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Lateral InSe p–n Junction Formed by Partial Doping for Use in Ultrathin Flexible Solar Cells
摘要： Two-dimensional InSe possesses good electrical conductivity, intrinsic and structural flexibility, high chemical stability, and a tunable band gap, enabling it to be a promising candidate for flexible and wearable solar cells. Here we construct a lateral p?n junction by partially doping molybdenum trioxide (MoO3) at the surface of the InSe monolayer. Our density functional theory calculations reveal that the strong hybridization between MoO3 and InSe induces a lateral built-in electric field in the partially doped substrate and promotes the effective separation of carriers. Under a large range of external stains, the doped InSe can maintain the direct band gap, and the lateral structure device exhibits power conversion efficiencies over 5% and high carrier mobility around 1000 cm2 V?1 s?1. In particular, a power conversion efficiency of 20.7% can be achieved with 10% compressive strain. The partially doped InSe monolayer is expected to be used as an ultrathin flexible solar cell.
关键词： lateral p?n junction,density functional theory,carrier mobility,flexible solar cells,power conversion efficiency,Two-dimensional InSe,molybdenum trioxide
更新于2025-09-11 14:15:04
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Tiny nano-scale junction built on B/N doped single carbon nanotube
摘要： The characteristic sizes of carbon nanotube (CNT) based devices are constantly reduced. However, the continuous miniaturization is still facing many problems and requires innovative ideas and structures. By regular doping Boron and Nitrogen atoms in a semiconducting single-wall carbon nanotube (SWCNT), we have constructed an nano-scale junction with rectifying characteristics. The I-V curve of our junction resembles the I-V curve of an ideal diode with a p-n junction. This junction channel is about 0.6nm wide and 3.4nm long, and the footprint is 5.1nm long. Under 0.5V bias, the junction has a leakage current of -8.81×10-3 μA, a rectifying ratio Ion/Ioff of 0.716×103, and a current density of 10.52 mA/μm. Also, our study shows that how different dopant distribution influence I-V curve. Such a nano-scale regular doping method is effective and important, compared with the traditional random doping method.
关键词： B/N doped junction,I-V curve,density functional theory,non-equilibrium Green’s function,carbon nanotube,regular doping,electronic transport
更新于2025-09-11 14:15:04
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Exciton Peierls mechanism and universal many-body gaps in carbon nanotubes
摘要： “Metallic” carbon nanotubes exhibit quasiparticle gaps when isolated from a screening environment. The gap-opening mechanism is expected to be of electronic origin, but the precise nature is debated. In this work, we show that hybrid density functional theory predicts a set of excitonic instabilities capable of opening gaps of the size found in experiment. The excitonic instabilities are coupled to vibrational modes and, in particular, the modes associated with the (cid:2) ? E2g and K ? A(cid:2) 1 Kohn anomalies of graphene, inducing Peierls lattice distortions with a strong electron-phonon coupling. In the larger tubes, the longitudinal optical phonon mode becomes a purely electronic dimerization that is fully symmetry conserving in the zigzag and chiral tubes, but breaks the symmetry in the armchair tubes. The resulting gaps are universal (i.e., independent of chirality) and scale as 1/R with tube radius.
关键词： exciton Peierls mechanism,electron-phonon coupling,many-body gaps,carbon nanotubes,hybrid density functional theory
更新于2025-09-11 14:15:04
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The mechanism of photocatalyst and the effects of co-doping CeO2 on refractive index and reflectivity from DFT calculation
摘要： In this paper, the structural, electronic and optical properties of (N, P), (N, S), (C, P) and (C, S) co-doped CeO2 are studied by using the method of density functional theory (DFT) + U method. The calculated lattice constant, the charge, the bond order, the cell volume and the bond length of CeO2 are consistent with previous experimental and theoretical results. For co-doped CeO2 systems, the calculated results show that the lattice constants, the bond order of CeeO as well as the cell volume increase, while the charge of Ce decrease. Due to co-doping, the energy gap (Eg) between valence band and conduction band becomes narrower than that of pure CeO2. Meanwhile, the electron structures of the co-doped CeO2 are changed, which may lead to transformation of optical properties. Nonmetallic atomic orbital (C 2p, N 2p, P 3p, S 3p) and metal atomic orbital (Ce 4f and 5d) are hybridized, except for the hybridization between Ce (4f and 5d) and O (2p). Compared with CeO2, Eg between Ce 4f and Ce 5d becomes smaller. Further, the optical absorption, refractive index and re?ectivity of them are investigated. The calculated results reveal that their absorption edges have a red shift. Co-doping enhances visible light photocatalytic activity, which is related to the transition of valence band → conduction band, and Ce 4f → Ce 5d. The co-doped CeO2 has high refractive index and re?ectivity. Therefore they may be becoming an important materials in single (or multilayered) optical coatings and optical re?ective pigments.
