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Correlation between the morphology and the opto-electronic and electrical properties of organometallic halide perovskite (CH<sub>3</sub>NH<sub>3</sub>MH<sub>3</sub>) thin films
摘要： Organometallic halide perovskites are emerging as a promising class of materials for optoelectronic applications. Crystal morphology is important for improving the organic-inorganic lead halide perovskite semiconductor property in optoelectronic, electrical and photovoltaic devices. It is thus important to investigate how the changes in crystal morphology affect the semiconductor behavior. This work presents a study that was carried out to assess the relationship between different deposition methodologies and the opto-electronic and electrical properties of the resultant organometallic halide perovskite thin films. Herein, single step solution deposition method and two step solution deposition methods have been used to deposit perovskite thin films. The structure and morphology of perovskite was controlled by changing concentration, annealing temperatures and dip coating times. From the study, prepared films showed different morphologies as the concentration, annealing temperatures and dip coating times were varied. Optical band gap energies of 2.23 eV, 2.13 eV and 2.09 eV were obtained for samples prepared by single step solution deposition method and 1.57 eV, 1.55 eV and 1.52 eV for two step solution deposition method. The sheet resistance values decreased with an increase in concentration, annealing temperatures and dip coating times. The decrease in optical band gap energy and sheet resistances are excellent properties for high performance photovoltaic devices.
关键词： Perovskite,sheet resistivity,activation energy,band gap,sheet resistance,spectroscopy
更新于2025-11-19 16:56:35
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Solar water splitting over Rh <sub/>0.5</sub> Cr <sub/>1.5</sub> O <sub/>3</sub> -loaded AgTaO <sub/>3</sub> of a valence-band-controlled metal oxide photocatalyst
摘要： Improvement of water splitting performance of AgTaO3 (BG 3.4 eV) of a valence-band-controlled photocatalyst was examined. Survey of cocatalysts revealed that a Rh0.5Cr1.5O3 cocatalyst was much more effective than Cr2O3, RuO2, NiO and Pt for water splitting into H2 and O2 in a stoichiometric amount. The optimum loading amount of the Rh0.5Cr1.5O3 cocatalyst was 0.2 wt%. The apparent quantum yield (AQY) at 340 nm of the optimized Rh0.5Cr1.5O3(0.2 wt%)/AgTaO3 photocatalyst reached to about 40%. Rh0.5Cr1.5O3(0.2 wt%)/AgTaO3 gave a solar to hydrogen conversion efficiency (STH) of 0.13% for photocatalytic water splitting under simulated sunlight irradiation. Bubbles of gasses evolved by the solar water splitting were visually observed under atmospheric pressure at room temperature.
关键词： Rh0.5Cr1.5O3 cocatalyst,valence-band-controlled photocatalyst,solar water splitting,apparent quantum yield,AgTaO3,solar to hydrogen conversion efficiency
更新于2025-11-19 16:51:07
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Alcohol-Guided Growth of Two-Dimensional Narrow-Band Red-Emitting K2TiF6:Mn4+ for White Light-Emitting Diodes
摘要： The use of red phosphors with low light-scattering loss could improve the luminous efficacy and color rendering of white light-emitting diodes (LEDs). Thus, the discovery of such phosphors is highly desired. In this work, high-efficiency two-dimensional red-emitting K2TiF6:Mn4+ (KTFM) were synthesized via an alcohol-assisted coprecipitation route. The synergistic effects of 1-propanol and hydrofluoric acid (HF) on the growth of KTFM microsheets (MSs) were studied through the first-principles calculations, which revealed that 1-propanol promoted the growth of KTFM MSs by preferentially adsorbing on the H-terminated K2TiF6 (001) surface. The photoluminescence quantum efficiency (QE) of Mn4+-activated K2TiF6 MSs was highly related to their size and thickness. The morphology-optimal KTFM MSs presented high internal QE (> 90 %), external QE (> 71%), and thermal quenching temperature (102% at 150 °C relative to that at 25 °C). A prototype phosphor-converted LED with KTFM as the red-emitting component showed an excellent color rendition (Ra = 91, R9 = 79) and high luminous efficacy (LE =156 lm/w).
