Unraveling Exciton Trap Dynamics and Nonradiative Loss Pathways in Quantum Dots via Atomistic Simulations

TL;DR

This study uses atomistic simulations to elucidate how surface defects in quantum dots cause exciton trapping and nonradiative losses, revealing the microscopic mechanisms and potential avenues for improving QD efficiency.

Contribution

The paper introduces a detailed atomistic model to analyze exciton dynamics and defect-induced nonradiative pathways in quantum dots, providing new insights into defect effects.

Findings

Single defect induces multiple excitonic states and relaxation regimes.

Defect properties influence the balance between radiative and nonradiative decay.

Polaron shifts and exciton-phonon couplings are key to exciton dynamics.

Abstract

Surface defects in colloidal quantum dots are a major source of nonradiative losses, yet the microscopic mechanisms underlying exciton trapping and recombination remain elusive. Here, we develop a model Hamiltonian based on atomistic electronic calculations to investigate exciton dynamics in CdSe/CdS core/shell QDs containing a single hole trap introduced by an unpassivated sulfur atom. By systematically varying the defect depth and reorganization energy, we uncover how defect-induced excitonic states mediate energy relaxation pathways. Our simulations reveal that a single localized defect can induce a rich spectrum of excitonic states, leading to multiple dynamical regimes, from slow, energetically off-resonant trapping to fast, cascaded relaxation through in-gap defect states. Crucially, we quantify how defect-induced polaron shifts and exciton-phonon couplings govern the balance between efficient radiative emission and rapid nonradiative decay. These insights clarify the microscopic origin of defect-assisted loss channels and suggest pathways for tailoring QD optoelectronic properties via surface and defect engineering.