient enabling the impressive properties of 2D and 3D metal-halide perovskites (MHPs). For example, mechanisms such as polaron formation and edge states have been proposed to explain efficient exciton dissociation observed in 2D MHPs. However, neither mechanism has been directly validated. By analyzing the temperature dependence of the exciton’s linear and quadratic Stark shifts, this study reveals another important aspect of charge–lattice interactions. We find excitons are photoexcited into spatially separated states and possess large dipole moments and, thus, have significant charge-transfer character. The dipole moments are induced by thermal fluctuations in the polar lattice. Molecular dynamics simulations, which agree closely with our experiments in predicting the measured dipole moments, also predict that these thermal fluctuations could be sufficient to ionize the electron–hole system.

中文翻译：

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二维金属卤化物钙钛矿中的随机电荷转移激子

极性晶格和电子系统之间的耦合是实现 2D 和 3D 金属卤化物钙钛矿 (MHP) 令人印象深刻的特性的关键因素。例如，人们提出了极化子形成和边缘态等机制来解释二维 MHP 中观察到的有效激子解离。然而，这两种机制都没有得到直接验证。通过分析激子线性和二次斯塔克位移的温度依赖性，这项研究揭示了电荷-晶格相互作用的另一个重要方面。我们发现激子被光激发成空间分离的状态并具有大的偶极矩，因此具有显着的电荷转移特性。偶极矩是由极晶格中的热波动引起的。分子动力学模拟与我们预测测量偶极矩的实验非常吻合，也预测这些热波动可能足以电离电子空穴系统。