Dynamics of dissipative multiple exciton generation in nanocrystals

TL;DR

This paper models the population dynamics of exciton states in semiconductor nanocrystals, revealing how dissipation influences the growth and decay of bi-excitons, with implications for optimizing multiple exciton generation.

Contribution

It introduces a numerical model that incorporates Coulomb coupling and dissipation to study exciton dynamics, highlighting the effects on bi-exciton populations and ensemble behavior.

Findings

Dissipation significantly alters exciton population dynamics.

Fast MEG process occurs on picosecond timescale.

Maximum bi-exciton occupation can increase with dissipation.

Abstract

The population dynamics of single- and bi-exciton states in semiconductor nanocrystals is modeled numerically in the presence of Coulomb coupling between single- and two-exciton states and a dissipation channel in order to study the transient bi-exciton population that occurs in an optically excited semiconductor nanocrystal. The results show that the system evolution strongly changes if the dissipation is included. In a certain range of parameters, the growth of the exciton number (MEG process) is fast (on picosecond time scale) and the following decay (Auger process) is much slower (hundreds of picoseconds). In some cases, the maximum occupation of the bi-exciton state increases when dissipation is included. The dynamics of an ensemble of nanocrystals with a certain size dispersion is studied by averaging over the energy of the bi-exciton state which can be different for each single nanocrystal. The validity of Markov and secular approximation is also verified.