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Charged excited states can accumulate on the surface of colloidal quantum dots (QDs), affecting their optoelectronic properties. In experimental samples, QDs often have non-stoichiometric structures, giving rise to cation-rich and anion-rich nanostructures. We explore the effect of charge on the ground- and excited-state properties of CdSe non-stoichiometric QDs (NS-QDs) of ∼1.5 nm in size using density functional theory calculations. We compare two cases: (i) NS- QDs with a charge introduced by direct hole or electron injection and (ii) neutral NS-QDs with one removed surface ligand (with a dangling bond). Our calculations reveal that a neutral dangling bond has an effect on the electronic structure similar to that of the electron injection for the Cd-rich NS-QDs or hole injection for the Se-rich NS-QDs. In Cd-rich structures, either the injection of an electron or the removal of a passivating ligand results in the surface-localized half-filled trap state inside the energy gap. For Se-rich structures, either the injection of a hole or the removal of a ligand introduces surface-localized unoccupied trap states inside the energy gap. As a result, the charge localization formed by these two approaches leads to an appearance of low-energy electronic transitions strongly red-shifted from the main excitonic band of NS-QDs. These transitions related to a negative charge or a dangling bond exhibit weak optical activity in Cd-rich NS-QDs. Transitions related to a positive charge or a dangling bond are optically forbidden in Se-rich NS-QDs. In contrast, electron injection in Se-rich NS-QDs strongly increases the optical activity of the lowest- red-shifted charge-originated states. 

Two-dimensional organic–inorganic hybrid lead halide perovskites are of interest for photovoltaic and light emitting devices due to their favorable properties that can be tuned. Here we use density functional theory to model two-dimensional lead halide perovskites of different thicknesses and using two different hallogens. Excited-state optoelectronic properties of the perovskite models are examined using excited-state dynamics treated by reduced density matrix method. Nonadiabatic couplings were computed based on the on-the-fly approach along a molecular dynamics trajectory at ambient temperatures. The density matrix-based equation of motion for electronic degrees of freedom was used to determine the dynamics of electronic degrees of freedom. We observe that the thickness of the perovskite layer shows a redshift in the absorption spectra with increasing thickness but has minimal effect on the photoluminescence quantum yield of the material. 

Heterostructure quantum dots (QDs) are composed of two QD nanocrystals (NCs) conjoined at an interface. They are useful in applications such as photovoltaic solar cells. The properties of the interface between the NCs determine the efficiency of electron–hole recombination rates and charge transfer. Therefore, a fundamental understanding of how this interface works between the two materials is useful. To contribute to this understanding, we simulated two isolated heterostructure QD models with Janus-like geometry composed of Cd33Se33 + Pb68Se68 NCs. The first Janus-like model has a bond connection between the two NCs and is approximately 16 × 17 × 29 Å3 in size. The second model has a through-space connection between the NCs and is approximately 16 × 17 × 31 Å3. We use density functional theory to simulate the ground state properties of these models. Nonadiabatic on-the-fly couplings calculations were then used to construct the Redfield Tensor, which described the excited state dynamics due to nonradiative relaxation. From our results, we identified a qualitative trend which shows that having a bond connecting the two NCs reduces hole relaxation time. We also identified for a sample of electron–hole excitations pairs that the through-bond model allows for a net positive or negative numerical net charge transfer, depending on the excitation pair. 

Lead halide perovskites (LHP) are of interest for light-emitting applications due to the tunability of their bandgap across the visible and near-infrared spectrum (IR) coupled with efficient photoluminescence quantum yields (PLQY). It is widely speculated that photoexcited electrons and holes spatially separate into large negative (electron) and positive (hole) polarons. Polarons are expected to be optically active. With the observed optoelectronic signatures expecting to show potential excited states within the polaronic potential well. From the polaron excited-state we predict that large polarons should be capable of spontaneous emission, photoluminescence, in the mid-IR to far-IR regime based on the concept of inverse occupations within the polaron potential well. Here we use density functional theory (DFT), including spin–orbit coupling interactions, for calculations on a two-dimensional Dion-Jacobson (DJ) lead chloride perovskite atomistic model of various sizes as a host material for either negative or positive polarons to examine the effects of size on polaron formation. This work provides computational evidence that polaron formation through selective charge injection does not show the same level of localisation for positive and negative polarons. 

Metal clusters with 10 to 100 atoms supported by a solid surface show electronic structure typical of molecules and require ab initio treatments starting from their atomic structure, and they also can display collective electronic phenomena similar to plasmons in metal solids. We have employed ab initio electronic structure results from two different density functionals (PBE and the hybrid HSE06) and a reduced density matrix treatment of the dissipative photodynamics to calculate light absorbance by the large Ag clusters Ag N , N = 33, 37(open shell) and N = 32, 34 (closed shell), adsorbed at the Si(111) surface of a slab, and forming nanostructured surfaces. Results on light absorption are quite different for the two functionals, and are presented here for light absorbances using orbitals and energies from the hybrid functional giving correct energy band gaps. Absorption of Ag clusters on Si increases light absorbance versus photon energy by large percentages, with peak increases found in regions of photon energies corresponding to localized plasmons. The present metal clusters are large enough to allow for modelling with continuum dielectric treatments of their medium. A mesoscopic Drude–Lorentz model is presented in a version suitable for the present structures, and provides an interpretation of our results. The calculated range of plasmon energies overlaps with the range of solar photon energies, making the present structures and properties relevant to applications to solar photoabsorption and photocatalysis. 

Spatial confinement of charge carriers in nanosize semiconductor quantum dots (QDs) results in highly tunable, size-dependent optoelectronic properties that can be utilized in various commercial applications. Although in such nanostructures, non-stoichiometry is frequently encountered using conventional synthesis techniques, it is not often addressed or considered. Here, we perform ab initio molecular dynamics simulations on non-stoichiometric CdSe clusters to study the phonon-mediated charge carrier relaxation dynamics. We model cation-rich and anion-rich QDs passivated with monocharged neutralizing ligands of different sizes. Our studies confirm the presence of localized trap states at the valence band edge in only anion-rich QDs due to the presence of undercoordinated exposed surface Se atoms. Noteworthily, these localized states disappear when using bulkier ligands. Calculations reveal that the size of the ligands controls the crystal vibrations and electron–phonon coupling, while ligand coordination number affects the electronic structure. For a particular non-stoichiometric CdSe QD, a change of a ligand can either increase or decrease the total electron relaxation time compared to that of stoichiometric QDs. Our results emphasize the importance of ligand engineering in non-stoichiometric QDs for photoinduced dynamics and guide future work for the implementation of improved materials for optoelectronic devices.