Computational Investigation of Charge Localization and Structural Dynamics in Halide Perovskites

Licentiate thesis, 2025

Halide perovskites have gained significant interest due to their remarkable optoelectronic properties and diverse applications. However, most of these applications involve lead-based halide perovskites which suffer from critical challenges related to lead toxicity and long-term stability. In order to counter these challenges various strategies have been explored, including encapsulation, surface passivation, compositional engineering, and alternative synthesis techniques. One of the promising approaches is the development of lead-free halide perovskites. In this licentiate thesis, a computational study is conducted on these materials, using advanced Density Functional Theory calculations and Molecular Dynamics simulations employing neuroevolution potentials. The structural properties, with a particular focus on octahedral tilting and phase transitions are explored. Furthermore, charge localizations in the form of polarons in Cs2AgBiBr6 and CsGeX3 (X=Cl,Br,I) are investigated. Additionally, the formation of self-trapped excitons in Cs2AgBiBr6 is  examined. These self-trapped states play an important role in the material optical properties reported in several experimental reports. Overall, the results in this work provide valuable insights on the structural and electronic properties of lead-free halide perovskites.