Band Gap Of Compound Research Articles

Growth and characterization of Sb2(SxSe1-x)3 thin films prepared by chemical-molecular beam deposition for solar cell applications

Antimony sulfide selenide, Sb2(SxSe1-x)3 (x = 0–1), is a tunable bandgap compound that combines the advantages of antimony sulfide (Sb2S3) and antimony selenide (Sb2Se3). This material shows great potential as a light-absorbing material for low-cost, low-toxicity, and highly stable thin-film solar cells. In this study, Sb2(SxSe1-x)3 thin films were deposited by chemical-molecular beam deposition on soda-lime glass substrates using antimony (Sb), selenium (Se), and sulfur (S) precursors at a substrate temperature of 420 °C. By independently controlling the source temperatures of Sb, Se, and S, Sb2(SxSe1-x)3 thin films with varying component ratios were obtained. Scanning electron microscopy revealed significant changes in the surface morphology of the films depending on the elemental ratio of [S]/([S]+[Se]). Crystallites shaped like cylindrical microrods with d = 0.5–2 µm diameter and l = 3–5 µm length were grown at a certain angle on the substrate. X-ray diffraction patterns showed peaks corresponding to the orthorhombic structures of Sb2Se3, Sb2S3 and their ternary compounds Sb2(SxSe1-x)3. The optical characterization revealed a high absorption coefficient of 105 cm−1 in the visible and near-infrared light regions. The band gap of the compounds changed almost linearly from 1.2 eV to 1.36 eV with a change in the ratio of elements [S]/([S]+[Se]) from 0.03 to 0.08.

Lead-free semiconductor materials with high phase transition temperature: [1-Methylimidazole][SbBr4]

Semiconductor with structure phase change is a special multi-functional material, which plays an important role in the field of Solar Energy, information computing, sensor technology, artificial intelligence, etc. In this paper, the organic–inorganic lead-free semiconductor phase change material [1-Methylimidazole][SbBr4] (1) was successfully constructed. The IR, TGA, DSC, VT-PXRD, solid-state UV–vis spectroscopy and temperature dependence of dielectric constant were characterized and analysed. Single crystal X-ray diffraction shows that at 298 K, the space group is P21/c, the point group 2/m; an endothermic and exothermic peak appeared near 386 K and 367 K in the DSC heating–cooling cycles. Near the corresponding phase transition temperature point, compound 1 exhibits a significant reversible change in the dielectric platform. Interestingly, the band gap of compound 1 is about 2.53 eV. The existence of such interesting physical properties is closely related to the interaction between cations and anions in the molecule and the connection of internal hydrogen bonds. By constructing organic–inorganic hybrid semiconductor materials, we hope to obtain semiconductor materials with phase transition properties and actively explore and provide some ideas and support for the application of new high-tech materials.

III-V material-based junction-free L-shaped gate normal line tunneling FET for improved performance

In this paper, we introduce a novel III–V compound material-based junction-free (JF) L-shaped gate normal line tunneling field-effect transistor (III–V JF L GNLTFET) for improved output performance at 0.5 V operation. The key design metric, i.e. JF or junctionless design, in our device eliminates issues like random dopant fluctuations (RDF) and high thermal budgets and streamlines the fabrication. The implementation of III–V compound material, i.e. low bandgap compound GaSb, in the source region, combined with the larger area gate normal line tunneling, improves the ON current for our proposed III–V JF L GNLTFET device. Additionally, the utilization of large bandgap GaAs compounds on the drain and channel sides eliminates ambipolarity and further enhances the performance of our proposed device. Meaning that the proposed device simultaneously improves the ON current and suppresses the ambipolarity. Our proposed III–V JF L GNLTFET exhibits enhanced output performance with an ON current of 23.2 μA μm−1 and a minimum and average subthreshold swing of 3.7 mV dec−1 and 15.82 mV dec−1 respectively. Furthermore, the proposed III–V JF L GNLTFET also gives superior RF/analog performance with transconductance (168.65 μS), cut-off frequency (33.52 GHz), gain-bandwidth product (5.11 GHz), and transconductance-frequency product (243.7 GHz).

