High Absorption Coefficient Research Articles

Evaluation of the phonon, optoelectronic, photovoltaic, thermoelectric, photocatalytic and thermodynamic properties of the inorganic perovskite CsPbI2Br using Ab initio calculations

Inorganic CsPbI2Br perovskites, derived from cesium, hold potential for use in solar and optoelectronic devices. This study utilized density functional theory calculations to investigate the structural, phonon, electronic, optical, photovoltaic, thermoelectric, thermodynamic, and photocatalytic properties of CsPbI2Br. The phase stability of our compound is thoroughly researched, and it is confirmed that all are thermodynamically and dynamically stable. Formation energy is employed to confirm thermodynamic stability while phonon dispersion is used to confirm dynamical stability. We have computed the electronic properties of CsPbI2Br, such as PDOS, TDOS, and its band structure. The results indicate that the material is a p-type semiconductor which has a direct gap value of 1.50 eV and 1.92 eV using GGA-PBE and TB-mBJ respectively. Higher absorption coefficient, optical conductivity, reflectivity and other optical properties of the CsPbI2Br compound indicate better absorption in the visible spectrum. This distinguishes this substance as an exceptional candidate for optoelectronic devices. Improved utilization of CsPbI2Br in thermoelectric devices is evident from the power factor PF, Seebeck coefficient, figure of merit, and other thermoelectric properties. CsPbI2Br is advantageous in the solar industry due to its external quantum efficiency, open-circuit voltage of 1.92 V, and short-circuit current of 19.67 mA.cm−2. Additionally, the study examined the compound’s thermodynamic properties and examined how the temperature affected its entropy, free energy, enthalpy and heat capacity. Furthermore, it meets the thermodynamic necessary conditions to initiate the water-splitting reaction; the CsPbI2Br compound demonstrates strong photocatalytic performance. This implies that CsPbI2Br may open up new avenues for thermoelectric and optoelectronic experimentation.

Easily manufacture lightweight EPDM/POE/KB foam with high electromagnetic shielding efficiency and high absorption coefficient through chemical foaming

Utilizing foam-structured composite materials for electromagnetic shielding offers several advantages, including lightweight properties, low filler load, and a high absorption coefficient. However, their application in electromagnetic shielding is often limited by relatively lower mechanical performance. This study employed melt blending and chemical foaming processes to fabricate a lightweight EPDM/POE/KB composite foam with favorable mechanical characteristics, heat resistance, and electromagnetic absorbing performance. Significantly, the foam, with a density of 0.195 g/cm³, demonstrates an absorption-dominated shielding mechanism (absorption coefficient of 0.71) and good electromagnetic shielding performance of 20.57 dB in the X-band. The honeycomb structure formed within the material contributes to the multiple reflections of electromagnetic waves. Additionally, the composite foam exhibits excellent flexibility, with a fracture elongation greater than 150 %, alongside tensile and compressive strengths of 1.46 MPa and 0.92 MPa, respectively, demonstrating satisfactory mechanical performance. Furthermore, the composite foam also possesses good thermal stability. The study provides a low-cost and effective method for preparing lightweight, high-absorption coefficient, and excellent mechanical performance electromagnetic shielding foam.

Halide tuning in derivative organic–inorganic perovskites, MAPb(Br1-xClx)3 (x = 0–1): exploring structural, optical and vibrational characteristics

