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Plasmon–Induced Dimerization of Thiazolidine-2, 4-Dione on Silver Nanoparticles - Revealed by Surface-Enhanced Raman Scattering Study
摘要： Surface-enhanced Raman scattering (SERS) study carried on thiazolidine-2, 4-dione (TZD), pharmacologically active heterocyclic compound, points to the presence of TZD dimer formed by plasmon-induced dimerization reaction of TZD on the surface of silver nanoparticles (Ag NP) at TZD concentrations of 10-3 M and above. The evidence for the presence of dimer was obtained from the appearance of a prominent band at 1566 cm-1 corresponding to ν C=C band (a characteristic vibrational band observed for the Knoevenagel condensation reaction products) which is absent in the normal Raman scattering (NRS) spectra of TZD solid/solution. The observed spectrum compares well with the calculated spectrum of dimer obtained using density functional theory (DFT) calculations. The dimerization reaction is plausibly induced by the transfer of hot electrons generated by the non-radiative plasmon decay of Ag NP and the proposed reaction mechanism is discussed. However, at lower concentrations (10-4 to 10-6M), the characteristic dimer peak (1566 cm-1) is absent and the SERS spectra resemble more with the NRS spectrum of TZD with few changes. The spectral analysis supported by DFT calculations showed that TZD molecules undergo deprotonation and get adsorbed on Ag NP surface as enolate forms. The proximity of TZD molecules on the surface of Ag NP is a necessary factor for the dimerization to occur. At lower concentrations, most molecules lie apart and reactions between molecules become less feasible and they remain as monomers on the surface, while at higher concentrations the molecules are closer to each other on Ag NP surface favouring the dimerization reaction to take place leading to the formation of the dimer.
关键词： density functional theory,thiazolidine-2, 4-dione,silver nanoparticles,plasmon-induced dimerization,Surface-enhanced Raman scattering
更新于2025-09-19 17:13:59
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Theoretical, spectroscopical, and experimental investigations of small azomethine molecules for organic solar cells
摘要： Small azomethine molecules (4,4′-bis((2-hydroxy-4-octyloxyphenyl)methylimino)diphenylmethane (BP-DPM) and 4,4′-bis((2-hydroxy-4-octyloxyphenyl)methylimino)diphenyl ether (BP-DPE)) for photovoltaic applications were synthesized by condensation of appropriate arylaldehydes and arylendiamines and characterized using Fourier-transform infrared spectroscopy, 1H NMR, 13C NMR, and liquid chromatography–mass spectrometry. Azomethine molecules are additives in organic solar cells. The effect of a possible energy transfer between BP-DPE and P3HT on the photovoltaic performance of devices employing ternary blends of BP-DPE:P3HT: phenyl-C61-butyric acid methyl ester (PCBM) was investigated by absorption and emission spectra. The devices employing BP-DPE:P3HT:PCBM with 1:4 ratio exhibited a Jsc of 4.2 mA cm?2, Voc of 575 mV, and FF of 0.27 which led to a power conversion efficiency (PCE) of 0.65%. In addition, density functional theory calculations (DFT/B3LYP/6-31G(d)) were used to determine the optimized molecular geometry, highest occupied molecular orbital–lowest unoccupied molecular orbital energies, electronic structures, and the molecular electrostatic potential surfaces of the molecules.
关键词： density functional theory calculations,organic solar cell,azomethines,fluorescence
更新于2025-09-19 17:13:59
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Photoexcitation Processes in Oligomethine Cyanine Dyes for Dye-Sensitized Solar Cellsa??Synthesis and Computational Study
摘要： We report density functional theory (DFT) calculations of three newly synthesized oligomethine cyanine-based dyes as potential TiO2-sensitizers in dye-sensitized solar cells. The three dyes have π-symmetry and the same acceptor side, terminating in the carboxylic anchor, but they differ through the π-bridge and the donor groups. We perform DFT and time-dependent DFT studies and present the electronic structure and optical properties of the dyes alone as well as adsorbed to the TiO2 nanocluster, to provide some predictions on the photovoltaic performance of the system. We analyze theoretically the factors that can influence the short circuit current and the open circuit voltage of the dye-sensitized solar cells. We examine the matching of the absorption spectra of the dye and dye-nanocluster system with the solar irradiation spectrum. We display the energy level diagrams and discuss the alignment between the excited state of the dyes and the conduction band edge of the oxide as well as between the redox level of the electrolyte and the ground state of the dyes. We determine the electron density of the key molecular orbitals and analyze comparatively the electron transfer from the dye to the semiconducting substrate. To put our findings in the right perspective we compare the results of our calculations with those obtained for a coumarin-based dye used in fabricating and testing actual devices, for which experimental data regarding the photovoltaic performance are available.
