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Side chain effect on conjugated polymer/fullerene interfaces in organic solar cells: a DFT study
摘要： Considerable experimental research has been conducted on the influence of polymer alkyl side chains on the performance of bulk heterojunction organic solar cells. However, greater insight into the role of alkyl side chains in the polymer/fullerene interfacial regions is still needed. Using the dispersion-corrected density functional theory, we investigate the effect of alkyl side chains on the binding energies and electronic structures of various molecular pairings of fullerenes and monomers of organic copolymers (e.g. a pair of PC71BM and a monomer of copolymer PTB7 based on the thieno[3,4-b]thiophene/benzodithiophene repeat unit, PCBM and a copolymer PCDTBT based on 2,7-carbazole/dithienyl-2,1,3-benzothiazole and PC71BM and a copolymer PffBT4T-2OD based on difluorobenzothiadiazole/quaterthiophene). We find that the trends of the magnitudes of the binding energies vary with the lengths, types (branched or linear), and branching positions of alkyl side chains. Whenever possible, these results are compared with the efficiency trends of the corresponding organic solar cells. With the help of this comparison optimal side chain arrangements in bulk heterogeneous organic solar cells are identified. It is expected that these insights will aid in the production of more efficient organic photovoltaics.
关键词： binding energies,polymer alkyl side chains,organic solar cells,dispersion-corrected density functional theory,bulk heterojunction,electronic structures
更新于2025-09-12 10:27:22
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Methyl-terminated germanane GeCH3 synthesized by solvothermal method with improved photocatalytic properties
摘要： Owing to the tunable coordinated ligands in the covalently terminated (such as eH or other organic groups) group IV graphane analogues (GAs), i.e., silicane, germanane, stannanane, the electronic structures, stability and other related properties in these materials can be rationally tuned. In this work, the methyl-terminated germanane GeCH3, synthesized through a solvothermal process by using the Zintl phase CaGe2 crystal as precursors, is reported as a new class of covalently terminated photocatalyst. In contrast to the H-terminated germanane GeH, the GeCH3 photocatalyst shows enhanced photocatalytic performance during both hydrogen generation and the decomposition of Rhodamine B (RhB) dye under visible light illumination (λ ≥ 420 nm). The higher photocatalytic activity of GeCH3 can be attributed to its higher surface area, lower charge transfer resistance and preferable electronic structures comparing to GeH with H termination. Our work indicates 2D GAs could be an attractive platform for high e?cient photocatalysts with tunable properties, which could be potentially applied in many ?elds.
关键词： Electronic structures,Photocatalytic,Hydrogen,Covalently terminated,GeCH3
更新于2025-09-11 14:15:04
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Atomic and electronic structure of the Si(331)-(12 × 1) surface
摘要： We report on the investigation of the atomic and electronic structures of a clean Si(331)-(12 × 1) surface using a first-principles approach with both plane wave and strictly localized basis sets. Starting from the surface structure proposed by Zhachuk and Teys [Phys. Rev. B 95, 041412(R) (2017)], we develop significant improvements to the atomic model and localized basis set which are critical for the correct description of the observed bias dependence of scanning tunneling microscopy (STM) images. The size mismatch between the Si pentamers from the surface model and those seen by STM is explained within the context of the Tersoff-Hamann model. The energy barriers that separate different Si(331) buckled configurations were estimated, showing that the surface structure is prone to dynamic buckling at room temperature. It is found that empty electronic states on Si(331) are essentially localized on the pentamers with interstitials and under-coordinated Si sp2-like atoms between them, while filled electronic states are localized on under-coordinated Si sp3-like atoms and dimers on trenches. The calculated electronic density of states exhibits two broad peaks in the fundamental bandgap of Si: one near the valence band top and the other near the conduction band bottom. The resulting surface bandgap of 0.58 eV is in an excellent agreement with spectroscopy studies.
关键词： scanning tunneling microscopy,Si(331)-(12 × 1) surface,first-principles approach,electronic density of states,Tersoff-Hamann model,atomic and electronic structures,dynamic buckling
更新于2025-09-10 09:29:36
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Electronic structures and optical gain of dilute nitride GaAs nanowires
摘要： The electronic structures and optical gain of GaAs1%xNx nanowires are calculated via the band anticrossing model together with the eight-band k & p theory. We ?nd that the optical gain spectra show an obvious red shift, and the gain increases slightly with increasing nitrogen content. The transverse magnetic (TM) gain is approximately 8.5 times larger than the transverse electric (TE) gain when the radius R is 3 nm, which indicates that GaAs1%xNx nanowires can be used as TM linearly polarized lasers in the near-infrared range. However, when R is 6 nm, the TM gain approaches the corresponding TE gain. In this case, GaAs1%xNx nanowires are not suitable for linearly polarized lasers.
关键词： optical gain,electronic structures,GaAs nanowires,dilute nitride,band anticrossing model,k & p theory
更新于2025-09-10 09:29:36
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Extraction of tight binding parameters from in-situ ARPES on the continuously doped surface of cuprates
摘要： Recently we developed a technique of ozone/vacuum annealing to continuously change the doping level of the surface of Bi2Sr2CaCu2O8+x and measured a nearly whole superconducting dome on one surface by in-situ angle-resolved photoemission spectroscopy [arXiv: 1805.06450]. Here we study the evolution of the electronic structures of Bi2Sr2CaCu2O8+x using this technique together with tight binding fits. The tight binding parameters are extracted to study their evolution with doping.