Organic–inorganic metal halide perovskites (OIMHP’s), particularly CH3NH3PbX3 (X = I, Br, Cl) and their derivatives shows favorable properties for energy harvesting such as high absorption coefficients, adjustable band gaps, and low charge recombination rate. The structure and hence nature of bonding between different atoms of these perovskites is known to affect their properties significantly. Tuning of band gap can be achieved in these systems with the help of compositional variation. These systems are studied extensively in the single halide compositions (MAPbI3, MAPbBr3 and MAPbCl3); while, their derivatives seem to have gained less attention though being important for various applications. So, in this work, halide tuning is achieved in derivative perovskite, MAPb(Br1-xClx)3 (x = 0 to 1) and further studied for structural and optical properties along with vibrational properties using X-ray diffraction (XRD), diffuse reflectance spectroscopy, and Raman spectroscopy techniques, respectively. A decrease in the lattice parameter is observed as the Chlorine content increases in the MAPb(Br1-xClx)3 (x = 0 to 1) perovskite. The substitution of Chlorine with Bromine also results in significant increase in the band gap value. In contrast to previous reports, it was clearly observed that the Urbach energy strongly depends on the composition. For the first time, appearance of two features for torsional mode of methylammonium (MA) is discussed even at room temperature, indicative of disorder. It is observed that although the band gap tuning is achieved with the help of halide mixing (Br and Cl), it is also found to introduce disorder in the intermediate compositions; while, the stability increases toward Chlorine compositions. Interestingly, the information of disorder is found to be contained in both the global as well as local measurements which opens up new pathways for studying these materials. This study will lay down a pathway for better understanding of key properties of these hybrid mix halide perovskites which are promising material for futuristic energy applications.

First-principles study on the electronic structure and photocatalytic properties of novel two-dimensional Janus CrXCN4 (X = Si, Ge)

Abundant studies demonstrate the significant role of Janus-structured two dimensional semiconductors as photocatalytic materials, highlighting their substantial advantages and importance in photocatalysis. In this work, CrXCN4 (X = Si, Ge) Janus monolayers were constructed based on CrC2N4, and the thermal stability, thermodynamic stability, mechanical stability, electronic properties, and optical properties of the monolayers were systematically investigated. Furthermore, an investigation was conducted to examine the impact of biaxial strain on their electronic and light absorption properties. The findings reveal that both monolayers exhibit direct band gap characteristics, with high absorption coefficients for visible light owing to their appropriate band gaps (1.44 eV for CrSiCN4 and 1.15 eV for CrGeCN4, respectively). At compressive strains exceeding 3%, the CrSiCN4 monolayer demonstrates an optimal band edge position, suggesting its potential as a photocatalyst for overall water splitting. Furthermore, as the compressive strain increases, the absorption spectra have blue-shifted and the absorption coefficient becomes higher, exceeding 2 × 105 cm−1 under a −3% compressive strain. Our study highlights the potential applications of CrXCN4 monolayers in the field of optoelectronic device, particularly emphasizing the promising candidacy of CrSiCN4 as an efficient photocatalyst.

First-principles calculation to investigate electronic, optical, and mechanical properties of halide perovskite LiABr3 (A = Ca, Sr, and Ba) for optoelectronic technologies

This study thoroughly explored the physical properties of LiABr3 (A = Ca, Sr, and Ba) cubic perovskites using first-principles density-functional theory. The computed lattice parameters with the GGA-PBE and GGA-PBEsol functionals agree well with previous investigations. The computed negative formation energies (ΔEf) ensure the thermodynamic stability of all three compounds. The investigations reveal that LiCaBr3, LiSrBr3, and LiBaBr3 have bandgaps of 3.02 eV, 2.95 eV, and 2.87 eV, respectively. Elastic constants were computed to gain insights into the mechanical properties of these materials. Positive elastic constant values (Cij) for all three compounds indicate their mechanical stability. Poisson's ratio, Pugh's ratio, and positive Cauchy pressure values suggest that all three compounds exhibit ductile behavior. For the structures LiCaBr3, LiSrBr3, and LiBaBr3, the investigated values of dielectric constant ε1(0) are 3.1, 3.0, and 2.9, respectively. The materials' high absorption coefficient in the ultraviolet spectrum indicates suitability for implementation in UV optoelectronic devices.

Ab Initio Study of the Graphyne-like γ-SiC Nanoflake for Toxic Gas-Sensing Applications.

