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Size-controlled excitonic effects on electronic and optical properties of Sb <sub/>2</sub> S <sub/>3</sub> nanowires
摘要： In this work, the electronic and optical properties of one-dimensional (1D) Sb2S3 nanowires (NWs) with different sizes are investigated using first-principles calculations. The indirect–direct band transition of Sb2S3 NWs can be tuned effectively by the NW size and various uniaxial strains. In the Sb2S3 NWs, the quantum confinement effects result in wider bandgaps while the significantly enhanced electron–hole interaction that is expected to produce excitonic bound states generates a bandgap narrowing. The exciton binding energies for the Sb2S3 NWs are predicted by the effective masses of electrons and holes to lie in the range of 0–1 eV, which are larger than that of bulk Sb2S3, suggesting that excitons in Sb2S3 NWs may bind possible defects to promote luminescence. The size-controlled absorption edge blueshift and redshift of Sb2S3 NWs suggest that Sb2S3 NWs may be promising in the applications of nanoscale light emitting devices.
关键词： optical properties,first-principles calculations,quantum confinement effects,light emitting devices,electronic properties,exciton binding energies,Sb2S3 nanowires
更新于2025-09-16 10:30:52
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Theoretical investigation of electronic bandgaps of semiconducting single-walled carbon nanotubes using semi-empirical self-consistent tight binding and <i>ab-inito</i> density functional methods
摘要： We perform a comprehensive theoretical study of electronic band gaps of semiconducting single-walled carbon nanotubes (SWNTs) with different sets of chiral indices using semi-empirical tight binding and density functional (DFT) based ab-initio methods. In particular, self-consistent extended Huckel (EH-SCF) and self-consistent Slater Koster (SK-SCF) tight binding models are used as semi-empirical methods, whereas the DFT based LDA-1/2 and Tran-Blaha (TB09) meta-GGA schemes are used as ab-initio methods. The calculations are performed for 1) (n, m) chiral SWNTs for which experimental optical gaps have been reported 2) (9, 0), (12, 0) and (15, 0) ‘metallic’ zigzag SWNTs for which small bad gaps have been reported 3) Pairs of SWNTs having same diameters but different chiral angles 4) (n, 0) zigzag SWNTs with ? ?n 30. From the comparison of bands gaps of tubes with same diameter, the electronic band gaps are found to vary with chiral angles with opposing trend as compared to that reported for experimental optical band gaps. This result may be expected to have important implications for self-energy corrections and/or exciton binding energies and their dependence on chiral angles. The hopping parameter g0 obtained from ?tting EH-SCF and SK-SCF bandgap data, is found to be in good agreement with that obtained from ?tting experimental data. In general, the band gap values of SWNTs computed using semi-empirical EH-SCF and SK-SCF methods are quite close (within ～ 5%) to those computed using DFT-based LDA-1/2 and TB09 meta-GGA methods. The results suggest that self-consistent semi-empirical methods can be expected to provide similar accuracy in results as that expected from more computationally challenging ab-intio DFT based LDA-1/2 and TB09 meta-GGA methods.
关键词： self-consistent tight binding method,semiconducting carbon nanotubes,electronic structure,first principles calculations
更新于2025-09-16 10:30:52
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On efficiency of earth-abundant chalcogenide photovoltaic materials buffered with CdS: the limiting effect of band alignment
摘要： Earth-abundant and environmentally-friendly Cu2–II–IV–VI4 (II = Sr, Ba; IV = Ge, Sn; VI = S,Se) are considered materials for the absorber layers in thin film solar cells. Attempts to understand and improve optoelectronic properties of these newly emerged absorbers resulted in an efficiency of 5.2% in less than two years. However, the energy band alignment at the buffer/absorber interface has not been studied yet; an information which is of crucial importance for designing high performance devices. Therefore, current study focuses on the band offsets between these materials and the CdS buffer. Using first-principles calculations, band discontinuities are calculated at the buffer/absorber interface. The results yield a type-II band alignment between all Cu2–II–IV–VI4 absorbers and CdS, hence a negative DEc. Adoption of a negative DEc (cliff-like conduction band offset) at the buffer/absorber interface, however, gives rise to low open circuit voltage and high interface-related recombinations. Therefore, it is necessary to search for an alternative buffer material that forms a type-I band alignment with these absorbers, where the conduction band minimum and the valence band maximum are both localized on the absorber side.
