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Photovoltaic cells with various azo dyes as components of the active layer
摘要： The photovoltaic response of six cells with an active layer of heterocyclic azo dyes is presented for the first time. The active azo layers differed in the type of substituent (i.e. electron-donating: CH3, OCH3 and electron withdrawing: Br). We showed that by changing the substituent in the heterocyclic azo dye we change the power efficiency of the device. It should be mentioned that all presented data showed high potential of heterocyclic azo dyes for effective photovoltaic output. The studied heterocyclic azo dyes have higher photovoltaic parameters than those obtained for photovoltaic cell with 4-Diethoxyphenylsilylazobenzene.
关键词： Theoretical DFT calculations,Photovoltaic cell,Thin films,Heterocyclic azo dyes,Current density-voltage characteristics
更新于2025-09-23 15:19:57
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Symmetry controlled photo-selection and charge separation in butadiyne-bridged donora??bridgea??acceptor compounds
摘要： Electron transfer (ET) in donor-bridge-acceptor (DBA) compounds depends strongly on the structural and electronic properties of the bridge. Among the bridges that support donor - acceptor conjugation, alkyne bridges have attractive and unique properties: they are compact, possess linear structure permitting access to high symmetry DBA structures, and allow torsional motion of D and A, especially for longer bridges. We report conformation dependent electron transfer dynamics in a set of novel DBA compounds featuring butadiyne (C4) bridge, N-isopropyl-1,8-napthalimide (NAP) acceptors, and donors that span a range of reduction potentials (trimethyl silane (Si-C4-NAP), phenyl (Ph-C4-NAP), and dimethyl aniline (D-C4-NAP)). Transient mid-IR absorption spectra of the C≡C bridge stretching modes, transient spectra in the visible range and TD-DFT calculations were used to decipher the ET mechanisms. We found that the electronic excited state energies and, especially, the transition dipoles (S0→Sn) depend strongly on the dihedral angle (θ) between D and A and the frontier orbital symmetry, offering an opportunity to photo-select particular excited states with specific ranges of dihedral angles by exciting at chosen wavelengths. For example, excitation of D-C4-NAP at 400 nm predominantly prepares an S1 excited state in the planar conformations (θ ~ 0) but selects an S2 state with θ ~ 90o, indicating the dominant role of the molecular symmetry in the photophysics. Moreover, the symmetry of the frontier orbitals of such DBA compounds not only defines the photo-selection outcome, but also determines the rate of the S2→S1 charge separation reaction. Unprecedented variation of the S2-S1 electronic coupling with θ by over four orders of magnitude results in slow ET at θ ca. 0o and 90o but extremely fast ET at θ of 20-60o. The unique features of high-symmetry alkyne bridged DBA structures enable frequency dependent ET rate selection and make this family of compounds promising targets for the vibrational excitation control of ET kinetics.
关键词： transient absorption spectroscopy,electron transfer,donor-bridge-acceptor,TD-DFT calculations,butadiyne bridge
更新于2025-09-23 15:19:57
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Structure and Conformation of a Crystalline P3HT Film Adsorbed on an Alkanethiol Self-Assembled Monolayer Deposited on Gold
摘要： All-atom molecular dynamics simulations are performed to investigate the structural and conformational properties of a regioregular poly(3-hexylthiophene) (P3HT) crystal in the presence of a gold (Au) substrate terminated with an n-alkanethiol self-assembled monolayer (SAM). The employed orientation of the P3HT crystals deposited on the SAM is the edge-on, since this orientation is believed to be the most energetically favorable and stable, also yielding the highest charge carrier mobility in organic thin-film transistors. The unit cell of the overall Au/SAM interfacial layer is obtained through detailed ab initio calculations. Systems with a varying number of P3HT stacks on the Au/SAM substrate are studied with an all-atom force field in order to elucidate the effect of polymer thickness on the structural properties of the system. All final structures are found to be stable and well-equilibrated. Insights into the P3HT crystal structure are provided for the P3HT layers in direct contact with the SAM, but also for those deeper in the polymer film. According to the simulations, the majority of conformational and packing properties of the P3HT film are practically similar to those of the bulk crystalline P3HT material, implying that its structure remains unaffected by the presence of the underlying Au/SAM substrate.
