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Analogous to conventional carbon nanotubes, single-walled, chiral, γ-graphyne nanotubes (C-γGyNTs) are modeled based on the synthesized 2D γ-graphyne motif, and their electronic properties are investigated via density-functional tight-binding calculations for the first time. The resulting γGyNTs are predicted to be excellent semiconductors with moderate bandgaps ranging from 1.291 eV to 1.928 eV. In addition, the bandgaps of zigzag γGyNTs and armchair γGyNTs show damped oscillatory behaviour, while those of C-γGyNTs do not show any chirality- or diameter-dependent oscillatory behaviour. Interestingly, it is revealed that the (2a, m)-γGyNTs, where a is a positive integer, have nearly identical bandgap values, which provides a fresh method of bandgap manipulation for semiconductor devices that has not yet been reported. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

First principles calculations have been performed to investigate the structural, electronic, and optical properties of germanene/MoS2 heterostructures. The results show that a weak van der Waals coupling between germanene and MoS2 layers can lead to a considerable band-gap opening (53 meV) as well as the preserved Dirac cone with a linear band dispersion of germanene. The applied external electric filed can not only enhance the interaction strength between two layers, but also linearly control the charge transfer between germanene and MoS2 layers, and consequently lead to a tunable band gap. Furthermore, the reduction in the optical absorption intensity of the heterostructures with respect to the separated monolayers has been predicted. These findings suggest that the Ge/MoS2 hybrid can be designed as the device where both finite band gap and high carrier mobility are required. [ABSTRACT FROM AUTHOR]

Abstract: Coumarin dyes containing a low band-gap chromophore of benzothiadiazole, which comprises a coumarin moiety as the electron donor and a cyanoacrylic acid moiety as electron acceptor in D–A–π–A system, were developed to use in dye-sensitised solar cells (DSSCs). The introduction of the benzothiadiazole unit into the molecular framve distinctly narrowed the band-gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), so that the absorption peak was red-shifted. As a result, a solar cell based on the HKK-CM4 sensitiser showed better photovoltaic performance with a J SC of 14.3mAcm−2, a V OC of 0.58V, and an FF of 0.72, corresponding to an overall conversion efficiency η of 5.97% under standard AM 1.5 irradiation. [Copyright &y& Elsevier]

[Display omitted] A novel all-carbon material with quasi 2D character, supertetrahedraphene, was proposed using carbon tetrahedron as the starting material. The geometry and electronic properties were investigated via density functional theory (DFT) calculations. Supertetrahedraphene was confirmed to be an energetically meta-stable and dynamically stable semiconductor with an indirect band gap of 2.80 eV. An acetylenic linkage (C C) was inserted to change the height of supertetrahedraphene, resulting in a new sp + sp 3 hybrid system. Insertion of C C can further stabilize supertetrahedraphene and transform it to a semiconductor with direct band gaps. These band gaps steadily decrease as the number of C C increases, and the supertetrahedraphene is predicted to be metallic if the C C is of sufficient length. Our results suggest a strategy to design novel carbon materials with desired properties. [ABSTRACT FROM AUTHOR]