关键词： optical spectra,titanium dioxide cluster,dye-sensitized solar cells,oligomethine cyanine-based dyes,density functional theory
更新于2025-09-19 17:13:59
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Enhanced Moisture Stability of Cesium Lead Iodide Perovskite Solar Cells- A First-Principles Molecular Dynamics Study
摘要： An understanding of the interaction of water with perovskite is crucial in improving the structural stability of the perovskite. Hence, in this study, the structural and electronic properties of γ-CsPbI3 (220) perovskite surface upon the adsorption of water molecules have been investigated based on density functional theory calculations. Also, we perform the first-principles ab initio molecular dynamics simulations (AIMD) to explore the structural stability of the γ-CsPbI3 (220) perovskite surface in the presence of water molecules, and the results are compared with the conventional cubic CH3NH3PbI3 (100) perovskite surface. The water molecules show stronger interactions with the (220) surface of γ-CsPbI3 than the (100) of CH3NH3PbI3. However, AIMD results demonstrate that the former is much more stable, and no trace of surface degradation has observed upon the adsorption of water molecules.
关键词： water adsorption,density functional theory,perovskite,ab initio molecular dynamics,structural stability
更新于2025-09-19 17:13:59
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Molecular Recognition and Band Alignment in 3D Covalent Organic Frameworks for Cocrystalline Organic Photovoltaics
摘要： Covalent organic frameworks (COFs) have emerged as versatile, functional materials comprised of low-cost molecular building blocks. The permanent porosity, long-range order, and high surface area of 3D-COFs permit co-crystallization with other materials driven by supramolecular interactions. We designed a new subphthalocyanine-based 3-D covalent organic framework (NEUCOF1) capable of forming co-crystals with fullerene (C60) via periodic ball-and-socket binding motifs. The high co-crystalline surface area and long-range order of NEUCOF1 eliminates the typical surface area vs. structural order trade-off in organic photovoltaics (OPVs). We used plane-wave density functional theory (PBE) to minimize NEUCOF1 and NEUCOF1–C60 co-crystals and determine their electronic band structures. Molecular dynamics (MD) simulations showed that dispersive interactions promoting co-crystallinity NEUCOF1–C60 are stable up to 350 K. The band structures at 0 and 350 K suggest that there is a driving force of 0.27 eV for exciton charge transfer to the pocket-bound fullerenes. Charge separation could then occur at the COF-C60 D-A interface, followed by the transfer of the free electron to the nanowire of C60 acceptors with a driving force of 0.20 eV.
关键词： fullerene,subphthalocyanine,co-crystallization,density functional theory,molecular dynamics,Covalent organic frameworks,organic photovoltaics
更新于2025-09-19 17:13:59
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A rational design of excellent light-absorbing dyes with different N-substituents at the phenothiazine for high efficiency solar cells
摘要： Dye-sensitized solar cells (DSSCs) have attracted great interest due to their simple fabrication process and low cost. However, most organic dyes with D-π-A configuration usually exhibit narrow absorption band, leading to poor light harvesting ability and great loss on photon conversion efficiency. In this research, a series of excellent light-absorbing dyes (CC202-I – CC202-III) with different N-substituents at phenothiazine entities based on the champion dye CC202 were designed and investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT). According to the analysis of absorption property, the results demonstrated that different N-substituents (12-crown-4-substituted phenyl, 4-hexoxyphenyl, and bare phenyl) at phenothiazine entities lead to stronger and broader absorption band as well as red-shifted spectra; moreover, larger electronic injection driving force (ΔGinject), regeneration driving force (ΔGreg), capability of light harvested (LHE(λ)strong) and maximal photon generated current (Jph) in CC202-I – CC202-III are observed compared to that of CC202, which further increase JSC. Additionally, a larger VOC can be obtained in CC202-I – CC202-III due to larger dipole moment (μnormal) and slow electron recombination rate. Considering the all calculated characteristics related to JSC, dyes with 12-crown-4-substituted phenyl, 4-hexoxyphenyl, and bare phenyl substituent on phenothiazine can effectively enhance the photoelectric conversion efficiency of DSSCs.