关键词： DFT calculations,semiconducting polymers,molecular dynamics simulations,self-assembled monolayers,P3HT
更新于2025-09-23 15:19:57
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Structure of heroin in a solution revealed by chiroptical spectroscopy
摘要： In this work, the 3-D structure of the well-known opioid drug heroin in a solution was investigated. The goal was to provide a complete and detailed description of the stable conformers with their relative abundances. This knowledge is very important from the pharmaceutical and forensic point of view as it could help significantly with deeper understanding of heroin's metabolism and the development of antagonist medicines for the case of an overdose. As heroin is a chiral compound with five stereogenic centres, the methods of chiroptical spectroscopy supplemented by density functional theory (DFT) calculations were applied to study its conformations in chloroform solution. The selected chiroptical methods, namely, electronic circular dichroism (ECD) and vibrational circular dichroism (VCD), are inherently sensitive to the 3-D structure of small- to medium-sized chiral organic molecules. A thorough conformational analysis revealed four stable conformers of heroin in chloroform solution, where the conductor-like polarizable continuum model of the solvent was used for all the calculations. The simulated ultraviolet (UV), infrared (IR), ECD, and VCD spectra were compared with the experimental ones and very good agreement was found, which enabled a detailed structure description and interpretation of the spectra. Chiroptical spectroscopy in combination with DFT calculations proved to be a very sensitive tool for the analysis of the 3-D structure of heroin in a solution in contrast with conventional spectroscopic methods. Especially, the application of VCD seems to be a promising approach for monitoring structural changes, for instance, those caused by solvents or interactions with other agents.
关键词： 3-D structure,DFT calculations,drugs,chiroptical spectroscopy,circular dichroism,heroin
更新于2025-09-23 15:19:57
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Theoretical Study of a Class of Organic Da????a??A Dyes for Polymer Solar Cells: Influence of Various ??a??Spacers
摘要： A class of D‐π‐A compounds that can be used as dyes for applications in polymer solar cells has theoretically been designed and studied, on the basis of the dyes recently shown by experiment to have the highest power conversion efficiency (PCE), namely the poly[4,8‐bis(5‐(2‐(PBDTS‐TZNT) butylhexylthio)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b’]dithiophene‐2,6‐diyl‐alt‐TZNT] and poly[4,8‐bis(4‐fluoro‐5‐(2‐butylhexylthio)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b’]dithiophene‐2,6‐ diyl‐alt‐TZNT] (PBDTSF‐TZNT) substances. Electronic structure theory computations were carried out with density functional theory and time‐dependent density functional theory methods in conjunction with the 6?311G (d, p) basis set. The PBDTS donor and the TZNT (naphtho[1,2‐c:5,6‐c]bis(2‐octyl‐[1,2,3]triazole) acceptor components were established from the original substances upon replacement of long alkyl groups within the thiophene and azole rings with methyl groups. In particular, the effects of several π‐spacers were investigated. The calculated results confirmed that dithieno[3,2‐b:2′,3′‐d] silole (DTS) acts as an excellent π‐linker, even better than the thiophene bridge in the original substances in terms of well‐known criteria. Indeed, a PBDTS‐DTS‐TZNT combination forms a D‐π‐A substance that has a flatter structure, more rigidity in going from the neutral to the cationic form, and a better conjugation than the original compounds. The highest occupied molecular orbital (HOMO)‐lowest unoccupied molecular orbital (LUMO) energy gap of such a D‐π‐A substance becomes smaller and its absorption spectrum is more intense and red‐shifted, which enhances the intramolecular charge transfer and makes it a promising candidate to attain higher PCEs.
关键词： DFT calculations,PCEs,DTS,PBDTS‐TZNT and PBDTSF‐TZNT,D‐π‐A dyes,polymer solar cells
更新于2025-09-23 15:19:57
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Modulating Charge-Carrier Dynamics in Mn-Doped All-Inorganic Halide Perovskite Quantum Dots through the Doping-Induced Deep Trap States
摘要： Transition metal ions doping has been demonstrated effective to tune the photoluminescence properties of perovskite quantum dots (QD). However, it would inevitably introduce defects in the lattice. As the Mn concentration increases, the Mn dopant PL quantum yield (PLQY) first increases and then decreases. Herein, the influence of the dopant and the defect states on the photophysics in Mn doped CsPbCl3 QDs was studied by time-resolved spectroscopies, while the energy levels of the possible defect states were analyzed by Density Functional Theory (DFT) calculations. We reveal the formation of deep interstitials defects (Cli) by Mn2+ doping. The depopulation of initial QDs exciton states is a competition between exciton-dopant energy transfer (ET) and defect trapping at an early time-scale (< 100 ps), which determines the final PLQY of the QDs. The present work establishes a robust material optimization guideline for all the emerging applications where high PLQY is essential.
