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Register a new userTwisting enabled charge transfer excitons in epitaxially fused quantum dot molecules
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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.
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Many-body effect and strong Coulomb interaction in monolayer transition metal dichalcogenides lead to shrink the intrinsic bandgap, originating from the renormalization of electrical/optical bandgap, exciton binding energy, and spin-orbit splitting. This renormalization phenomenon has been commonly observed at low temperature and requires high photon excitation density. Here, we present the augmented bandgap renormalization in monolayer MoS_2 anchored on CsPbBr_3 perovskite quantum dots at room temperature via charge transfer. The amount of electrons significantly transferred from perovskite gives rise to the large plasma screening in MoS_2. The bandgap in heterostructure is red-shifted by 84 meV with minimal pump fluence, the highest bandgap renormalization in monolayer MoS_2 at room temperature, which saturates with further increase of pump fluence. We further find that the magnitude of bandgap renormalization inversely relates to Thomas-Fermi screening length. This provides plenty of room to explore the bandgap renormalization within existing vast libraries of large bandgap van der Waals heterostructure towards practical devices such as solar cells, photodetectors and light-emitting-diodes.
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