First-principles calculations to investigate pressure effect on structural, mechanical, electronic and thermodynamic properties of NADFP·DMF

NADFP·DMF has good detonation performance, mechanical sensitivity and high thermal decomposition temperature. Current studies on NADFP·DMF have been carried out at ambient temperature and pressure, and its properties under pressure have yet to be analysed in depth. By using the generalized gradient approximation (GGA) plane-wave norm conserving pseudopotential method based on the framework of density functional theory, the structural, mechanical, electronic and thermodynamic properties of the monoclinic crystal system NADFP·DMF under 0–20 GPa are calculated. The calculations show that the lattice parameters decrease with increasing pressure. The structure is mechanically stable and ductile within 0–20 GPa. We analyzed electronic properties, including band structure and density of states. NADFP·DMF is a direct band gap compound only at 15 GPa, and the band gap decreases with increasing pressure, resulting in an increase in sensitivity. In addition, the thermodynamic properties of NADFP·DMF are investigated, including enthalpy, temperature*entropy, Gibbs free energy, Debye temperature and heat capacity.

Novel III-V inverted T-channel TFET with dual-gate impact on line tunneling, with and without negative capacitance

We introduce two novel III-V inverted T-channel vertical line tunnel field-effect transistor (TFET) configurations, leveraging staggered bandgap compound materials. Design D-1 operate s without negative capacitance, while Design D-2 incorporates negative capacitance. Both designs employ area-enhanced gate normal line tunneling with dual-gate impact, utilizing InGaAs and GaAsSb materials to effectively reduce the overall bandgap. The double-area line tunneling, facilitated by the double gate, significantly enhances performance. D-1 exhibits notable improvements, with an ION value reaching 596.55 μA/μm, an ION/IOFF ratio of 2.5 × 108, a minimum subthreshold swing (SS) of 9.75 mV/dec, and an average subthreshold swing (AVSS) of 31.93 mV/dec. Building upon these achievements, D-2 takes a step further by implementing NC through a ferroelectric layer gate stack, significantly increasing the line tunneling rate symmetrically on the left and right channels beneath both gates. This marks the first proposal of double gate area-enhanced line tunneling with negative capacitance in this paper. D-2 demonstrates remarkable performance for future low-power applications.

Two new selenidostannates TM-Sn-Se (TM = transition metal) photoelectrocatalytic materials

In recent decades, chalcogenides have appealed extensive attention due to potential applications in photoelectric materials. Two selenidostannates, [Fe1.11Zn0.89(en)3]2Sn2Se6 (1, en = ethylenediamine) and [Co1.24Zn0.76(en)3]2Sn2Se6 (2) were synthesized by solvothermal method with ethylenediamine and ethylene glycol as the solvents, both consisting of complexes in which the two different transition metals occupied the same position and [Sn2Se6]4− anions. Transition metal complexes (TMCs) can combine photoelectric properties with inorganic skeletons to extend their compound properties. Therefore, we investigated the photocurrent response of both compounds and found higher transient photocurrent densities. The band gaps of compounds 1 and 2 were calculated to be 2.31 eV and 2.17 eV, respectively, indicating that two compounds have potential semiconductor properties. In addition, we also studied the photodegradation efficiency of compounds 1 and 2 and found that the degradation efficiency of two compounds could be achieved 84.5 % and 55.9 %, which indicated that the compounds have excellent photocatalytic properties. The field of photoelectrocatalytic research on selenidostannates is broadened.

Rashba Spin Splitting Limiting the Application of 2D Halide Perovskites for UV-Emitting Devices.

Layered lead halide perovskites have attracted much attention as promising materials for a new generation of optoelectronic devices. To make progress in applications, a full understanding of the basic properties is essential. Here, we study 2D-layered (BA)2PbX4 by using different halide anions (X = I, Br, and Cl) along with quantum confinement. The obtained cell parameter evolution, supported by experimental measurements and theoretical calculations, indicates strong lattice distortions of the metal halide octahedra, breaking the local inversion symmetry in (BA)2PbCl4, which strongly correlates with a pronounced Rashba spin-splitting effect. Optical measurements reveal strong photoluminescence quenching and a drastic reduction in the PL quantum yield in this larger band gap compound. We suggest that these optical results are closely related to the appearance of the Rashba effect due to the existence of a local electric dipole. The results obtained in ab initio calculations showed that the (BA)2PbCl4 possesses electrical polarization of 0.13 μC/cm2 and spin-splitting energy of about 40 meV. Our work establishes that local octahedra distortions induce Rashba spin splitting, which explains why obtaining UV-emitting materials with high PLQY is a big challenge.

