Dynamics of photoexcited Janus semiconductor nanocrystals: DFT-based calculation

Applications of heterostructured nanomaterials, such as Janus semiconductor nanocrystals (NCs), require a quantitative understanding of their photoexcited properties. Here, we study photoexcited state time evolution of a reference PbSe NC and several 1.9 nm Janus NCs made of Cd, Pb, and Se by employing the Boltzmann transport equation (BE), which allows for competition between different relaxation channels such as phonon-mediated carrier thermalization, exciton transfer, and exciton multiplication and recombination. BE collision integrals (CI) are computed using finite-temperature many-body perturbation theory (sometimes called Kadanoff-Baym-Keldysh (KBK) technique) based on density functional theory (DFT) simulations. Exciton effects are included by solving the Bethe-Salpeter equation, with additional simplifying approximations, and incorporating exciton energies and states into the CI. Phonon-mediated relaxation is included by utilizing on-the-fly nonadiabatic coupling data from DFT-based finite-temperature molecular dynamics simulations in the KBK technique. In particular, we calculate internal quantum efficiency (the number of excitons generated from a single absorbed energetic photon) and discuss the formation of charge transfer states in the Janus and uniform systems.