In this study, we investigated a series of metal-free benzotriazole-based organic dyes. The geometries, electronic properties, light harvesting efficiency, and electronic absorption spectra of these dyes were studied using the density functional theory and time-dependent density functional theory. The optimised geometries indicate that these dyes are non-planar and thereby effectively inhibit close intermolecular π–π aggregation. The band gap of these dyes ensures a positive effect on the process of electron injection and dye regeneration. The band gap trend corroborates well with the predicted spectra data. Our theoretical calculations reveal that the designed metal-free organic dyes can be used as potential sensitisers for solar cells compared to the best known organic sensitiser (Y123) to date. 相似文献
A novel method for preparing flexible porous titania electrode from commercial TiO2 particles at low temperature for dye‐sensitized solar cells (DSSCs) was introduced. In this method, hydroxypropyl methyl cellulose (HPMC) as an additive was added to form a good‐quality TiO2/HPMC film on indium‐tin‐oxide‐coated polyethylene naphthalate flexible substrate (PEN/ITO). The additive was subsequently decomposed via the TiO2 photocatalytic degradation process under 365 nm UV‐light illumination at room temperature to form flexible multiporous TiO2 electrode film. Electrochemistry impedance spectroscopy (EIS) analysis indicated that the resistance of TiO2 film markedly decreased, and photocurrent–voltage curves showed that the photocurrent dramatically increased when the additive (HPMC) was removed from the flexible titania electrode film. The photocurrent conversion efficiency was estimated at 3.25% under 100 mW/cm2 illuminations using this flexible film as the DSSC photoanode.
We report results of combined experimental and theoretical studies of dye‐sensitized solar cells (DSSCs) using 5‐(4‐sulfophenylazo)salicylic acid disodium salt, known as Mordant Yellow 10 (MY‐10), as TiO2 sensitizer. We focus on a single dye but vary the solvent and the pH of the solution as well as the photoelectrode preparation conditions to determine the conditions for best photovoltaic conversion efficiency. We found experimentally that the efficiency, measured under standard air mass 1.5 global (AM 1.5G) conditions, was higher in solutions of ethanol than of water, but still small (up to 0.174%), although the fill factor (FF) was large (up to 0.73). Of the dyes in ethanol, MY‐10 in alkaline solution showed the best matching of the solar spectrum but displayed the lowest efficiency. Density functional theory (DFT) calculations provided the optimized geometry, electronic structure, and electronic spectrum of the dye in fully protonated as well as partially and totally deprotonated forms, in solution. The calculated optical spectra are consistent with the experimental data, with strong absorption in the visible range only for the alkaline dye solution. The low device efficiency is very likely related to the weak optical absorption in the visible range. The much higher photovoltaic conversion efficiency of the DSSCs fabricated using acid or roughly neutral pH solutions, corresponding to the protonated and partially deprotonated forms of MY‐10, respectively, is likely caused by the better alignment of the ground state of the dye with the redox level of the electrolyte. The decrease with pH of the dye solution of the short‐circuit current was linked to a weaker charge injection from the excited state of the dye to the conduction band of the oxide, which is correlated with the shifting of the excited state of the dye deeper into the CB edge of the semiconductor. The variation of the open‐circuit voltage with the pH of the solution was linked to the adjustment of the conduction band edge of TiO2, depending on the number of protons transferred from the dye to the oxide surface. Based on our results, we analyze the relative importance of the main criteria that should be met by a dye to be used in a DSSC. 相似文献
The geometric, energetic, electronic structures and optical
properties of ZnO nanowires (NWs) with hexagonal cross sections are
investigated by using the first-principles calculation of plane wave
ultra-soft pseudo-potential technology based on the density
functional theory (DFT). The calculated results reveal that the
initial Zn-O double layers merge into single layers after structural
relaxations, the band gap and binding energies decrease with the
increase of the ZnO nanowire size. Those properties show great
dimension and size dependence. It is also found that the dielectric
functions of ZnO NWs have different peaks with respect to light
polarization, and the peaks of ZnO NWs exhibit a significant
blueshift in comparison with those of bulk ZnO. Our results gives
some reference to the thorough understanding of optical properties
of ZnO, and also enables more precise monitoring and controlling
during the growth of ZnO materials to be possible. 相似文献
In the present work we use a series of Ti–Ru alloys, with minor amounts of Ru (0.01, 0.02, 0.05 and 0.2 at%) to grow anodic self‐organized Ru‐doped TiO2 nanotube layers. When used in dye‐sensitized solar cells (DSSCs), the nanotube layers with an optimum amount of Ru (0.02 at% Ru in the alloy) show a considerable increase in solar cell efficiency (η = 5.2%) under AM1.5 (100 mW/cm2) conditions compared with non‐doped TiO2 nanotubes (η = 4.3%).
