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Phonon-Driven Energy Relaxation in PbS/CdS and PbSe/CdSe Core/Shell Quantum Dots
摘要： We study the impact of the chemical composition on phonon-mediated exciton relaxation in the core/shell quantum dots (QDs), with 1-nm core made of PbX and the monolayer shell made of CdX, where X=S and Se. For this, time-domain non-adiabatic dynamics (NAMD) based on Density Functional Theory (DFT) and Surface Hopping techniques are applied. Simulations reveal twice faster energy relaxation in PbS/CdS than PbSe/CdSe due to dominant couplings to higher-energy optical phonons in structures with sulfur anions. For both QDs, the long-living intermediate states associated with the core-shell interface govern the dynamics. Therefore, a simple exponential model is not appropriate, and the four-state irreversible kinetic model is suggested instead, predicting 0.9 ps and 0.5 ps relaxation rates in PbSe/CdSe and PbS/CdS QDs, respectively. Thus, 2-nm PdSe/CdSe QDs with a single monolayer shell exhibit the phonon-mediated relaxation time sufficient for carrier multiplications to outpace energy dissipation and benefit the solar conversion efficiency.
关键词： Density Functional Theory,phonon-driven energy relaxation,PbSe/CdSe,PbS/CdS,core/shell quantum dots,Surface Hopping techniques,non-adiabatic dynamics
更新于2025-09-23 15:21:01
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Computational high throughput screening of inorganic cation based halide perovskites for perovskite only tandem solar cells
摘要： We search for homovalent alternatives for A, B, and X-ions in ABX3 type inorganic halide perovskites suitable for tandem solar cell applications. We replace the conventional A-site organic cation CH3NH3, by 3 inorganic cations, Cs, K, and Rb, and the B site consists of metals; Cd, Hg, Ge, Pb, and Sn This work is built on our previous high throughput screening of hybrid perovskite materials (Kar et al 2018 J. Chem. Phys. 149, 214701). By performing a systematic screening study using Density Functional Theory (DFT) methods, we found 11 suitable candidates; 2 Cs-based, 3 K-based and 6 Rb-based that are suitable for tandem solar cell applications.
关键词： tandem solar cells,inorganic perovskites,density functional theory
更新于2025-09-23 15:21:01
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Osmium sensitizer with enhanced spin-orbit coupling for panchromatic dye-sensitized solar cells
摘要： Low-lying triplet metal-to-ligand charge transfer (3MLCT) transitions of osmium complexes induced by spin-orbit coupling (SOC) is promising to extend photocurrent response when applied to dye-sensitized solar cells. In this study, we present a newly designed osmium complex (coded CYC-33O), incorporating a 2-thiohexyl-3,4-ethylenedioxythiophene functionalized bipyridyl ancillary ligand to red-shift the absorption and enhance the absorbance of both singlet and triplet MLCT transitions. Time-dependent density functional theory (TDDFT) calculations clearly signify the reinforced 1MLCT and 3MLCT transitions of CYC-33O mainly originate from osmium to 4,4',4"-tricarboxy-2,2':6',2"-terpyridine anchoring ligand, advantaging the heterogeneous electron transfer between CYC-33O and TiO2. The device sensitized with CYC-33O exhibits the panchromatic conversion beyond 1000 nm, yielding the photocurrent density of 19.38 mA cm–2 which is much higher than those of the cells based on the ruthenium analogue (CYC-33R) and model osmium complex (Os-3) sensitizers.
关键词： dye-sensitized solar cell,triplet metal-to-ligand charge transfer (3MLCT),ruthenium complex,spin-orbit coupling (SOC),osmium complex,time-dependent density functional theory (TDDFT)
更新于2025-09-23 15:21:01
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AIP Conference Proceedings [AIP Publishing 3RD INTERNATIONAL CONFERENCE ON CONDENSED MATTER AND APPLIED PHYSICS (ICC-2019) - Bikaner, India (14a??15 October 2019)] 3RD INTERNATIONAL CONFERENCE ON CONDENSED MATTER AND APPLIED PHYSICS (ICC-2019) - Computational study on 8-quinolinolato-alkali, an electron transporting material for OLED devices
摘要： Organic light-emitting diodes (OLEDs) materials have occupied significance in device applications due to their lightweight, thin, quick switching speed, flexible, easy to fabricate and low-cost features. The 8-quinolinolato-lithium (Liq) is commonly used as an electron injector in the layer of OLEDs. Herein, we study 8-quinolinolato-sodium (Naq) and 8-quinolinolato-potassium (Kq) and compare them with Liq using density functional theory approach. We analyze the molecular structure of 8-quinolinolate-alkali (Mq) for M = Li, Na and K and notice that the structure of Mq remains planar for all the three substitutions. The increased dipole moments of Mq with the change of substitution (M) suggest that its enhanced solubility in polar solvents, which tends to reduce the electron injection barrier. Furthermore, the higher polarizability of Naq and Kq indicates that the molecule is chemically more reactive than Liq and therefore, is expected to respond quickly when the field is applied. Moreover, the electron affinities of Mq increase with the substitution of Na and K, which is also desirable for improved electron transport behavior. However, the reorganization energy of Naq and Kq is slightly higher than that of Liq, which is not desirable for the transport of charge carriers in OLED devices. Therefore, the findings of this study demand further assessment for the application of Naq and Kq instead of Liq in OLED devices.
