Excitons in Low-Dimensional Metal-Halide Perovskites from First-Principles Calculations

Excitons, neutral quasiparticles formed by electron-hole pairs, play a key role in the optoelectronic properties of semiconductors. Understanding their formation, transport, and dissociation is essential for interpreting experiments, predicting material behavior, and designing new materials for targeted applications. Low-dimensional halide perovskite semiconductors provide a versatile platform for studying excitons due to their structural tunability and ease of fabrication. Quasi-two-dimensional (2D) halide perovskites, consisting of metal-halide octahedral layers separated by organic spacers, are particularly promising. Their unique structure, which disrupts octahedral connectivity in one direction, results in anisotropic charge-carrier masses and dielectric screening, promoting the formation of strongly bound excitons.

First-principles calculations of excitonic properties in these materials have been limited by the large unit-cell sizes of most experimentally synthesized quasi-2D perovskites. However, recent advances in hardware and many-body perturbation theory methods, such as the GW and Bethe-Salpeter Equation approaches, now enable detailed insights into these systems. In this presentation, I will showcase how these calculations provide a microscopic understanding of the experimentally observed polarization dependence of intra-, interlayer and charge-transfer excitons. Additionally, I will discuss the influence of chemical composition, layer spacing, and stacking on excitonic behavior, shedding light on possibilities for tuning the optoelectronic properties of these complex semiconductors. These insights lay the groundwork for advancing the design of next-generation optoelectronic devices, leveraging the unique excitonic properties of low-dimensional perovskites.