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Electrically controlled dielectric band gap engineering in a two-dimensional semiconductor
摘要： The emergent class of atomically thin two-dimensional (2D) materials has opened up completely new opportunities for manipulating electronic quantum states at the nanoscale. Here we explore the concept of dielectric band gap engineering, i.e., the controlled manipulation of the band gap of a semiconductor via its dielectric environment. Using first-principles calculations based on the GW self-energy approximation we show that the band gap of a two-dimensional (2D) semiconductor, such as the transition metal dichalcogenides, can be tuned over several hundreds of meV by varying the doping concentration in a nearby graphene sheet. Importantly, these significant band gap renormalizations are achieved via nonlocal Coulomb interactions and do not affect the structural or electronic integrity of the 2D semiconductor. We investigate various heterostructure designs, and show that, depending on the size of the intrinsic dielectric function of the 2D semiconductor, the band gap can be tuned by up to 1 eV for graphene carrier concentrations reachable by electrostatic doping. Our work provides opportunities for electrically controllable band gap engineering in 2D semiconductors.
关键词： GW self-energy approximation,transition metal dichalcogenides,graphene,two-dimensional semiconductor,dielectric band gap engineering
更新于2025-09-23 15:19:57
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Efficiency Limits of Underwater Solar Cells
摘要： Operation of underwater vehicles and autonomous systems is currently limited by the lack of long-lasting power sources. These systems could potentially be powered using underwater solar cells, but the material requirements to achieve their full potential are not well understood. Using detailed-balance calculations, we show that underwater solar cells can exhibit efficiencies from ~55% in shallow waters to more than 65% in deep waters, while maintaining a power density >5 mW cm?2. We show that the optimum band gap of the solar cell shifts by ~0.6 eV between shallow and deep waters and plateaus at ~2.1 eV at intermediate depths, independent of geographical location. This wide range in optimum band-gap energies opens the potential for a library of wide-band-gap semiconductors to be used for high-efficiency underwater solar cells. Our results provide a roadmap for proper choice of underwater solar cell materials, given the conditions at points of use.
关键词： wide-band-gap semiconductors,detailed-balance calculations,efficiency limits,power density,underwater solar cells
更新于2025-09-23 15:19:57
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Mechanically Robust All-Polymer Solar Cells from Narrow Band Gap Acceptors with Hetero-Bridging Atoms
摘要： A series of polymer acceptors PF2-DTC, PF2-DTSi, and PF2-DTGe with identical molecular backbone but different central bridging atoms in tricyclic-fused donor units were developed. In all-PSCs, the PF2-DTSi-based blend film exhibited excellent mechanical robustness with an impressively high PCE of up to 10.77%. Moreover, the flexible solar cell based on this blend retained >90% of its initial PCE after bending and relaxing 1,200 times at a bending radius of ~4 mm.
关键词： Mechanical robustness,All-polymer solar cells,Narrow band gap acceptors,Power conversion efficiency,Hetero-bridging atoms
更新于2025-09-23 15:19:57
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High-Performance UVa??Vis Photodetectors Based on a Lead-Free Hybrid Perovskite Crystal (MV)[SbI <sub/>3</sub> Cl <sub/>2</sub> ]
摘要： Low-dimensional lead-free organic?inorganic hybrid perovskites have gained increasing attention as having low toxicity, ease of processing, and good optoelectronic properties. Seeking for lead-free and narrow band gap organic?inorganic hybrid perovskites are of great importance for the development and application of photoelectric materials. Here, we reported a Sb-based organic?inorganic hybrid perovskite (MV)[SbI3Cl2], which has one-dimensional inorganic frameworks of the I-sharing double octahedra. (MV)[SbI3Cl2] shows a narrow direct band gap of 1.5 eV, and displays obvious photoresponse for the 532 nm light with rapid response speed of trise = 0.69 s, tdecay = 0.28 s. With an illumination power of 5 mW and a 50 V bias, the responsivities (R) and external quantum e?ciency (EQE) for (MV)[SbI3Cl2] photodetector under 532 nm laser are 29.75 mA/W and 6.69% respectively. This Sb-based halide double perovskite material will provide an alternative material for photodetector devices.