Potassium doping for grain boundary passivation and defect suppression enables highly-efficient kesterite solar cells

The complicated and diverse deep defects, voids, and grain boundary in the CZTSSe absorber are the main reasons for carrier recombination and efficiency degradation. The further improvement of the open-circuit voltage and fill factor so as to increase the efficiency of CZTSSe device is urgent. In this work, we obtained K-doped CZTSSe absorber by a simple solution method. The medium-sized K atoms, which combine the advantages of light and heavy alkali metals, are able to enter the grain interior as well as segregate at grain boundary. The K-Se liquid phase can improve the absorber crystallinity. We find that the accumulation of the wide bandgap compound K2Sn2S5 at grain boundary can increase the contact potential difference of grain boundary, form more effective hole barriers, and enhance the charge separation ability. At the same time, K doping passivates the interface as well as bulk defects and suppresses the non-radiative recombination. The improved crystallinity, enhanced charge transport capability and reduced defect density due to K doping result in a significant enhancement of the carrier lifetime, leading to 13.04 % device efficiency. This study provides a new idea for simultaneous realization of grain boundary passivation and defect suppression in inorganic kesterite solar cells.

Antimony Bromide Organic-Inorganic Hybrid Compound with a Long-Chain Diamine Showing Switchable Phase Transition and Second-Harmonic Generation Properties.

Organic-inorganic hybrid metal halides have attracted significant attention in recent years due to their excellent optoelectronic properties and potential applications in solar cells. Herein, the organic-inorganic hybrid molecule [N,N-dimethyl-1,3-propanediamine]SbBr5 (1) was synthesized by reacting a long-chain organic diamine N,N-dimethyl-1,3-propanediamine with SbBr3 as a metal halide precursor in HBr aqueous solution. Compound 1 possesses a one-dimensional chainlike structure with the second-harmonic generation switch and two continuous phase transitions above room temperature. The band gap of compound 1 is about 2.62 eV, exhibiting a semiconductive property, which may have important implications for the development of new optoelectronic devices.

Structural, electronic, and optical properties of three types Ca3N2 from first-principles study.

To find the potential value of Ca3N2 in the field of optoelectronics, the physical properties of Ca3N2 will be analyzed. It can be concluded from the electronic properties that the Ca-N bonds of α-Ca3N2 are more stable than those of δ-Ca3N2 and ε-Ca3N2. The dielectric function, reflectivity function, and absorption function of three types of Ca3N2 were accurately calculated, and it was concluded that α-Ca3N2, δ-Ca3N2, and ε-Ca3N2 have greater transmittance for visible light and exhibit optical transparency in the near-infrared frequency domain. Combined with the high hardness, strong bonding, high melting point, and wear resistance of Ca3N2, Ca3N2 can be used as a new generation of window heat-resistant materials. The α-Ca3N2, δ-Ca3N2, and ε-Ca3N2 are indirect, direct, and indirect narrow bandgap compounds, respectively, that is, δ-Ca3N2 is more suitable for luminescent materials than α-Ca3N2 and ε-Ca3N2. α-Ca3N2 and δ-Ca3N2 have high reflective properties in the ultraviolet region and can be used as UV protective coatings. All three Ca3N2 materials can be used industrially to synthesize photovoltaic devices that operate in the ultraviolet region. Based on the first-principles of density functional theory calculations, the structures, electronic properties, and optical properties of α-Ca3N2, δ-Ca3N2, and ε-Ca3N2 were calculated. The calculation results show that although the α-Ca3N2, δ-Ca3N2, and ε-Ca3N2 have similar electronic structures, some phases have better properties in some aspects.