关键词： electron transporting material,8-quinolinolato-alkali,density functional theory,OLED
更新于2025-09-23 15:21:01
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Density Functional Theory Study on the Donating Strength of Donor Systems in Dye-Sensitized Solar Cells
摘要： The electron-donating strength of donor (D) moieties in thirteen donor-π-acceptor systems (D1-π-A to D13-π-A wherein -π- and A represent butadiene and cyanoacrylic acid units, respectively) have been studied using B3LYP/cc-pVDZ level density functional theory (DFT) calculations. The selected D moieties are encountered as a part of an organic sensitizer molecule in dye-sensitized solar cell (DSSC) applications. When D moiety is joined with π-A, a certain amount of electron donation from D to A occurs leading to increase in electron density at the A site of D-π-A compared to A site of π-A. This electron reorganization is quantified in terms of the change in molecular electrostatic potential (MESP) minimum (ΔVmA) at the acceptor site, the CN group of the cyanoacrylic acid. The ΔVmA is always negative, in the range -11.0 to -2.6 kcal/mol which provides a quick assessment of the rank order of the electron-donating nature of the D moieties in the ground state of D-π-A. The optical, and photovoltaic properties of D and D-π-A systems are also determined at TD-CAM-B3LYP/cc-pVDZ//B3LYP/cc-pVDZ level. An absorption red shift (Δλmax) in the range 81 – 242 nm is observed when D moieties change to D-π-A systems. The ground state property ΔVmA showed a strong linear correlation with the excited state property Δλmax. Further, ΔVmA is found to be proportional to the open-circuit voltage (Voc). The resemblance of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of the D-π–A system with the respective energies of donor and π-A systems shows that donor tunes HOMO, while π-A tunes LUMO. Among the thirteen D-π-A systems, N,N-dialkylaniline, and julolidine are rated as the best donors for the photovoltaic applications. This study shows that MESP based assessment of donating strength of donor systems offers a powerful rational design strategy for the development of efficient dyes for DSSC applications.
关键词： donor-π-acceptor systems,electron-donating strength,molecular electrostatic potential,dye-sensitized solar cells,density functional theory
更新于2025-09-23 15:21:01
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Tailoring Bond Topologies in Open-Shell Graphene Nanostructures
摘要： Polycyclic aromatic hydrocarbons exhibit a rich spectrum of physico-chemical properties depending on the size, and more critically, on the edge and bond topologies. Among them, open-shell systems – molecules hosting unpaired electron densities – represent an important class of materials for organic electronic, spintronic and optoelectronic devices, but remain challenging to synthesize in solution. We report the on-surface synthesis and scanning tunneling microscopy- and spectroscopy-based study of two ultra-low-gap open-shell molecules, namely peri-tetracene, a benzenoid graphene fragment with zigzag edge topology, and dibenzo[a,m]dicyclohepta[bcde,nopq]rubicene, a non-benzenoid non-alternant structural isomer of peri-tetracene with two embedded azulene units. Our results provide an understanding of the ramifications of altered bond topologies at the single-molecule scale, with the prospect of designing functionalities in carbon-based nanostructures via engineering of bond topology.