关键词： Dye-sensitized solar cells,Electronic structure,Density functional theory,Light-absorbing
更新于2025-09-19 17:13:59
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Fundamental Limit of the Emission Linewidths of Quantum Dots: An Ab Initio Study of CdSe Nanocrystals
摘要： The emission linewidth of a semiconducting nanocrystal (NC) significantly affects the performance in light-emitting applications but its fundamental limit is still elusive. Herein we analyze exciton-phonon coupling (EPC) from Huang-Rhys (HR) factors using ab initio calculations, and compute emission line shapes of CdSe NCs. When surface traps are absent, acoustic modes are found to dominate EPC. The computed linewidths are mainly determined by the size of NCs, being largely insensitive to the shape and crystal structure. Linewidths obtained in this work are much smaller than most measurements on the homogeneous linewidth, but they are consistent with a CdSe/CdxZn1?xSe (core/shell) NC [Park et al. Nat. Mater. 2019, 18, 249-255]. Based on this comparison, it is concluded that the large linewidths in most experiments originated from internal fields by surface (or interface) traps or quasi-type Ⅱ band alignment that amplify EPC. Thus, the present results on NCs with ideal passivation provide the fundamental minimum of homogeneous linewidths, indicating that only the CdSe/CdxZn1?xSe NC has achieved this limit through well-controlled synthesis of the shell structure. To further verify the role of internal fields, we model NCs with charged surface defects. We find that the internal field significantly increases HR factors and linewidths, in reasonable agreements with experiments on single cores. By revealing the fundamental limit of emission linewidths of quantum dots, this work will pave the way to engineering quantum dots with ultrasharp spectrum.
关键词： nanocrystals,photoluminescence,homogeneous linewidth,exciton-phonon coupling,surface traps,density functional theory,electroluminescence,quantum dots
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Machine learning defect properties in Cd-based chalcogenides
摘要： Impurity energy levels in the band gap can have serious consequences for a semiconductor’s performance as a photovoltaic absorber. Data-driven approaches can help accelerate the prediction of point defect properties in common semiconductors, and thus lead to the identification of potential deep lying impurity states. In this work, we use density functional theory (DFT) to compute defect formation energies and charge transition levels of hundreds of impurities in CdX chalcogenide compounds, where X = Te, Se or S. We apply machine learning techniques on the DFT data and develop on-demand predictive models for the formation energy and relevant transition levels of any impurity atom in any site. The trained ML models are general and accurate enough to predict the properties of any possible point defects in any Cd-based chalcogenide, as we prove by testing on a few selected defects in mixed chalcogen compounds CdTe0.5Se0.5 and CdSe0.5S0.5. The ML framework used in this work can be extended to any class of semiconductors.
关键词： machine learning,point defects,CdTe,density functional theory,chalcogenides
更新于2025-09-19 17:13:59
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[IEEE 2019 1st International Conference on Advances in Science, Engineering and Robotics Technology (ICASERT) - Dhaka, Bangladesh (2019.5.3-2019.5.5)] 2019 1st International Conference on Advances in Science, Engineering and Robotics Technology (ICASERT) - Effect of Solar Concentration on Performance of Perovskite Solar Cell: A detailed balance study
摘要： As a perovskite material, methylammonium lead iodide has become more popular for its flexibility, low-cost, lightweight, thin film and high power conversion capability in photovoltaic research community. In this work, we have explored the effect of solar concentration on PV performance for methylammonium lead iodide (CH3NH3PbI3) perovskite solar cell computationally. To calculate the band structure, bandgap and density of states (DOS) of CH3NH3PbI3, density functional theory (DFT) is used here. The detailed balance method is employed to figure out the effect of concentration on performance of perovskite solar cell. We have calculated performance parameters of CH3NH3PbI3 solar cell for two solar spectra AM 1.5 G and AM 1.5 D. All calculations have been performed at different solar concentrations ranging from no concentration to full concentration for both types solar spectra. It is found that the solar cell efficiency at 1.5 G spectrum is higher than 1.5 D solar spectrum at any solar concentration. These results may impact future research on perovskite solar cell.
关键词： Perovskite solar cell (PSC),solar concentration,PCE,density functional theory (DFT),detailed balance limit
更新于2025-09-16 10:30:52
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Non enzymatic fluorometric determination of glucose by using quenchable g-C3N4 quantum dots
摘要： A non-enzymatic fluorometric assay is described for the determination of glucose. The method is based on the use of g-C3N4 quantum dots (QDs) that have good water solubility. The QDs were synthesized by a one-step solvothermal process using formamide as precursor. The QDs possess an average size of ~5 nm, a band gap of 3.0~3.5 eV, and strong blue fluorescence (with excitation/emission maxima at 400/447 nm). Fluorescence is quenched by glucose (which acts as the electron acceptor) via an electron transfer mechanism. Comprehensive spectroscopy and density functional theory calculations show that the selectivity of the fluorescent probe can be attributed to the presence of N-H bonds that are formed between the QDs (mainly at plane edges) and glucose. The interaction forces lead to the formation of localized states for capturing hot electrons. This results in a decrease in the band gap and a reduction in fluorescence intensity. The probe is selective over some typical interfering species (such as cysteine and albumin) which often are present in the urine of diabetics. The method has a linear response in the 0.2 to 5.0 mM glucose concentration range and a 0.2 mM detection limit.
关键词： Density functional theory calculations,Fluorescent probe,Fluorescence quenching,Inorganic nanomaterials
更新于2025-09-16 10:30:52