Time Dependent Study of Multiple Exciton Generation in Nanocrystal Quantum Dots

TL;DR

This study investigates the dynamics of multiple exciton generation in nanocrystal quantum dots, revealing how excitation parameters influence efficiency and demonstrating results consistent with experimental quantum yields.

Contribution

It provides a detailed quantum rate equation model for exciton dynamics in nanocrystals, incorporating many-particle states and impact ionization processes, which advances understanding of exciton generation efficiency.

Findings

Quantum yield comparable to experimental values for PbS quantum dots.

Impact ionization facilitates transfer from single to double excitons.

Excitation parameters significantly affect multiple exciton formation.

Abstract

We study the exciton dynamics in an optically excited nanocrystal quantum dot. Multiple exciton formation is more efficient in nanocrystal quantum dots compared to bulk semiconductors due to enhanced Coulomb interactions and the absence of conservation of momentum. The formation of multiple excitons is dependent on different excitation parameters and the dissipation. We study this process within a Lindblad quantum rate equation using the full many-particle states. We optically excite the system by creating a single high energy exciton $E_{SX}$ in resonance to a double exciton $E_{DX}$. With Coulomb electron-electron interaction, the population can be transferred from the single exciton to the double exciton state by impact ionisation (inverse Auger process). The ratio between the recombination processes and the absorbed photons provide the yield of the structure. We observe a quantum yield of comparable value to experiment assuming typical experimental conditions for a $4$ nm PbS quantum dot.