关键词： light emitting diode,two-dimensional material,Narrow band,K2TiF6:Mn4+,backlight,red emission
更新于2025-11-14 17:04:02
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Time-dependent DFT and experimental study on visible light photocatalysis by metal oxides of Ti, V and Zn after complexing with a conjugated polymer
摘要： Density Functional Theory (DFT) and Time Dependent (TD)-DFT studies predict substantial modifications in optical properties of Transition Metal Oxides (TMOs) of Ti, V and Zn by complexing them with conjugated polymer polythiophene (PTh). The TMO nanostructures were synthesized and their complexes with polymers were fabricated using a chemical oxidative polymerization method. Coating of the TMOs with PTh and the nano-dimensional nature of the samples was confirmed by various morphological investigations such as infrared (IR), X-ray di?ractographs (XRD), High Resolution Transmission Electron Microscopy (HR-TEM) and field emission scanning electron microscopy (FE-SEM) techniques. The prepared samples were found to be a visible light driven photocatalyst. The sensitization of the complexes has been explained in terms of relative ordering of frontier orbitals of PTh and the TMO, and PTh qualified as an e?cient photosensitizer for all three metal oxides on the basis of its electronic characteristics. Since the Highest Occupied Molecular Orbital (HOMO) of PTh lies well between the band gap of all three TMOs, the electron transfer from donor (PTh) to acceptor (TMO) is facilitated. The appreciable red shift in the absorption spectrum and decrease in the optical band gap calculated by Tauc’s plot confirmed substantial reduction in the band gap of the formed complex in comparison to their bare counterparts. The isodensity plots established the PTh–TMO complexes as donor acceptor complexes and intermolecular charge transfer quantified the electron transfer from PTh (donor) to the TMOs (acceptor).
关键词： conjugated polymer,TD-DFT,visible light,metal oxides,DFT,photocatalysis,polythiophene,band gap tuning
更新于2025-11-14 17:04:02
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Temperature sensitive properties of Eu2+/Eu3+ dual-emitting LaAlO3 phosphors
摘要： In this study, Eu2+/Eu3+ coexisting perovskite LaAlO3 phosphors were synthesized by a traditional high-temperature solid-phase reaction method and investigated via X-ray diffraction data, X-ray photoelectron spectroscopy and temperature-dependent photoluminescence spectra. The Eu2+/Eu3+ coexisting LaAlO3 phosphors exhibit excellent optical temperature sensing characteristics and are potential inorganic materials for temperature detection. The measured maximal absolute temperature sensitivity reaches 0.014 K-1, and the corresponding largest relative temperature sensitivity is 1.193% K-1, which are superior to most of previous reports of that. Meanwhile, the monitored signal peaks are well separated, providing a good signal discriminability. The energy level crossover relaxation of Eu2+ and Struck-Fonger crossover process involving O2–-Eu3+ charge transfer band were used to explain the different temperature-dependent responses of Eu2+ and Eu3+. This work may give new ideas for the future research of optical thermometric materials with high sensitivity and high discriminability.
关键词： Fluorescence intensity ratio,Charge transfer band,Thermometry phosphor,LaAlO3
更新于2025-11-14 15:13:28
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Compositional dependence of properties in calcium substituted sodium borophosphate glasses containing $${\hbox {VO}}^{2+}$$ VO 2 + ions
摘要： Synthesis of calcium-substituted sodium borophosphate glasses with compositions xCaO ? (30 ? x)Na2O ? 35B2O3 ? 35P2O5 (x = 0, 2, 5, 7 and 10 mol%, abbreviated as CNVx) containing additional 1.0 mol% of V2O5 following a melt-quench method has been carried out. Different analytical techniques viz. wide angle X-ray diffraction (to con?rm non-crystalline nature), ultraviolet–visible spectroscopy (for optical band gap analysis), infrared absorption spectroscopy (for structural analysis) and differential thermal analysis (to evaluate characteristic temperatures) were employed to characterize the synthesized compositions. The optical band gap is calculated for both indirect allowed and indirect forbidden transitions. The values of the band gap decrease with increasing concentration of CaO (from 5 to 10 mol%) at the cost of Na2O. The cut-off wavelength and Urbach’s energy are determined from the optical absorption spectra and were related to the structural changes occurring in these glasses with an increase in CaO content. The results obtained from Fourier-transform infrared studies con?rm that V2O5 and CaO play the role of network modi?er oxides. Also, the signi?cant shifting in IR bands with an increase in CaO content in the glass matrix suggests the formation of a new boron–oxygen ring. From differential scanning calorimetry measurements it is observed that substitution leads to the increase in natural bond orbitals, high degree cross-linking and thus strengthens the glass network. Glass transition temperature (Tg) is found to increase from 483 to 522?C. Electrical and dielectric properties are analysed using dc conductivity and impedance spectroscopy. Using impedance spectroscopy, different dielectric parameters i.e. dielectric loss (ε(cid:4)), electrical modulus (M ?) and ac conductivity (σac) etc. are evaluated as a function of frequency, temperature and composition. The frequency dependence of impedance exhibits the non-Debye relaxation behaviour and the total conductivity obeys Jonscher’s power law.