Band gap predictions of double perovskite oxides using machine learning

The compositional and structural variety inherent to oxide perovskites spawn wide-ranging applications. In perovskites, the band gap Eg, a key material parameter for these applications, can be optimally controlled by varying the composition. Here, we implement a hierarchical screening process in which two cross-validated and predictive machine learning models for band gap classification and regression, trained using exhaustive datasets that span 68 elements of the periodic table, are applied sequentially. The classification model separates wide band gap materials, with Eg ≥ 0.5 eV, from materials which have zero or relatively small band gaps, namely Eg < 0.5 eV, and the second regression model quantitatively predicts the gap value of the wide band gap compounds. The study down-selects 13,589 cubic oxide perovskite compositions that are predicted to be experimentally formable, thermodynamically stable, and have a wide band gap. Of these, a subset of 310 compounds, which are predicted to be stable and formable with a confidence greater than 90%, are identified for further investigation. Our models are methodically analyzed via performance metrics and inter-dependence of model features to gain physical insight into the band gap prediction problem. Design maps to identify the variation of band gap with substitution of different elements are also presented.

Y(HSeO3)(SeO3)(H2O)·(H2O) and Y2(SeO3)2(SeO4)(H2O)2·(H2O)0.75: Two yttrium selenites with a short UV cut-off edge explored from pure selenite compounds

Two UV inorganic yttrium selenite optical materials, namely, Y(HSeO3)(SeO3)(H2O)·(H2O) (1) and Y2(SeO3)2(SeO4)(H2O)2·(H2O)0.75 (2), have been synthesized successfully by hydrothermal reactions. Of these, Y2(SeO3)2(SeO4)(H2O)2·(H2O)0.75 (2) is a new mixed valent selenium oxide containing Se(IV) and Se(VI) cations simultaneously. Y(HSeO3)(SeO3)(H2O)·(H2O) (1) shows a 3D structure composed of 2D yttrium selenite layers linked by O−H···O bonds. Y2(SeO3)2(SeO4)(H2O)2·(H2O)0.75 (2) exhibits a 3D structure composed of 2D yttrium selenite layers connected by SeO4 tetrahedron. Y(HSeO3)(SeO3)(H2O)·(H2O) (1) crystallized in a chiral space group P212121 and could display a moderate SHG intensity about 0.7 times of the commercial KH2PO4 (KDP). Its powder laser damage threshold quantity was estimated to be 120.2 MW/cm2, which is about 46.2 times that of AGS (2.6 MW/cm2). UV–vis–NIR spectra reflectance spectra showed that these solids are wide band gap compounds with Eg of 5.5 and 5.1 eV respectively. Theoretical calculations disclosed that Y(HSeO3)(SeO3)(H2O)·(H2O) (1) is an indirect band gap structures and its bandgaps is determined by O and Se atoms.

Narrow Band Gap Compounds with β‐Pyrochlore Structure in the A2O‐V2O5‐2TeO3 (A=Rb, Cs) System

AbstractTwo new isostructural compounds with composition of Rb+V3+0.125V5+0.625Te6+1.25O6 and Cs+V3+0.125V5+0.625Te6+1.25O6 have been synthesized by solid‐state reaction. The crystal structure has been determined by X‐ray diffraction analysis using Rietveld refinement. Both compounds possess β‐pyrochlore structure‐type with cubic space group Fd‐3 m (Z=8); the unit cell parameters: a=10.04120(27) Å for RbV0.75Te1.25O6 Å and a=10.09119(23) Å for CsV0.75Te1.25O6. The oxidation states of vanadium and tellurium have been confirmed by X‐ray photoelectron spectroscopy. The compounds contain vanadium in mixed valence state (3+ and 5+). The compounds possess the unusual narrow band gap for oxide compounds – in the infrared (IR) range (∼0.6 eV). The schematic electronic structure of the compounds has been estimated using XPS, UPS and electronic conductivity data; however, the shifts of the top of the valence edge and the bottom of the conduction band in the water conditions have been calculated using theoretical approximation. The thermal behavior of obtained compounds has been studied by differential thermal analysis. RbV0.75Te1.25O6 and CsV0.75Te1.25O6 melts at low temperatures (∼500 °C) with decomposition and weight loss. The RbV0.75Te1.25O6 powder decomposes to amorphous phase, whereas CsV0.75Te1.25O6 transform into new β‐pyrochlore compound with another composition.

Synthesis, structure and characterization of Cd2TeO3Cl2 with unprecedented [Cd2O6Cl4] octahedral dimers.

