We also find slightly larger shifts for the 001 orientation attachment resulting from shorter core-to-core distances. The dependence on the shell thickness is mainly governed by changes in the core-to-core distance mitigated by changes in the confinement energy of the quasi-electron as the shell thickness is varied. As the neck grows beyond ≈ 2 nm, Δ g increases and slowly approach a plateau while δ E g continually increases across all neck sizes studied. We find that below an onset width of about ≈ 2 nm, namely, for neck widths that are smaller than the size of the CdSe core, the changes in δE g and Δ g are rather small. 2, we plot the overall change in the fundamental gap ( δE g = δE e − δE h ≈ δE e, where δE e/h are the changes in the quasi-electron/hole energies in the CQDMs relative to the monomer CQD) as a function of the neck width for all dimers studied in this work. Therefore, the main contribution to the changes in the fundamental gap due to hybridization can be assigned to the quasi-electron (Δ g ≈ Δ e), which is shown in the lower right panel of Fig. However, since the quasi-hole has a relatively heavy effective mass and experiences a large band offset at the core/shell interface, it remains localized to the CdSe core regions (and not the CdS shell), resulting in negligibly small hybridization energies (Δ h ≪ 1 meV). Together, both effects are expected to change the overall fundamental gap by Δ g = Δ h + Δ e. Similarly, the quasi-hole tunneling splitting is given by Δ h = 1 2 E h 1 − E h 2. The hybridization energy of the electron (Δ e, sometime referred to as the “tunneling splitting”) can then be approximated by half the energy difference between the two lowest quasi-electron states, Δ e = 1 2 E e 2 − E e 1. The quasi-electron ground and first excited orbitals can roughly be described by a symmetric and asymmetric superposition of the 1 S e-like envelope functions of the QD monomer building blocks. Typical solutions for the quasi-electron wavefunctions for the ground and first excited states are shown in Fig. Moreover, comparing the postdictions of our model to the experimental measurements, we find excellent agreement in describing the overall spectral red shifts in photoluminescence (PL) and in the absorption as well as spectral broadening and changes in oscillator strengths. A related effect of the quasi-hole was reported for InAs/GaAs dimers grown by molecular beam epitaxy, 20–23 where the symmetry of the hole was correlated with the distance between the two InAs/GaAs quantum dots. Interestingly, we also find that the quasi-hole comprising the lowest exciton changes symmetry with the orientation of attachment. The work sets an atomistic theoretical framework to also predict further optoelectronic characteristics of colloidal quantum dots. Strong excitonic redshifts are predicted for dimers composed of fully fused quantum dots (QDs) with a thin shell. The modifications of the electronic properties in the CQDMs are attributed to a combination of factors, including hybridization energies, loss of confinement in the presence of a neck (which we hereon refer to as “deconfinement”), and modified electron–hole interactions. 19 The calculations and theoretical analysis allow us to delineate the roles of confinement, hybridization, and strain in different planes of attachment while varying the shell thickness and neck girth. The configurations of all the CQDMs were optimized using mechanical force-fields, 16,17 and the corresponding electronic and optical properties were described within the semiempirical pseudo-potential model 18 combined with a nonperturbative description of electron–hole correlations. In this work, we performed atomistic calculations to determine the structure and electronic properties of CQDM composed of two fused CdSe/CdS core–shell CQDs as a model system.
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