关键词： buffer/absorber interface,earth-abundant chalcogenides,band alignment,first-principles calculations
更新于2025-09-16 10:30:52
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Theoretical Study of GaN/BP van der Waals Nanocomposites with Strain-Enhanced Electronic and Optical Properties for Optoelectronic Applications
摘要： Construction of van der Waals (vdW) nanocomposites can advance two-dimensional (2D) materials with desired properties and significantly widen their applications. Based on first-principles calculations, we verify that a gallium nitride/boron phosphide (GaN/BP) vdW nanocomposite is a direct-gap semiconductor with type-I band alignment. The nanocomposite shows significant optical properties in the visible and near-ultraviolet regions. Additionally, the bandgap, band edge positions, and optical absorption of the GaN/BP nanocomposite can be tuned by in-plane biaxial strains. A biaxial tensile strain with a strength of 3% can induce the type-II band alignment in the GaN/BP nanocomposite, which results in effective separation of the photo-generated charge carriers. Meanwhile, the application of biaxial strain can also significantly enhance the optical absorption of the GaN/BP nanocomposite in the near-infrared and visible regions. Furthermore, we show that the adjustment of interlayer coupling is also an effective way to modulate the electronic and optical properties of the GaN/BP nanocomposite. Our studies reveal the potential application of the GaN/BP nanocomposite in optoelectronic devices.
关键词： first-principles calculations,optical absorption,strain engineering,band structure,GaN/BP nanocomposite
更新于2025-09-16 10:30:52
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LiZnN filled-tetrahedral compound: A first-principles study of the electronic, optical and effective mass properties
摘要： In the present contribution, first-principles calculation, based on the density functional theory using full-potential linearized augmented plane wave method, is applied to investigate the electronic structure and optical properties of LiZnN filled-tetrahedral compound. It is known that the density functional theory, using the generalized gradient approximation, underestimates the bandgap energy. Therefore, to overcome such difficulty, the regular and non-regular Tran-Blaha modified Becke-Johnson method has been used to obtain more accurate estimations of the compound properties and the bandgap energy. The non-regular Tran-Blaha modified Becke-Johnson method gives a significant improvement in the accuracy of the energy gap, in close agreement with the experimental results. Such a result is used to provide the Luttinger parameters, the dielectric constant and the effective masses. Moreover, an analysis of the electronic band structure and optical properties were carried out.
关键词： LiZnN,electronic structure,first-principles calculations
更新于2025-09-16 10:30:52
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Band offset modulation in Si-EuO heterostructures via controlled interface formation
摘要： Combining first-principles calculations and experiment, we investigate the atomic and electronic structure of the Si/EuO interface. We consider the thermodynamic stability of interface structures with different levels of oxidation to identify the most probable configuration. By comparing the calculated band alignment and core-level shifts with measured values, we validate the theoretically constructed interface model. We find that the band offset can be tuned by altering the relative energy positions of the Si and EuO conduction bands via interface oxidation, which can be used to tune this materials system for specific applications in spintronics.
关键词： XPS,band alignment,first-principles calculations,Si/EuO interface,spintronics
更新于2025-09-12 10:27:22
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Interfacing boron monophosphide with molybdenum disulphide for an ultrahigh performance in thermoelectrics, 2D excitonic solar cells and nanopiezotronics
摘要： Stable ultrathin 2D van der Waals (vdW) heterobilayer, based on the recently synthesized boron monophosphide (BP) and the widely studied molybdenum disulphide (MoS2), has been systematically explored for the conversion of waste heat, solar energy and nanomechanical energy into electricity. It shows a gigantic figure of merit (ZT) > 12 (4) for p (n)-type doping at 800 K, which is the highest ever reported till date. At room temperature (300 K), ZT reaches 1.1 (0.3) for p(n)-type doping which is comparable to experimentally measured ZT=1.1 on PbTe-PbSnS2 nanocomposite at 300 K. While it outweighs the Cu2Se-CuInSe2 nanocomposite (ZT=2.6 at 850 K) and the theoretically calculated ZT = 7 at 600 K on silver halides. Lattice thermal conductivity (???? ~ 49 Wm-1K-1) calculated at room temperature is lesser than that of black phosphorene (78 Wm-1K-1) and arsenene (61 Wm-1K-1). The nearly matched lattice constants in the commensurate lattices of the constituent monolayers helps to preserve the direct band gap at the K point in the type II vdW heterobilayer of MoS2/BP, where BP and MoS2 serve as donor and acceptor materials respectively. An ultrahigh carrier mobility ~ 20 × 103 cm2V-1s-1 is found, which exceeds that of previously reported transition metal dichalcogenide based vdW heterostructures. The exciton binding energy (0.5 eV) is close to that of MoS2 (0.54 eV) and C3N4 (0.33 eV) single layers. The calculated power conversion efficiency (PCE) in monolayer MoS2/BP heterobilayer exceeds 20%. It surpasses the efficiency in MoS2/p-Si heterojunction solar cells (5.23%) and competes with the theoretically calculated ones, listed in the manuscript. Furthermore, high optical absorbance (~105 cm-1) of visible light and small conduction band offset (0.13 eV) makes MoS2/BP very promising in 2D excitonic solar cells. Out-of-plane piezoelectric strain coefficient, ??33 ~ 3.16 pm/V, is found to be enhanced four-fold (~14.3 pm/V) upon applying 7% vertical compressive strain on the heterobilayer, which corresponds to ~1 kBar of hydrostatic pressure. Such a high out-of-plane piezoelectric coefficient, which can tune top-gating effects in ultrathin 2D nanopiezotronics, is a relatively new finding. As BP has been synthesized recently, experimental realization of the multifunctional, versatile MoS2/BP heterostructure would be highly feasible.