关键词： Refractive index,Density functional theory,Photocatalytic activity,Re?ectivity,Electronic transition
更新于2025-09-11 14:15:04
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First-principle calculation of the electronic structures and optical properties of the metallic and nonmetallic elements-doped ZnO on the basis of photocatalysis
摘要： In the present paper, the electronic structure and the optical properties of metallic and nonmetallic elements-doped ZnO were investigated based on the principle of photocatalysis by first-principle density functional theory. Element doping shortens the band gap of ZnO. Due to the p-type characteristics, Fe, Cu, B and N doping brings impurity states over the Fermi level of ZnO, resulting in the shortening of the band gap, extending the absorption and utilization of solar light and thus enhancing the photocatalytic properties of ZnO. However, no impurity states appear in the band gap of Cd- and S-doped ZnO due to the intrinsic doping of Cd and S. Further investigations indicate that different doping atoms can indeed alter the near-Fermi level density of states (DOS) of ZnO and their electronic structures via substitution of zinc and oxygen atoms. In addition, the optical properties of ZnO are improved after doped with different atoms by comparing with those of pure ZnO. Due to the difference of their outer shell electrons of the doped atoms, the optical absorption properties of the investigated materials are followed as the following order: Fe-/B-doped ZnO>Cu-/N-doped ZnO>Cd-/S-doped ZnO>pure ZnO.
关键词： Doped ZnO,Density functional theory (DFT),Photocatalysis,First principle calculation
更新于2025-09-11 14:15:04
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Accuracy of Partial Core Corrections Using Fourier Transforms in Pseudopotential–Density Functional Theory
摘要： Partial core corrections can be important in obtaining an accurate description of nonlinear exchange-correlation functionals and improving the transferability of pseudopotentials. We show that a widely used procedure, which calculates partial core charge density, ρcore partial, in Fourier space and then converts it to real space with fast Fourier transforms, can lead to sizable numerical errors of exchange-correlation potentials in the vacuum region. Such errors occur in modeling low-dimensional materials or surfaces with supercells. The loss of accuracy originates from the slow-decaying feature of core charge density in reciprocal space. Numerical errors on the order of 1 eV in the Kohn?Sham energies of unoccupied states can occur in pseudopotential?density functional calculations. The direct calculation of the partial core charge in real space can avoid the numerical errors caused by Fourier transforms.
关键词： pseudopotential?density functional theory,numerical errors,Fourier transforms,exchange-correlation potentials,partial core corrections
更新于2025-09-11 14:15:04
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Ultraviolet Absorption Spectra, Solvent Effect and Non-Linear Optical Properties of Tetrahydroxy-1,4-quinone Hydrate by Hartee-Fock and Density Functional Theory
摘要： In present work, the ultraviolet absorption spectrum of tetrahydroxy-1,4-quinone hydrate (TH,1,4-QH) has been carried out experimentally (in water, methanol dimethyl sulfoxide, acetonitrile and chloroform) and theoretically in the range 3500-2300 cm-1 in the solution phase. Predicted electronic absorption spectra from time dependent density functional theory (TD-DFT) calculation have been analyzed and compared with the experimental UV-visible spectrum. The effects of hydroxy group substituent in benzoquinone ring have been analyzed. The electronic properties such as excitation energy, wavelength corresponding to absorption maxima (λmax), oscillator strength (f), HOMO and LUMO energies are calculated by time-dependent density functional theory (TD-DFT) using HF/6-311++G(d,p) and B3LYP/6-311++G(d,p) as basis sets. The electric dipole moment (μ), α (polarizability) and β (first hyperpolarizability) have been computed to evaluate the NLO (non-linear optical) response of the investigated compound by Hartree-Fock (HF) and density functional theory (DFT) with B3LYP basis sets. Mulliken atomic charges of the atoms are calculated by DFT (B3LYP). In addition natural bond orbital (NBO) analysis has been done using TD-DFT with B3LYP/6-311++G(d,p) basis sets.
