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Self-trapped excitons (STEs), proved to be the major source of white-light emission in two-dimensional (2D) metal halide perovskites (MHPs) van der Waals (vdW) heterostructures, have aroused intense interesting in photovoltaic and photoelectric applications. Nevertheless, the intrinsic mechanisms of STEs in these vdW heterostructures are still ambiguous. Here, we study the binding energy correction ∆EB of a self-trapped exciton stemming from the exciton-phonon coupling in MHPs vdW heterostructures based on the Pollmann-Büttner model. We find that there are two types of STEs with ∆EB > 0 and ∆EB < 0. The corresponding nuclear coordinate diagrams are given to explain the differences between them and why the STEs with ∆EB < 0 are hard to be observed in experiments. The phase transition between two types of STEs can be achieved by regulating the structural parameters, such as the vertical spacing between the encapsulation layers, the position of the monolayer MHP in the heterosturcture as well as replacing the encapsulation materials. The theoretical results provide important insights into the analysis and modulation of STEs in 2D vdW heterostructures.
I am a third-year graduate student majoring in theoretical Condensed Matter Physics in the School of Science, Tianjin University. My teacher is Professor Ziwu Wang. The main direction of research is self-trapped exciton (STE) states in metal halide perovskites (MHPs) van der Waals heterojunctions. In my main work, the Pollmann-Büttner model was derived in detail and a relatively accurate correction of an exciton ground-state binding energy owing to exciton-phonon coupling in two-dimensional (2D) materials is obtained. Based on the results of Pollmann-Büttner model and the phonon modes given by continuous dielectric model, we found two types of STE states in the 2D MHPs van der Waals heterostructure and provided insights for regulating the phase transition between them. Our results were published in Physica Status Solidi-Rapid Research Letter.
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