Colloidal quantum dots (QDs) have been heavily investigated due to their potential promise in applications ranging from display technology to bio-imaging and solar energy conversion. Covering the inner part of the QD, a core, by a shell made from large-bandgap semiconductor reduces the environment impact and improves QD’s optical properties. Additionally, the chemical composition of the core and shell in such core/shell QDs allows for manipulations of the photoexcited processes such as energy relaxation via phonons and multi carrier generation from a single adsorbed photon. We computationally investigate how chemical composition influences the relaxation rates of the photoexcited electron/hole pair in (PbX)16/(CdX)52, (X = S, Se) core/shell QDs. This is accomplished applying time-domain non-adiabatic dynamics based on density functional theory and coupled to the Fewest Switches Surface Hopping technique. Although the ground state electronic properties and phonon spectra are similar in these systems, the relaxation rate for PbSe/CdSe Ds is twice slower compared to PbS/CdS. The long-lived excitation in PbSe/CdSe QDs is associated to nearly twice weaker non-adiabatic electron-phonon couplings, compared to PbS/CdS QDs. In both structures, the lower-energy acoustic phonons originated from the Pb-Se interface have the largest contributions to the couplings with high-energy excitons, while optical phonons of the core have much more significant contributions only in PbS/CdS QDs. The slow energy relaxation in PbSe/CdSe creates favorable conditions for multi-exciton generation in these systems, rather than in PbS/CdS QDs.

Influence of chemical composition on relaxation rates of electron/hole pair in (PbX)16/(CdX)52, (X = S, Se) core/shell quantum dots

256th National Meeting (2018)

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