关键词： Tetrahydroxy-1,4-quinone hydrate,Density Functional Theory,NLO properties,Hartee-Fock,Ultraviolet spectrum
更新于2025-09-11 14:15:04
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Oxygen vacancy induced photoconductivity enhancement in Bi <sub/> 1- <i>x</i> </sub> Ca <i> <sub/>x</sub></i> FeO <sub/>3-δ</sub> nanoparticle ceramics: A combined experimental and theoretical study
摘要： Based on experimental and density functional studies, we show that tailoring of oxygen vacancies (OV) leads to large scale enhancement of photoconductivity in BiFeO3 (BFO). The OV concentration is increased by substituting an aliovalent cation Ca2+ at Bi3+ sites in the BFO structure. Furthermore, the OV concentration at the disordered grain boundaries can be increased by reducing the particle size. Photoconductivity studies carried out on spark plasma sintered Bi1-xCaxFeO3-δ ceramics show four orders of enhancement for x = 0.1. Temperature dependent Nyquist plots depict a clear decrease in impedance with increasing Ca2+ concentration which signi?es the role of OV. A signi?cant reduction in photoconductivity by 2 to 4 orders and a large increase in impedance of the air-annealed (AA) nanocrystalline ceramics suggest that OV at the grain boundaries primarily control the photocurrent. In fact, activation energy for AA samples (0.5 to 1.4 eV) is larger than the as-prepared (AP) samples (0.1 to 0.5 eV). Therefore, the room temperature J-V characteristics under 1 sun illumination show 2–4 orders more current density for AP samples. Density-functional calculations reveal that, while the defect states due to bulk OV are nearly ?at, degenerate, and discrete, the defect states due to surface OV are non-degenerate and interact with the surface dangling states to become dispersive. With large vacancy concentration, they form a defect band that enables a continuous transition of charge carriers leading to signi?cant enhancement in the photoconductivity. These studies reveal the importance of tailoring the microstructural features as well as the composition-tailored properties to achieve large short circuit current in perovskite oxide based solar cells.
关键词： density functional theory,BiFeO3,spark plasma sintering,Ca doping,oxygen vacancies,photoconductivity
更新于2025-09-11 14:15:04
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Trimer bonding states on the surface of the transition-metal dichalcogenide
摘要： We report a comprehensive study on the surface structural and electronic properties of TaTe2 at room temperature. The surface structure was investigated using both low energy electron diffraction intensity versus voltage and density functional theory calculations. The relaxed structures obtained from the two methods are in good agreement, which is very similar to the bulk, maintaining double zigzag trimer chains. The calculated density of states indicates that such structure originates from the trimer bonding states of the Ta dxz and dxy orbitals. This work will further provide new insights towards the understanding of the charge density wave phase transition in TaTe2 at low temperature.
关键词： surface structure,low energy electron diffraction,density functional theory,charge density wave,TaTe2
更新于2025-09-10 09:29:36
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Influence of Crystal Structure and 3d Impurities on the Electronic Structure of the Topological Material Cd3As2
摘要： This paper presents a theoretical study of the effects of crystal structure and Mn and Co substitutions for Cd on the electronic structure of the topological material Cd3As2. We have carried out density functional theory calculations of the band structure and density of states in tetragonal and cubic Cd3As2, as well as in Cd3 – xMnxAs2 and Cd3 – xCoxAs2 crystals. The results indicate that the band structure of the cubic Cd3As2 phase differs significantly from that of a Dirac semimetal, characteristic of the tetragonal phase. It has also been shown that, after Co substitution for 1/24 of the Cd atoms, the structure of the density of 3d electron states is similar to that of the density of states in the magnetic semiconductor Cd3 – xMnxAs2, with a characteristic minimum at the Fermi energy. At the same time, in the case of analogous Mn substitution for Cd, the density of d-electron states has no such minimum.
关键词： Mn,density functional theory (DFT) calculations,magnetic semiconductors,topological materials,Co,Cd3As2,Dirac semimetal,band structure,density of states (DOS)
更新于2025-09-10 09:29:36