关键词： cuprates,doping evolution,ARPES,electronic structures,tight binding
更新于2025-09-10 09:29:36
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Electronic Structures and Ferromagnetic Properties of 3d (Cr)-Doped BaSe Barium Selenide
摘要： In this study, we have employed the first-principle methods based on spin-polarized density functional theory to investigate the structural parameters, the electronic structures, and the half-metallic ferromagnetic behavior of chromium (Cr)-doped barium selenide (BaSe) such as Ba1 ? xCrxSe at concentrations x = 0.25, 0.5, and 0.75. The exchange and correlation potential is described by the generalized gradient approximation of Wu and Cohen (GGA-WC). The calculated structural parameters of BaSe are in good agreement with theoretical data. Our findings reveal that the p-d exchange coupling is ferromagnetic for Ba0.75Cr0.25Se and Ba0.5Cr0.5S, but it becomes anti-ferromagnetic for Ba0.25Cr0.75S. The electronic structures exhibit that the Ba1 ? xCrxSe materials for all concentrations are half-metallic ferromagnets with spin polarization of 100% and total magnetic moment per Cr atom of 4 μB. Therefore, the Ba1 ? xCrxSe compounds are suitable candidates for possible spintronics applications.
关键词： DFT,Cr-doped BaSe,Half-metallic ferromagnetic,Electronic structures
更新于2025-09-09 09:28:46
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Electronic structures and optical properties of IV A elements-doped 3C-SiC from density functional calculations
摘要： Electronic structures and optical properties of IV A elements (Ge, Sn and Pb)-doped 3C-SiC are investigated by means of the first-principles calculation. The results reveal that the structure of Ge-doped system is more stable with a lower formation energy of 1.249 eV compared with those of Sn- and Pb-doped 3C-SiC systems of 3.360 eV and 5.476 eV, respectively. Doping of the IV A elements can increase the band gap, and there is an obvious transition from an indirect band gap to a direct band gap. Furthermore, charge difference density analysis proves that the covalent order of bonding between the doping atoms and the C atoms is Ge–C > Sn–C > Pb–C, which is fully verified by population values. Due to the lower static dielectric constant, the service life of 3C-SiC dramatically improved in production practice. Moreover, the lower reflectivity and absorption peak in the visible region, implying its wide application foreground in photoelectric devices.
关键词： electronic structures,Silicon carbide,first-principles simulations,optical properties
更新于2025-09-09 09:28:46
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Effects of Surface Termination and Layer Thickness on Electronic Structures of LaNiO <sub/>3</sub> Thin Films
摘要： We investigate the e?ects of surface termination and layer thickness on the electronic structures of LaNiO3 thin ?lms on SrTiO3 substrate using ?rst-principles density-functional theory calculations. The NiO2-terminated ?lm with one unit cell thickness shows a pseudogap at the Fermi level owing to the negative charge transfer energy, whereas the 1.5-unit-cell-thick LaO-terminated ?lm exhibits an insulating gap of 1.0 eV as a result of the large exchange splitting. The metallic state is quickly restored for thicker ?lms with either NiO2 or LaO termination, resembling that in bulk nickelate. Our results indicate the strong dependence of the electronic properties on layer thickness and provide insightful information into the metal–insulator transition in LaNiO3 thin ?lms.
关键词： surface termination,electronic structures,layer thickness,LaNiO3 thin films,metal–insulator transition
更新于2025-09-04 15:30:14
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First-Principles Insights into the Oxidation States and Electronic Structures of Ceria-Based Binary, Ternary and Quaternary Oxides
摘要： Ceria and ceria-based materials have versatile technological and industrial applications, physically ascribed to the flexible fluctuation of Ce oxidation state between Ce4+ and Ce3+. A considerable multi-disciplinary research has been spent to obtain Ce oxidation state, the crucial quantity regarding the application; however, a rigorous and physically correct determination of oxidation state is still lacking. Here we conduct first-principles DFT + U calculations to unambiguously determine the physical oxidation state of Ce in ceria-based materials such as the homogenous CenO2n-2 (n = 7, 9, 10, 11, 12), ceria doped by multivalent Ti and V, Ce-Ti(V)-O ternary compounds, and Ce-Ti-V-O quaternary compounds. The results show that Ce oxidation state depends on the local structure and chemical surrounding: Oxygen vacancy facilitates the transition from Ce4+ to Ce3+, consistent with the localization of Ce 4f electrons; Ti and V with the 3d energy levels higher than 4f energy levels of Ce generally tend to reduce Ce4+ to Ce3+ particularly under the oxygen-deficiency condition. The atom-resolved determination of Ce oxidation states in the complicated compounds offers great promise for understanding the physical and chemical behavior of ceria-based materials, and for rational design of novel ceria-based materials for application potentials.
关键词： Ceria-based materials,First-principles calculations,Electronic structures,DFT + U,Oxidation states
更新于2025-09-04 15:30:14
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Occupied and unoccupied electronic structures of an L-cysteine film studied by core-absorption and resonant photoelectron spectroscopies
摘要： Unoccupied and occupied electronic structures of an L-cysteine film have been studied by absorption and resonant photoelectron spectroscopies. Core absorptions at S-L, C-K, N-K, and O-K levels indicate that the lower unoccupied states are predominantly composed of oxygen-2p, carbon-2p, and sulfur-4s+3d orbitals, while higher unoccupied states may be attributed dominantly to nitrogen-np (n ≥ 3), oxygen-np (n ≥ 3), and sulfur-ns+md (n ≥ 4, m ≥ 3) orbitals. Resonant photoelectron spectra at S-L23 and O-K levels indicate that the highest occupied state is originated from sulfur-3sp orbitals, while oxygen-2sp orbitals contribute to the deeper valence states. The delocalization lifetimes of the oxygen-1s and sulfur-2p excited states are estimated from a core-hole clock method to be about 9 ± 1 and 125 ± 25 fs, respectively.
关键词： resonant photoelectron spectroscopy,core-absorption,electronic structures,delocalization lifetime,L-cysteine
更新于2025-09-04 15:30:14