P K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy is a powerful method for analyzing the electronic structure of organic and inorganic phosphorus compounds. Like all XANES experiments, P K‐edge XANES requires well defined and readily accessible calibration standards for energy referencing so that spectra collected at different beamlines or under different conditions can be compared. This is especially true for ligand K‐edge X‐ray absorption spectroscopy, which has well established energy calibration standards for Cl (Cs2CuCl4) and S (Na2S2O3·5H2O), but not neighboring P. This paper presents a review of common P K‐edge XANES energy calibration standards and analysis of PPh4Br as a potential alternative. The P K‐edge XANES region of commercially available PPh4Br revealed a single, highly resolved pre‐edge feature with a maximum at 2146.96 eV. PPh4Br also showed no evidence of photodecomposition when repeatedly scanned over the course of several days. In contrast, we found that PPh3 rapidly decomposes under identical conditions. Density functional theory calculations performed on PPh3 and PPh4+ revealed large differences in the molecular orbital energies that were ascribed to differences in the phosphorus oxidation state (III versus V) and molecular charge (neutral versus +1). Time‐dependent density functional theory calculations corroborated the experimental data and allowed the spectral features to be assigned. The first pre‐edge feature in the P K‐edge XANES spectrum of PPh4Br was assigned to P 1s → P‐C π* transitions, whereas those at higher energy were P 1s → P‐C σ*. Overall, the analysis suggests that PPh4Br is an excellent alternative to other solid energy calibration standards commonly used in P K‐edge XANES experiments. 相似文献
The perovskites are desirable materials for photovoltaic and other renewable green energy technologies. Lead-based perovskite solar cells (PSC) have recently gained considerable attention due to the abrupt rise in power conversion efficiency, but lead's well-known toxicity prevents its large-scale commercialization. One compelling option is Cs2TiBr6, which offers a nontoxic alternative. Herein, the electronic and optical characteristics of Cs2TiBr6 absorber material using density functional theory employing the WIEN2K tool are investigated. The energy band structure of Cs2TiBr6 shows an indirect bandgap of 2.2 eV. Additionally, optical properties are calculated, and the suitability of this material as an absorber for indoor and outdoor photovoltaic devices is investigated. The Cs2TiBr6 material has a peak absorption coefficient of 39.57 × 104 cm−1 and optical conductivity of 1.98 × 1015s−1, demonstrating its suitability as an absorber material. After that, a PSC is modeled using SCAPS-1D by using the computed parameters. The performance of the modeled perovskite is enhanced by optimization of various parameters, resulting in the achievement of a high-performance Cs2TiBr6-based PSC, boasting a power conversion efficiency of 19.9% for air mass AM1.5 G spectra and power conversion efficiency of 16.76% for light emitting diode and 17.18% for incandescent light for indoor light conditions. 相似文献
The yttrium (Y)‐doping effects on the electronic and optical properties of anatase TiO2 have been studied based on density functional theory calculations. Y substitution at Ti sites induces effective reduction in the band gap of anatase TiO2 and the Fermi level is shifted up in the band gap, this will be helpful in enhancing visible light absorption and electron‐hole pair separation, respectively. Optical properties show that Y doping shifts absorption edge of the TiO2 towards visible region and Y doping concentration of 4.16% have best visible light absorption among all models attributed to the optimal doping concentration. Our results may provide reasonable explanation for the experimental result.
Hole distributions introduced by a N doping atom in N‐doped TiO2 anatase nanoparticles are studied with first principles calculations. A nitrogen atom substitutes an oxygen atom in a TiO2 nanoparticle and introduces a hole in the particle. The empty state may be on the top of the valence band or inside the band gap as an impurity band. If the empty state is on the top of the valence band, the hole mainly distributes on the nitrogen atom and the two dangling atoms. The empty states on the dangling oxygen atoms introduced by the nitrogen doping atom can activate the dangling oxygen atoms and increase their oxidation ability. For example, the dangling oxygen atoms may oxidize absorbed small toxic molecules. The summation of the empty states on the nitrogen atom and the two dangling oxygen atoms is close to a constant and which is about one half of the total empty state of the particle for most of the substitutional configurations. Nitrogen atom can also generate an impurity band inside the band gap. This impurity band can make the N‐doped anatase particle absorb the visible lights. Eventually, the photo‐catalytic properties of anatase particles may be changed by the N‐doping processes. Most of the dopant formation energies in the particles are lower than that in the bulk. So, nitrogen doping process maybe easier in the small particle sample than in the bulk materials. 相似文献
