Twisting enabled charge transfer excitons in epitaxially fused quantum dot molecules

TL;DR

This study demonstrates that twisting epitaxially fused quantum dot molecules can effectively modulate charge-transfer excitons, challenging traditional material selection rules and enabling better control over exciton properties for energy devices.

Contribution

It reveals that twisting can control exciton localization and energy levels in QD molecules, providing a new approach to manipulate exciton nature beyond conventional band alignment rules.

Findings

Twisting modulates orbital localization and charge separation.

Unexpected reverse ordering of exciton states due to many-body effects.

Successful generation of charge-transfer excitons in both homodimer and heterodimer QD molecules.

Abstract

Charge-transfer excitons possessing long radiative lifetime and net permanent dipole moment are highly appealing for quantum dot (QD) based energy harvesting and photodetecting devices, in which the efficiency of charge separation after photo-excitation limits the device performance. Herein, using a hybrid time-dependent density functional theory, we have demonstrated that the prevailing rule of selecting materials with staggered type-II band alignment for realization of charge-transfer exciton breaks down in epitaxially fused QD molecules. The excitonic many-body effects are found to be significant and distinct depending on the exciton nature, causing unexpected reverse ordering of exciton states. Strikingly, twisting QD molecule appears as an effective means of modulating the orbital spatial localization towards charge separation that is mandatory for a charge-transfer exciton. Meanwhile, it manifests the intra-energy-level splitting that counterbalances the distinct many-body effects felt by excitons of different nature, thus ensuring the successful generation of energetically favourable charge-transfer exciton in both homodimer and heterodimer QD molecules. Our study extends the realm of twistroincs into zero-dimensional materials, and provides a genuine route of manipulating the exciton nature in QD molecules.