This study focuses on the geometrical, electronic, and optical properties of the γ-graphyne-like novel γ-SiC nanoflake of the γ-silicon carbide (SiC) monolayer using density functional theory calculations. γ-SiC was revealed to be a stable semiconducting nanoflake confirmed by a negative cohesive energy, real vibrational frequencies, and a 1.749 eV energy gap. The adsorption of COCl2, HCN, PH3, AsH3, CNCl, and C2N2 toxic gases on the γ-SiC nanoflake is also studied, which revealed an attractive gas-nanoflake interaction with the adsorption energy ranging from -0.21 to -0.38 eV. The adsorption results in a significant charge transfer between gas-adsorbent complexes. A significant variation in the energy gap and electrical conductivity was observed due to gas adsorption. γ-SiC showed maximum sensitivity at room temperature for CNCl gas. The entire process of adsorption is exothermic and thermodynamically stable. γ-SiC showed a high absorption coefficient over 104 orders with a significant variation in the absorption peak intensity and blue peak shifting. According to the quantum theory and reduced density gradient analysis, all of the gases are physisorbed on the γ-SiC nanoflake due to van der Waals interactions. The obtained results signify the usability of γ-SiC as a potential toxic gas sensor.

Study of defect density of copper vacancies in chalcogenide CuSbS2, CuSbSe2, CuBiS2, and CuBiSe2 heterojunction thin-film solar cells.

In the past decade, a new family of ternary chalcogenide absorber (TCA) materials MIMIIX2 (where MI = Cu, Ag, Pb; MII = Sb, Bi, In; and X = S, Se, Te) have been studied. The copper family of ternary chalcogenide CuSbS2 CuSbSe2 CuBiS2, and CuBiSe2 is an amazing absorber material for thin-film solar cells because of their suitable band gap, high absorption coefficient and inexpensive, nontoxic, environment friendly and sustainable nature. In the presented work, first time simulated defect density of copper vacancies in CuSbS2 (CAS), CuSbSe2 (CASe), CuBiS2 (CBS) and CuBiSe2 (CBSe) has based heterojunction thin-film solar cells (HJTFSCs) with buffer CdS, intrinsic i-ZnO, window ZnO: Al and back contact Mo and set the cell scheming ZnO: Al/i-ZnO/n-CdS/p-TCA/Mo using SCAPS 1D. Major focus of this paper is on the influence of copper vacancies defect density that impact on the performance of ternary chalcogenide with various parameters of solar cells, i.e. short-circuit current density (Jsc), open-circuit voltage (Voc), form factor (FF) and efficiency (η). The cell parameter set at constant temperature 300K, thickness 2.5μm, carrier density 5 × 1016cm-3, front internal transmission coefficient 1 and illumination intensity 100 mW/cm2 with AM1.5 sun light. This study clarifies the potential benefits to utilizing of ternary chalcogenide compounds as absorber material for solar cell fabrication.

Tuning the essential physical properties of KTaO3 through sulfur, selenium doping, and oxygen vacancy: A first principle investigation

The objective of this work is to use density functional theory (DFT) analysis to explain the effects of sulfur (S), selenium (Se), and oxygen vacancies on the mechanical, electrical, optical, dynamical, and thermoelectric properties of KTaO3. Our investigation has uncovered important modifications to KTaO3 many characteristics, most notably to its band gap values. Crucially, every chemical that was studied showed evidence of both dynamical and mechanical stability. These compounds are also good prospects for a variety of optoelectronic applications due to their promising optical properties, which include strong optical conductivity throughout the visible spectrum, low reflection, and high absorption coefficients. Our thorough analysis has shown the remarkable electrical, optical, and mechanical characteristics, including high absorptivity, low reflectivity, hardness, ductility, and semiconducting behavior. It has also highlighted the stability of all computed phases. The optical characteristics and adjusted band gap of KTaO3 indicate that it has substantial potential for use in solar cells, providing avenues for improving the efficiency of solar energy conversion. In addition, the exceptional heat conductivity of KTaO3 offers exciting opportunities for its use as a heat sink material.

