Understanding exciton formation is of fundamental importance for emerging optoelectronic materials, like hybrid organic–inorganic perovskites, as excitons are the lowest‐energy photoexcitations in semiconductors, are electrically neutral, and do not directly contribute to charge transport, but can emit light more efficiently than free carriers. However, despite the increasing attention toward these materials, experimental results on the processes of formation of an exciton population in perovskites are still elusive. Here, an ultrafast differential photoluminescence technique is presented that is able to track the kinetics of exciton formation and dissociation in CH₃NH₃PbBr₃. Data show the presence of geminate excitons, i.e., primary excitons directly created upon photon absorption, and their dissociation into free electron–hole pairs. The formation is demonstrated of a secondary exciton phase through pairing of the initial population of free carriers. The analysis of the generation of secondary excitons provides an estimate of the Langevin factor, the parameter governing the charge‐pairing rate. Understanding and controlling the formation of a bright exciton population instead of a highly conductive free carrier population may help to design new hybrid perovskite materials with tailored optoelectronic functionalities.

中文翻译：

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钙钛矿激子：主要激子的产生和从自由载体到次要激子相的过渡

了解激子的形成对于新兴的光电材料（例如混合的有机-无机钙钛矿）是至关重要的，因为激子是半导体中能量最低的光激发，是电中性的，不会直接促进电荷传输，但可以比发出的光更有效地发光。免费运营商。然而，尽管人们对这些材料的关注日益增加，但钙钛矿中激子种群形成过程的实验结果仍然难以捉摸。在这里，提出了一种超快速差分光致发光技术，该技术能够跟踪CH ₃ NH ₃ PbBr ₃中激子形成和解离的动力学。。数据表明存在双峰激子，即光子吸收后直接产生的初级激子，并解离成自由电子-空穴对。通过配对初始的自由载体，证明了次级激子相的形成。对次级激子生成的分析提供了兰格文因子的估计值，该参数决定着电荷配对速率。了解和控制明亮的激子种群而不是高导电自由载流子种群的形成可能有助于设计具有定制光电功能的新型混合钙钛矿材料。