关键词： photoluminescence,energy transfer,Mn-doped,CsPbCl3,DFT calculations,defect states,quantum dots
更新于2025-09-23 15:19:57
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Atomic Layer Deposition of Al <sub/>2</sub> O <sub/>3</sub> Using Aluminum Tri-Isopropoxide (ATIP): A Combined Experimental and Theoretical Study
摘要： The aluminum precursor plays a crucial role in the Al2O3 ALD process. Up to date, trimethyl aluminum (TMA) is one of the most widely used precursors in experimental and theoretical studies. However, its application at industrial scale can pose safety risks since it is pyrophoric and extremely reactive with water. Aluminum alkoxides offer a promising alternative, but have received far less attention. A combined theoretical and experimental investigation is carried out on the Al2O3 ALD process using aluminum triisopropoxide (ATIP) as a prototypical example of Al-alkoxide precursors. The experimental results pointed out that the thermal ALD process using ATIP and water has a maximal growth per cycle (GPC) of 1.8 ?/cycle at temperatures of 150°C to 175°C. Based on the in-situ mass spectrometry analysis and DFT calculations, the formation of the alumina film mainly occurs during the water pulse by ligand exchange reactions between water and adsorbed precursors, while during the ATIP pulse only adsorption of ATIP and/or its dissociation occur. Design of heteroleptic precursors containing alkoxide group as basic ligand is challenging, but greatly promising for future industrial scale Al2O3 ALD.
关键词： Al2O3,DFT calculations,Atomic Layer Deposition,Aluminum Triisopropoxide,Ligand Exchange Reactions
更新于2025-09-23 15:19:57
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Theoretical investigation on the kinetics and mechanism of the synthesis of fluorescent 3,8-disubstituted-3H-imidazo[4,5-a]acridine-11-carbonitriles
摘要： 3,8-Disubstituted-3H-imidazo[4,5-a]acridine-11-carbonitriles show very interesting optical properties. In some cases, they have higher quantum yields compared to well-known fluorescent dyes such as fluorescein. Hitherto, no detailed theoretical study has been reported on the mechanism of the synthesis of the titled compounds, hence an accurate and detailed theoretical investigation on the synthesis of these dyes is desirable. In this paper, density functional theory (DFT) methods have been employed to investigate the most reasonable mechanism in formation of these fluorophores. All species and related transition states were optimised and the relative energies of all species and the activation energies for all proposed mechanisms were obtained. Comparing the Ea values of all pathways reveals that intramolecular electrophilic aromatic substitution is the most plausible mechanism for the cyclisation reaction in the preparation of these dyes. Also, the effects of substituents in positions 3 and 8 were investigated and the results show that electron-donor substituents can reduce the activation energy for formation of the σ complex in the electrophilic aromatic substitution.
关键词： kinetics,intramolecular electrophilic aromatic substitution,thermodynamics,5-a]acridine,DFT calculations,imidazo[4,substituent effects
更新于2025-09-19 17:15:36
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Theoretical characterization of hexagonal 2D Be <sub/>3</sub> N <sub/>2</sub> monolayers
摘要： First-principles density functional theory (DFT) calculations are performed to assess the stability, geometric, mechanical, optical and electronic properties of monolayer graphene-like Be3N2. We find that Be3N2 is a large band gap semiconductor with small electron and hole effective masses, which may promote its use in nanoelectronic devices. Furthermore, the excellent thermal, dynamical, and mechanical stability makes it a material of the comparable caliber to that of graphene. In addition, the excellent electrochemical properties of Be3N2 makes it a unique material with the possible theoretical capacities of 974 mAh/g for Li, Na, and K. Moreover, Be3N2 can form bulk graphite-like layered structures with two different configurations, i.e. N2-N1 and N2-Be1. Finally, the derivatives of Be3N2 (Be3N2 nanoribbons) also possess direct band gaps which can finely be tuned to the desired level by geometry and morphology constraints. Based on these fascinating properties, Be3N2 and its derivatives can find a broad range of applications in nanoelectronics and battery technologies.
关键词： DFT calculations,Two-dimensional material,Nano-ribbons,Electrochemical properties,Electronic properties
更新于2025-09-19 17:15:36
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Deep Learning Spectroscopy: Neural Networks for Molecular Excitation Spectra
摘要： Deep learning methods for the prediction of molecular excitation spectra are presented. For the example of the electronic density of states of 132k organic molecules, three different neural network architectures: multilayer perceptron (MLP), convolutional neural network (CNN), and deep tensor neural network (DTNN) are trained and assessed. The inputs for the neural networks are the coordinates and charges of the constituent atoms of each molecule. Already, the MLP is able to learn spectra, but the root mean square error (RMSE) is still as high as 0.3 eV. The learning quality improves significantly for the CNN (RMSE = 0.23 eV) and reaches its best performance for the DTNN (RMSE = 0.19 eV). Both CNN and DTNN capture even small nuances in the spectral shape. In a showcase application of this method, the structures of 10k previously unseen organic molecules are scanned and instant spectra predictions are obtained to identify molecules for potential applications.
关键词： artificial intelligence,excitation spectra,organic molecules,DFT calculations,neural networks
更新于2025-09-19 17:15:36