关键词： open-shell polycyclic aromatic hydrocarbons,atom manipulation,non-alternant polycyclic aromatic hydrocarbons,scanning tunneling microscopy,density functional theory,scanning tunneling spectroscopy
更新于2025-09-23 15:21:01
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Galliuma??Borona??Phosphide ($$\hbox {GaBP}_{2}$$): a new IIIa??V semiconductor for photovoltaics
摘要： Using machine learning (ML) approach, we unearthed a new III–V semiconducting material having an optimal bandgap for high-efficient photovoltaics with the chemical composition of Gallium–Boron–Phosphide (GaBP2, space group: Pna21). ML predictions are further validated by state-of-the-art ab initio density functional theory simulations. The stoichiometric Heyd–Scuseria–Ernzerhof bandgap of GaBP2 is noted to be 1.65 eV, a close ideal value (1.4–1.5 eV) to reach the theoretical Queisser–Shockley limit. The calculated electron mobility is similar to that of silicon. Unlike perovskites, the newly discovered material is thermally, dynamically and mechanically stable. Above all the chemical composition of GaBP2 is non-toxic and relatively earth abundant, making it a new generation of PV material. Using ML, we showed that with a minimal set of features, the bandgap of III–III–V and II–IV–V semiconductor can be predicted up to an RMSE of less than 0.4 eV. We have presented a set of scaling laws, which can be used to estimate the bandgap of new III–III–V and II–IV–V semiconductor, with three different crystal phases, within an RMSE of 0.4 eV.
关键词： Gallium–Boron–Phosphide,photovoltaics,GaBP2,III–V semiconductor,density functional theory,machine learning
更新于2025-09-23 15:21:01
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An extended chiral surface coordination network based on Ag <sub/>7</sub> -clusters
摘要： We present an extended metal-coordinated structure obtained by deposition of trimesic acid (TMA) onto the Ag(111) surface under ultra-high vacuum conditions followed by annealing to 510 K. Scanning tunneling microscopy and density functional theory calculations reveal the structure to consist of metal clusters containing seven Ag atoms each, coordinated by six dehydrogenated TMA molecules. The molecules are asymmetrically arranged, resulting in a chiral structure. The calculations confirm that this structure has a lower free energy under the experimental conditions than the hydrogen-bonded structures observed after annealing at lower temperatures. We show that the formation of such large metal clusters is possible due to the low adatom formation energy on silver and the relatively strong Ag-O bond in combination with a good lattice match between the structure and the Ag surface.
关键词： Ag7-clusters,TMA molecules,metal-coordinated structure,density functional theory,chiral structure
更新于2025-09-23 15:21:01
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<i>Ab Initio</i> Spin-Strain Coupling Parameters of Divacancy Qubits in Silicon Carbide
摘要： Cubic silicon carbide is an excellent platform for integration of defect qubits into established wafer-scale device architectures for quantum information and sensing applications, where a divacancy qubit, which is similar to the negatively charged nitrogen-vacancy (NV) center in diamond, has favorable coherence properties. We demonstrate by means of density-functional-theory calculations that for most types of distortion the 3C divacancy exhibits slightly smaller spin-strain coupling parameters but greater spin-stress coupling parameters in comparison with the diamond NV. We predict that high-quality 3C-SiC thin films hosting divacancy qubits are prospective platforms for quantum-enhanced pressure-sensor devices.
关键词： spin-strain coupling,quantum sensing,density-functional theory,divacancy qubits,silicon carbide
更新于2025-09-23 15:21:01
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Imaging empty states on the Ge(100) surface at 12 K
摘要： Our understanding of bias-dependent scanning-tunneling-microscopy (STM) images is complicated not only by the multiplicity of the surface electronic structure, but also the manifold tunneling effects in probing semiconductor surfaces having directional dangling- and covalent-bond orbitals. Here we present a re?ned interpretation of empty-state STM images from the model semiconductor surface, Ge(100), on the basis of measurements at low temperature (12 K) combined with density-functional-theory calculations. In the lower-bias regime ((cid:2)1.6 V), the electron tunneling is found to occur predominantly in antibonding dangling-bond or/and dimer-bond states (π ? 2 , and σ ?) of Ge(100) at the surface-parallel wave vector k(cid:3) = 0, leading to the tunneling current maxima located directly on the dimer rows. At higher biases (e.g., at 2 V), the current maxima are shifted to the position in the troughs between the dimer rows, because the tunneling occurs ef?ciently in the π ? 2 states at k(cid:3) (cid:4)= 0 associated with the dimer-up atoms of two adjacent dimer rows, i.e., because of increased sideways tunneling. Thus, the empty-state STM images of Ge(100), albeit strongly bias-dependent, re?ect the dimer arrangement rather than the backbonds and surface resonances at all experimental conditions used. The results are also discussed in comparison with the counterpart system of Si(100).
关键词： STM,density-functional-theory,Ge(100),tunneling,semiconductor surfaces
更新于2025-09-23 15:21:01