关键词： organic?inorganic hybrid perovskites,Sb-based,narrow band gap,photodetectors,lead-free
更新于2025-09-23 15:19:57
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[IEEE 2018 International Semiconductor Conference (CAS) - Sinaia, Romania (2018.10.10-2018.10.12)] 2018 International Semiconductor Conference (CAS) - Substrate Effect on the Morphology and Optical Properties of ZnO Nanorods Layers Grown by Microwave-Assisted Hydrothermal Method
摘要： The substrate effect on the morphology and optical properties of zinc oxide nanorods synthesized by microwave-assisted hydrothermal method have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-VIS-NIR optical absorption and reflecting spectroscopy. The band gap energy of the investigated samples was calculated from absorbance spectra in the (200-1100) nm wavelengths range.
关键词： optical properties,ZnO nanorods,band gap energy,microwave-assisted hydrothermal synthesis,morphology
更新于2025-09-23 15:19:57
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Influence of Precursor Concentration on Structural, Morphological and Optical Properties of Hematite (α-Fe <sub/>2</sub> O <sub/>3</sub> ) Nanoparticles
摘要： Background: We report for the first time that there is a considerable effect on the morphology and optical properties of hematite (α-Fe2O3) nanoparticles by varying the precursor concentrations from 1mmol to 3mmol. The nanoparticles were synthesized by combustion route using ferric nitrate, citric acid and ammonia as precursors at an annealing temperature range of 6000C. Phase purity, morphological studies and optical properties of the products were studied by powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Raman spectroscopy and UV Visible spectroscopy. The as-synthesized hematite nanoparticles have a mesoporous granular and somewhat spherical structure with a bulk density ranging from 0.11 to 0.59gmcm-3. Conclusion: The band gap of the as-synthesized α-Fe2O3 nanoparticles decreases from 1.96eV-1.77eV with the decrease in the precursor concentration. Raman spectroscopy confirmed the formation of a hematite phase of iron oxide nanoparticles. Practical percentage yield of the products increased from 47% to 65% with decrease in precursor concentrations.
关键词： α-Fe2O3 nanoparticles,band gap,Optical properties,morphological studies,bulk density,Combustion synthesis
更新于2025-09-23 15:19:57
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Tailoring properties of hybrid perovskites by domain-width engineering with charged walls
摘要： Charged ferroelectric domain walls are fascinating electrical topological defects that can exhibit unusual properties. Here, in the search for novel phenomena, we perform and analyze first-principles calculations to investigate the effect of domain width on properties of domains with charged walls in the photovoltaic material consisting of methylammonium lead iodide hybrid perovskite. We report that such domains are stable and have rather low domain wall energy for any investigated width (that is, up to 13 lattice constants). Increasing the domain width first linearly decreases the electronic band gap from ?1.4 eV to about zero (which therefore provides an efficient band-gap engineering), before the system undergoes an insulator-to-metal transition and then remains metallic (with both the tail-to-tail and head-to-head domain walls being conductive) for the largest widths. All these results can be understood in terms of: (i) components of polarization along the normal of the domain walls being small in magnitude; (ii) an internal electric field that is basically independent of the domain width; and (iii) rather negligible charge transfer between walls. These findings deepen the knowledge of charged ferroelectric domain walls and can further broaden their potential for applications, particularly in the context of halide perovskites for photovoltaics.