A new mixed anionic compound Cd2TeO3Cl2 with unprecedented [Cd2O6Cl4] octahedral dimers has been synthesized, and millimeter-scale single crystals of Cd2TeO3Cl2 have been grown by the vertical Bridgman method with CdCl2 as the flux. Cd2TeO3Cl2 crystallizes in the centrosymmetric P1̄ (no. 2) space group, and shows a mixed cationic layer structure constituted by distorted [TeO3] motifs, mixed anionic [Cd2O6Cl4] chains, and [Cd2O6Cl4] octahedral dimers. Experimental and theoretical results show that Cd2TeO3Cl2 is a direct band gap compound with an experimental band gap of ∼4.25 eV. Meanwhile, the compound has good optical transmittance in the 3-5 μm atmospheric window. The results indicate that Cd2TeO3Cl2 could be used as a promising mid-IR window material, and could enrich the chemical and structural diversity of oxides.

Microwave synthesized erbium vanadate nano-photocatalyst: Application for enhanced degradation of contaminated water

The subject of treatment of real or synthetic industrial effluents and photocatalysts has concerned a lot of consideration from scientists. Among the diverse metal oxide photocatalytic materials, the narrow bandgap compounds are of superior significance owing to appropriate efficiency in the optical application. In this work, we produced pristine ErVO4 through the microwave-assisted synthesis method. Diverse solvents and different power intensities have been employed in this preparation for size controlling and shape engineering, such as Ethylene glycol (EG), Propylene glycol (PG), and Polyethylene glycol (PEG-400) and power of 900, 750 and 600 W. XRD, FT-IR, and EDS analysis have been utilized to demonstrate the phase purity, and FE-SEM and TEM were employed to discover the shape of resultant ErVO4. The several attributes of the samples, such as the surface area, magnetic and optical features, were inquired by BET, VSM and DRS techniques, correspondingly. Microwave power of 900 W and Ethylene glycol solvent was selected as an optimal condition owing to the creation of uniform nanosized particles. So nanostructured ErVO4 was operated as a catalyst for the decolorization of colored pollutants (Erythrosine (ER), Methyl Orange (MO), and methylene blue (MB)). According to the discoveries, the MB with higher photocatalytic efficiency was compared in different dye concentrations and catalyst loading experiments to attain ideal performance.

Analysis of a novel method of alkalis treatment: Effect on energy band optimization and carrier recombination at the grain boundary

Alkali metal post-deposition treatment (PDT) is a key factor to approach high efficiency in Cu(In, Ga)Se 2 (CIGS) solar cells. In addition to single alkali element treatment, co-doping of light and heavy alkali elements is also applied to the preparation of CIGS absorber for higher efficiency. In this work, the details of different methods of alkali-treatments are revealed by combining several microstructural and compositional analysis methods, especially for the NaF-PDT/CsF-PDT process which introduces extra Na before Cs into the absorber. The ion exchange of Na and Cs in the grain boundaries (GB) of the absorber is analyzed in detail, which reveals alkali-treatment restrains the formation of large bandgap compounds at GB. Extensive material analysis shows that NaF/CsF-PDT can not only tailor the surface nanoscale morphology of CIGS films but also optimize the band structure at GB to reduce carrier recombination. Such modification gains the improvement of the highest power conversion efficiency (PCE) from 15.2% to 17.4% and average PCE from 14.3% to 16.5% (without antireflective coating) after NaF/CsF-PDT. According to the analysis of data, we propose a model of energy band at GB, which explains the reason why NaF/CsF-PDT shows a better effect on CIGS devices than CsF-PDT. These results could serve as a basis for the further understanding of the effects of alkali-PDT on CIGS film and help to achieve even higher efficiency. • Effects of alkali elements Na and Cs on CIGS solar cells are investigated by a series of characterization tools. • NaF/CsF-PDT can tailor the surface nanoscale morphology and optimize the band structure at CIGS films. • An energy band model of GBs is proposed to explain the effect of alkali metal co-doping. • The PCE improved from 15.2% to 17.4% after NaF/CsF-PDT.

