Exciton diffusion from first principles: role of crystal packing and composition

Understanding excited-state dynamics in functional materials is essential for applications across optoelectronics and photophysics. In particular, exciton diffusion and relaxation mechanisms are coupled to optical selection rules and can be tuned through atomistic design. In this talk, I will present our recent studies of exciton transport in functional materials, using ab initio computations based on many-body perturbation theory. Specifically, I will discuss the relation between exciton relaxation mechanisms with the underlying material structure and symmetry: molecular packing in organic crystals and defect and heterostructure design in transition metal dichalcogenides. I will present our new approach to compute exciton propagation, in which non-analytical discontinuities in the exciton dispersion are connected to the early stages of exciton diffusion. I will further discuss our scheme to include exciton-phonon interactions from first principles and the associated exciton diffusion lifetimes and pathways.