关键词： charged ferroelectric domain walls,hybrid perovskites,photovoltaic materials,band-gap engineering,insulator-to-metal transition
更新于2025-09-23 15:19:57
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Nitrogen pair-induced temperature insensitivity of the band gap of GaNSb alloys
摘要： The temperature dependence of the band gap of GaNxSb1-x films with x ≤ 1.3% has been studied in the 1.1–3.3 μm (0.35–1.1 eV) range using infrared absorption spectroscopy between 4.2 and 300 K. As with other dilute nitride semiconductors, the temperature dependence of the band gap is reduced by alloying with nitrogen when compared to the host binary compound. However, for GaNSb, the smallest variation of the band gap with temperature is observed for samples with the lowest N content for which the band gap is almost totally insensitive to temperature changes. This contrasts with the more widely studied GaNxAs1-x alloys in which the band gap variation with temperature decreases with increasing N content. The temperature-dependent absorption spectra are simulated within the so-called band anticrossing model of the interaction between the extended conduction band states of the GaSb and the localized states associated with the N atoms. The N next-nearest neighbor pair states are found to be responsible for the temperature insensitivity of the band gap of the GaNSb alloys as a result of their proximity to the conduction band edge giving them a more pronounced role than in GaNAs alloys.
关键词： band anticrossing,GaSb,dilute nitride,GaNSb,band gap
更新于2025-09-19 17:15:36
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Optical band gap and dielectric abnormality in (Sr, Ce, Zr)TiO3 composite ceramics sintered in nitrogen
摘要： The crystal-chemical structure, band gap-grain structure and dielectric properties of (1?x)SrTiO3-xCe0.95Zr0.05O2 [(Sr,Ce,Zr) TiO3, for x = 0.0, 0.3 and 0.4] ceramics were investigated. Samples with 0.3 ≤ x ≤ 0.4 appeared cubic by X-ray diffraction (XRD), however, splitting of the peaks along with Rietveld refinement indicated tetragonal structure. The change in the band gap energy with Ce(x) have been investigated and are related to variation in the grain size, activation energy and octahedral tilting. The reduction in band gap energy with Ce0.95Zr0.05O2 ions (x = 0.4) is attributed to the widening of conduction band with octahedral tilting. The absence of TO2 (175 cm?1) mode while the existence of TO4 (521.72 cm?1) mode has been considered as sign of relaxor-like-dielectric behavior. The ε′?T curve and the P–E loop analysis confirms that there is no signature of the ferroelectric phase in all samples. Base on the X-ray photoelectrons spectroscopy (XPS) and high temperature ac conductivity analysis, the dielectric anomalies were due to the formation of lattice defects and defect dipoles ( Ti4+ ? e? ? V ?? o ) generated by the Ti3+ ions and ionized oxygen vacancies.
关键词： Crystal-band gap structure,Dielectric properties,Oxygen vacancies
更新于2025-09-19 17:15:36
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Effect of Strontium Doping on the Band Gap of $$\hbox {CeO}_{2}$$ CeO 2 Nanoparticles Synthesized Using Facile Co-precipitation
摘要： Pure, 3 mol% and 5 mol% Sr-doped cerium oxide nanoparticles were synthesized by facile aqueous co-precipitation method using cerium nitrate hexahydrate and strontium chloride hexahydrate as the precursors without using any capping agent. The synthesized material was characterized by XRD, SEM, EDX, TEM, Raman spectroscopy and UV–Vis spectroscopic techniques. SEM analysis showed agglomeration of the particles. The Debye–Scherrer analysis revealed ?uorite structure of the synthesized material with crystallite size in 6–10 nm range. TEM con?rmed the spherical morphology of the particles and particle size distribution in the range of 5–8 nm. UV–Vis spectroscopic study revealed that Sr-doping led to increase in the band gap from 3.2 to 3.7 eV and shifting of absorption edge to the lower wavelength. The blue shift in the band gap with the dopant concentration shows that the band gap of doped cerium oxide nanoparticles can be tuned with variation in the dopant concentration.
关键词： Sr-doped cerium oxide,Blue shift,Band gap
更新于2025-09-19 17:15:36