关键词： first-principles calculations,piezoelectricity,thermoelectricity,solar energy conversion efficiency,excitonic solar cells
更新于2025-09-12 10:27:22
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The influence of edge structure on the optoelectronic properties of Si <sub/>2</sub> BN quantum dot
摘要： In recent work, we have investigated the electronic and optical properties of pristine and functionalized Si2BN quantum dots (QDs) using first-principles calculations. Due to the edge functionalization, Si2BN QDs have binding energies of ?0.96 eV and ?2.08 eV per hydrogen atom for the adsorption of single and double hydrogen atoms, respectively. These results reveal the stability and the bonding nature of hydrogen at the edges of Si2BN QD. In particular, the charge transfer between hydrogen and other atoms is explicitly increased. The electronic band structure of pristine Si2BN QD shows a metallic behavior with a finite number of electronic states in the density of states at the Fermi level. The frequency-dependent optical properties, such as refractive index, extinction coefficient, absorption coefficient, electron energy loss spectra, and reflectivity, are computed for both the parallel and perpendicular components of electric field polarization. The higher absorption was found in the infrared regime. The present study shows that the functionalization of Si2BN QD by two hydrogen atoms is energetically stable. It offers a promising application of Si2BN QD, which can be used in optical nanodevices such as photodetectors and biomedical imagination.
关键词： optical properties,Si2BN quantum dot,first-principles calculations,metallic behavior,electronic properties,hydrogen functionalization,infrared absorption,optical nanodevices
更新于2025-09-12 10:27:22
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Monolayer HfTeSe4: A promising two-dimensional photovoltaic material for solar cells with high efficiency
摘要： Currently, atomically thin materials with high photovoltaic performance are urgently needed for applications in solar cells. Herein, by using first-principles calculations, we propose an excellent two-dimensional photovoltaic material, monolayer HfTeSe4, which can be exfoliated feasibly from its layered bulk. It behaves the semiconductor character with a moderate direct gap of 1.48 eV and exhibits remarkable absorbance coefficient of ~105 cm-1 in visible-light region. Meanwhile, monolayer HfTeSe4 shows ultrahigh photocurrent and a long carrier recombination life-time. And strain engineering can further modulate the recombination time of carriers. Moreover, the heterostructure between HfTeSe4 and Bi2WO6 is proposed as potential solar cells with the solar conversion efficiency up to ~20.8%. These extraordinary properties combined with its experimental feasibility makes monolayer HfTeSe4 particularly promising for photovoltaic device applications.
关键词： absorbance coefficient,solar conversion efficiency,carrier recombination,photovoltaic,first-principles calculations,photocurrent
更新于2025-09-12 10:27:22
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Manganese doping mechanism in a CsPbI <sub/>2</sub> Br photovoltaic material: a first-principles study
摘要： As a light absorbing material of perovskite solar cells, Mn-doped CsPbI2Br has a better phase stability than the undoped one. In order to deeply understand the doping mechanism of Mn, the effect of substitutional and interstitial Mn doping on the structural, electronic and optical properties of CsPbI2Br has been investigated by first-principles calculations based on density functional theory. It is found that the binding energy of both the substitutional and the interstitial Mn-doped CsPbI2Br is negative and the binding energy difference between them is only 2.8 meV, which indicates that both the substitutional and the interstitial doping structures should be stable for Mn-doped CsPbI2Br and the latter is slightly preferred over the former due to the lower binding energy. The lattice parameters of CsPbI2Br change oppositely for two Mn-doping cases. Based on the comparative analysis of the electronic structures for CsPbI2Br and Mn-doped CsPbI2Br, we found that the substitutional doping of Mn introduces intermediate level, making CsPbI2Br an intermediate band semiconductor; for the interstitial bands near the Fermi Mn-doped CsPbI2Br the Fermi level enters conduction bands, making it an n-type semiconductor material with enhanced conductivity. The complex dielectric function and the absorption spectrum of Mn-doped and undoped CsPbI2Br were calculated and are basically consistent with the experimental results.
关键词： first-principles calculations,density functional theory,electronic and optical properties,perovskite solar cells,Mn-doped CsPbI2Br
更新于2025-09-12 10:27:22