Structural, electronic, optical and mechanical properties of oxide-based perovskite ABO3 (A = Cu, Nd and B = Sn, Sc): A DFT study

The structural, electronic, optical and mechanical properties for oxide-based cubic perovskites ABO3 (A ​= ​Nd, Cu and B= Sc, Sn) were investigated employing density functional theory (DFT) within the CASTEP (Cambridge Serial Total Energy Package) code, based on ultra-soft pseudo-potential (USP) plane wave and Perdew Burke Ernzerhof (PBE) exchange-correlation functional of Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA). The structural results showed that all compounds are stable. The computed elastic constants also meet the requirements of mechanical stability, hardness, ductile/brittle and bonding nature of materials. All the compounds have anisotropic nature. The electronic band structure calculations show that CuScO3 and CuSnO3 compounds have indirect band gap nature. NdScO3 compound has a direct band gap and NdSnO3 compounds show metallic behavior. All the compounds were identified as semiconductors, except NdSnO3 compounds. The band gap values were in the best agreement with the information that is already available. Partial density of states (PDOS) and total density of states (TDOS) were employed to measure the degree of localized electrons in different bands. The optical transition in the compounds was computed by fitting the dispersion relation of the imagined component. Optical properties showed that these compounds were excellent absorbers of incident radiation. Therefore, it may be assumed that these compounds could be in employment in optoelectronics to capture the ultraviolet range of solar radiations.

Cs2B4O5(OH)4: A new hydrated borate with a short UV cutoff edge

A new hydrated cesium borate, Cs2B4O5(OH)4 was synthesized successfully in a vacuum system. It crystallizes in the monoclinic space group P21/c with unit cell of dimensions a = 7.6907(6) Å, b = 13.2044(12) Å, c = 9.3636(7) Å, β = 94.211(3) °, V = 948.32(13) Å3, Z = 3. It takes [B4O5(OH)4]2− polyborate anions as the fundamental building blocks (FBB) which are combined through the Cs-O polyhedra to form a three-dimensional (3D) network. The UV–vis-NIR spectrum shows that Cs2B4O5(OH)4 possesses an ultraviolet (UV) cut-off edge below 200 nm which indicates that it may be applied in the UV region. In addition, the relationship between the structure and optical properties of this compound have been studied. The calculated band structures and the density of states indicate that Cs2B4O5(OH)4 is a direct band gap compound with a band gap of 5.14 eV and the moderate birefringence.

Physical Properties of Sr2MWO6 (M=Ca, Mg) for Renewable Energy Applications

Herein, the physical properties of Sr2MWO6 (M = Ca, Mg) double perovskite oxides are evaluated using an ab initio technique with full‐potential linearized augmented plane wave (FP‐LAPW) method. It is revealed that Sr2CaWO6 and Sr2MgWO6 are direct bandgap (Eg) compounds with Eg of 4.4 and 4.3 eV, respectively. The stability of Sr2MWO6 (M = Ca, Mg) compounds is in cubic lattices, which is ensured by calculating the tolerance factor (τ) and formation energy (ΔH). The optical features such as dielectric constants (ε1, ε2), optical conductivity σ(ω), refractive index n(ω), absorption coefficient α(ω), extinction coefficient k(ω), and reflectivity R(ω) are computed within the energy span of 0–10 eV. Finally, BoltzTrap code is utilized for the calculations of thermoelectric (TE) properties and the calculated values of figure of merit (ZT) for Sr2CaWO6 and Sr2MgWO6 are 0.7775 and 0.7471, correspondingly. The analysis of optical and TE characteristics indicates that the Sr2MWO6 (M = Ca, Mg) compounds are suitable for ultraviolet photodetectors, solar cells, and TE applications.

Incorporation of Na into Ag2ZnSnSe4 from hybrid functional calculations

In the present study, first-principles calculations are performed to study the structural, elastic, electronic, and optical properties of Ag2ZnSnSe4 (AZTSe) and Ag1.5Na0.5ZnSnSe4 (ANZTSe) for the first time. The dopant formation energy and phonon dispersion ensure the thermodynamic stability of ANZTSe. The tendency of phase separation still exists for ANZTSe. In addition, the mechanical stability of ANZTSe is confirmed. The electronic and optical properties of AZTSe and ANZTSe are analyzed by employing the hybrid functional PBE0. The results show that the substitution of Na for Ag results in the increasing band gap of AZTSe. ANZTSe is a direct bandgap compound with the value of 1.54 eV. It is found that AZTSe and ANZTSe have low carrier effective masses and show good mobility. The visible light absorption capacity of ANZTSe is slightly lower than that of AZTSe. In general, ANZTSe is the potential candidate for solar cells.