关键词： Jonscher’s power law,impedance spectroscopy,Band gap,differential thermal analysis
更新于2025-11-14 14:48:53
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Enhancing light absorption by colloidal metal chalcogenide quantum dots <i>via</i> chalcogenol(ate) surface ligands
摘要： Chemical species at the surface (ligands) of colloidal inorganic semiconductor nanocrystals (QDs) markedly impact the optoelectronic properties of the resulting systems. Here, post-synthesis surface chemistry modification of colloidal metal chalcogenide QDs is demonstrated to induce both broadband absorption enhancement and band gap reduction. A comprehensive library of chalcogenol(ate) ligands is exploited to infer the role of surface chemistry on the QD optical absorption: the ligand chalcogenol(ate) binding group mainly determines the narrowing of the optical band gap, which is attributed to the np occupied orbital contribution to the valence band edge, and mediates the absorption enhancement, which is related to the π-conjugation of the ligand pendant moiety, with further contribution from electron donor substituents. These findings point to a description of colloidal QDs that may conceive ligands as part of the overall QD electronic structure, beyond models derived from analogies with core/shell heterostructures, which consider ligands as mere perturbation to the core properties. The enhanced light absorption achieved via surface chemistry modification may be exploited for QD-based applications in which an efficient light-harvesting initiates charge carrier separation or redox processes.
关键词： colloidal metal chalcogenide quantum dots,light absorption,optoelectronic properties,surface ligands,band gap reduction
更新于2025-10-22 19:40:53
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Tin( <scp>ii</scp> ) thiocyanate Sn(NCS) <sub/>2</sub> – a wide band gap coordination polymer semiconductor with a 2D structure
摘要： Semiconductors based on tin(II) show promising hole-transport characteristics due to the 5s electrons that form the valence band. In this paper, we report the synthesis and comprehensive characterization of tin(II) thiocyanate [Sn(NCS)2] and identify it as a novel transparent coordination polymer semiconductor. The single crystal X-ray analysis reveals covalently-bonded 1D polymeric chains that form a 2D structure through Sn–S tetrel bonds. Density functional theory calculations also confirm the importance of the van der Waals interactions between the 2D sheets. Furthermore, we show that the s character of Sn(II) is maintained at the top of the valence band, resulting in dispersed states with a small hole effective mass. The coordination with NCS ligands also leads to a conduction band which is high in energy, giving rise to a wide band gap and excellent transparency in the visible spectrum. This is the first report on the electronic properties of Sn(NCS)2 which highlights the potential of developing new transparent semiconductors based on thiocyanate coordination polymers.
关键词： hole transport,band gap,tin(II) thiocyanate,transparent,semiconductor,coordination polymer
更新于2025-10-22 19:40:53
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An experimental and theoretical study of the structural ordering of the PTB7 polymer at a mesoscopic scale
摘要： Our extensive study based on optoelectronic and electric measurements (which consisted of: UV-Vis absorption, photoluminescence, surface photovoltage measurement, charge extraction by linearly increasing voltage, and energy-resolved electrochemical impedance spectroscopy) revealed the fundamental role of the thickness of the formation of intra- and interchain interaction in poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) films. We have shown that the final optoelectronic and electronic properties of PTB7 films are governed by the structural ordering development of the transition from nano- to submicroscale. The ordering of polymer chains and competition between the formation of J- and H-aggregates results in a non-trivial dependence of luminescence, exciton diffusion length, transport band gap, and defect concentration. According to a theoretical analysis, the driving forces responsible for the observed phenomena are associated with the thickness threshold dependence of the thin film drying mode which can proceed with or without the polymer skin formation on the surface of forming film.
关键词： low band-gap,thickness dependences,Conjugated polymers
更新于2025-10-22 19:40:53
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A printed dual-band dipole filtenna with flexible frequency ratio and improved band-notched performance
摘要： A printed dual-band dipole filtenna with flexible frequency ratio and improved band-notched performance is proposed. It consists of a driven dipole and three parasitic elements. For the driven dipole with short and long arms, a radiation null is found between two passbands, which achieves a band-notched filtering characteristic. Two parasitic elements are introduced to enhance the passband bandwidth and an additional parasitic element is utilized to improve the band-notched performance. In addition, the characteristics of the proposed design including flexible frequency ratio, independent controllable operating frequency, and controllable band-notched bandwidth have also been demonstrated. A filtenna prototype is fabricated and tested. Measured results show that a fractional bandwidth of 21.1% and 18.1% is obtained in the lower and upper passbands, respectively. The measured efficiency is 84% in the lower band and 74% in the upper band but the efficiency sharply decreases to about 13% within the notched band.
关键词： filtenna,band-notched,dipole antenna,dual-band,frequency ratio
更新于2025-09-23 15:23:52