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Micro/nanoscale mesoporous Nb2O5 particles: Effect of synthesis conditions and doping with N, C, or S on their properties
摘要： A simple methodology was designed to obtain mesoporous niobium pentoxide (Nb2O5) solids functionalized with nitrogen, carbon, or sulfur. Dopant precursors were urea (N), citric acid (C) and thiourea (S). The doped solids were characterized using IR, Raman and diffuse reflectance UV–Vis spectroscopies, powder X-ray diffraction, adsorption–desorption isotherms, transmission electron and scanning electron microscopies. Depending on the amount of surfactant (cetyltrimethyl ammonium bromide — CTAB) used during synthesis, the solid presented mainly an orthorhombic crystal structure or an amorphous phase (for the sample with 0.25 mol/L CTAB). The adsorption–desorption isotherms of the synthesized solids showed hysteresis loops ( H1 andH4 types) characteristic of mesoporous solids, while transmission electron micrographs showed a disordered structure of pore channels known as ‘‘wormholes’’. There was considerable interaction between the dopant anion (mainly N and S) and the solid surface, generating new surface chemical species that clogged the pores, reducing specific surface and pore volume. The doped mesoporous Nb2O5 materials were polycrystalline, formed by primary monocrystalline particles of nanometric size (10–20 nm). Doping with N, C and S caused an important effect on the absorption of visible light, reducing the band gap energy value to 2.95 eV when doped with N, and to ～2.8 eV with S, relative to that of the undoped sample (3.03 eV). This result is important considering the potential use of mesoporous Nb2O5 materials in photocatalytic processes.
关键词： N, C and S dopants,Synthesis,Nanomaterials,Characterization,Mesoporous Nb2O5
更新于2025-09-10 09:29:36
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Dopants Control of Electron-Hole Recombination in Cesium-Titanium Halide Double Perovskite by Time Domain Ab Initio Simulation: Co-Doping Supersedes Mono-Doping
摘要： Using nonadiabatic (NA) molecular dynamics combined with time-domain density functional theory, we simulate electron-hole recombination in pristine and doped inorganic Pb-free double perovskite Cs2TiBr6. We show that replacing the titanium and/or bromine with silicon and/or chlorine extends the charge carrier lifetime. Importantly, dopants avoid deep traps despite they do not change the fundamental bandgap of Cs2TiBr6, they decrease the NA electron-phonon coupling and accelerate decoherence, arising from the reduced overlap of electron and hole wave functions as well as fast phonon modes induced by light dopants respectively, suppressing electron-hole recombination. More importantly, co-doping can reduce the formation energy of silicon and achieve higher doping concentration, potentially increasing the lifetime further. Our study suggests a rational strategy to reduce energy losses by co-doping in design of high performance all-inorganic Pb-free perovskite solar cells.
关键词： Co-doping,Electron-Hole Recombination,Mono-doping,Energy Conversion and Storage,Cesium-Titanium Halide Double Perovskite,Plasmonics and Optoelectronics,Time Domain Ab Initio Simulation,Dopants Control
更新于2025-09-10 09:29:36
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The Role of Weak Molecular Dopants in Enhancing the Performance of Solution-Processed Organic Field-Effect Transistors
摘要： Molecular doping is an effective method to enhance the charge carrier density for reducing the contact resistance and improving the charge mobility in organic field-effect transistors (OFETs). Previous reports mainly focus on the strong dopants with the EAdopant > IEOSC (p-type) or IEdopant < EAOSC (n-type) to enable the efficient charge transfer (EA: electron affinity; IE: ionization energy; OSC: organic semiconductor). However, the effects of weak dopants on the OFET performance of OSC are rarely investigated. Thus, in this study, it is demonstrated that two new fluorinated compounds (Tetrafluorophthalonitrile (TFP) and Octafluoronaphthalene (OFN)) can act as weak dopants in thin film of TIPS-Pentacene (TIPS). Although they exhibit unmatched EAs (3.45 eV for TFP and 3.44 eV for OFN) compared to the IE (5.17 eV) of the host TIPS, they still can fulfill the p-type doping with the OSC matrix. Systematic structural and electrical characterization reveals the important role of the formed charge-transfer interaction and the improved crystallinity in enhancing the carrier mobility. The doped poly(3-hexylthiophene) is also investigated to confirm the universality of the weak dopants. The study should provide a new thought for the exploitation of novel planar soluble weak dopants in OFETs.
关键词： solution-processed organic field-effect transistors,molecular doping,weak dopants
更新于2025-09-09 09:28:46
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Trap-Mediated Two-Step Sensitization of Manganese Dopants in Perovskite Nanocrystals
摘要： Halide perovskite nanocrystals hold promise for printable optoelectronic and photonic applications. Doping enhances their functionalities and is being investigated for substituting lead with environmentally friendlier elements. The most investigated dopant is Mn2+ that acts as a color center sensitized by the host excitons. The sensitization mechanism is far from understood and no comprehensive picture of the energy-transfer process has been proposed. Similarly, the role of shallow states - particularly abundant in defect tolerant materials - is still unknown. Here, we address this problem via spectroscopic studies at controlled excitation density and temperature on Mn:CsPbCl3 nanocrystals. Our results indicate a two-step process involving exciton localization in a shallow metastable state that mediates the thermally-assisted sensitization of the Mn2+-emission, which is completely quenched for T<200K. At T≤60K, however, such emission surprisingly reappears, suggesting direct energy-transfer from band-edge states. Electron spin resonance supports this picture revealing the signatures of conformational rearrangements below 70K, possibly removing the potential barrier for sensitization. Our results demystify anomalous behaviors of the exciton-to-Mn2+ energy-transfer mechanism and highlight the role of shallow defects in the photophysics of doped perovskite nanostructures.
关键词： Halide perovskite nanocrystals,energy-transfer,spectroscopic studies,Mn2+ dopants,shallow states
更新于2025-09-09 09:28:46
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A Computational Study on the Variation of Bandgap Due to Native Defects in Non-Stoichiometric NiO and Pd, Pt Doping in Stoichiometric NiO
摘要： This paper presents a computational study of non-stoichiometric nickel oxide in a 64-cell NiO system to model and validate localized heating effects due to nanosecond laser irradiation. Variation in the Bandgap of NiO is studied as a function of varying concentrations of native defects, ranging from 0 to 25%. It is observed that there is a slight increase in the bandgap from 3.80 eV for stoichiometric NiO to 3.86 eV for Ni-rich NiO and to 3.95 eV for O-rich NiO. It is hence deduced that the experimental laser irradiation leads to simultaneous reduction of Ni2+ ions and the oxidation of NiO as the number of laser pulses increase. As well, a detailed study on the effects of doping nickel family elements, i.e., palladium (Pd) and platinum (Pt), in stoichiometric NiO is presented. A bandgap decrease from 3.8 eV for pure NiO to 2.5 eV for Pd-doping and 2.0 eV for Pt-doping for varying doping concentrations ranging from 0–25% Pd, Pt, respectively, is observed.
关键词： dopants,platinum,palladium,nickel oxide,bandgap
更新于2025-09-04 15:30:14