Elemental Composition of the Leaves of the Hanging Birch (<i>Betula pendula</i> Roth) in the Area of the Transbaikalia Gold Deposit

The influence of gold mining on the concentration of chemical elements in Betula pendula Roth leaves was studied. The intensity of absorption by the plant of a number of chemical elements, the possibility of using birch as a medicinal and forage plant, as well as for monitoring habitat changes were investigated. The study was conducted in plant communities located at production facilities and natural habitats in the area of the Baley gold deposit: tailings dumps of gold recovery factories (ZIF-1 and ZIF-2), a drainage landfill, a dump of the SredneGolgotai gold deposit, a tailings dump after processing monocytes, as well as in natural plant communities located in the vicinity of Baley at 13 trial sites in 2008, 2008 and 2021. The concentrations of elements in the leaves were arranged in descending order in the following sequence: Ca Mg P Mn Fe Zn Na Ba B Cr Ni As Cu Mo Sb Pb Co Li V Cd Bi Se Be. With respect to the clark of terrestrial plants, the concentrations of the elements were in the following order: Cr As Sb Li Ni Ba Fe Mo Bi Co Zn Mg Clark Mn P Ca Cu B Pb Se Cd V Be Na. The absorption of As at production facilities exceeded the norm established for medicinal plant raw materials. The use of branch feed in a number of areas is not allowed due to the high level of Zn, Fe, Sb, Ni, Cr, Co, As, Cd. A relatively high coefficient of biological absorption by birch leaves Zn, Mn, P, Ca, Mg was obtained.

Highly stable two-dimensional Janus Transition Metal Dichalcogenide-Based van der Waals heterostructures for exceptional solar cell performance

The development and utilization of solar energy are extremely important for alleviating energy and environmental problems. Herein, we comprehensively fabricated a series of two-dimensional Janus MXY-based van der Waals heterostructures (M=Mo, W; X, Y=S, Se, Te, and X≠Y) and thoroughly investigated their potential applications in solar cells using first-principles density functional theory. Further analysis identifies 20 heterostructures with power conversion efficiencies (PCEs) exceeding 20 %. Additionally, the impact of spin-orbit coupling (SOC) effects and intrinsic dipole correction on band structures and PCEs is examined. Particularly noteworthy are the WSSe/WSeTe SeSe BB and WSeTe/WSTe TeTe BB' vdWHs, exhibiting superior PCEs of 19.25 % (23.51 %) and 21.53 % (20.49 %) with (without) SOC effects and dipole correction, alongside minimal exciton binding energies (0.36 and 0.32 eV), excellent stability, and high light absorption coefficients (105∼106 cm−1). These outstanding values surpass most reported results. These findings underscore the potential of Janus transition metal dichalcogenide (TMD) vdWHs, particularly WSSe/WSeTe SeSe BB and WSeTe/WSTe TeTe BB' configurations, for advanced solar cell applications, offering valuable theoretical insights for future experimental investigations.

Rational synthesis of core/shell heterostructured quantum dots for improved self-powered photodetection performance enabled by energy band engineering

Colloidal quantum dots (CQDs), especially core-shell QDs, have attracted dramatic interests as emerging materials in optoelectronic devices due to their size tuneable band-gap, high absorption coefficient, facile and low-cost synthesis routing, etc. However, the precise design of core/shell band engineering along with charge carrier transfer efficiency are still challenging, inevitably impacting the performance of optoelectronic devices. Herein, three different types of CdSe/CdS core-shell heterostructured QDs have been obtained via a proposed synthesis strategy of adjusting the core size but fixing the shell thickness. The performance of the core-shell QDs based self-powered photodetectors can be efficiently regulated by the optimization of synthesis strategy with the design of energy band alignment. Compared to the quasi type-II and the type-I QDs devices, the Ilight/Idark ratio of type-II heterostructure based photodetector is increased by ∼2 and ∼5 orders of magnitude, respectively. The champion device exhibits extraordinary optoelectronic performance in terms of ultrahigh light-to-dark current ratio of 105, photoresponsivity of 10.64 mA/W, at bias of 0 V, respectively. The charge carrier dynamics and transfer mechanisms of the QDs were further investigated, revealing the improved carrier separation and transportation efficiency induced by a strong build-in electric field in type-II CdSe/CdS core-shell heterostructure. This work provides a new strategy for the next-generation self-powered QDs optoelectronics enabled by the proposed synthesis approach along with the design of energy band alignment.

Novel dual absorber configuration for eco-friendly perovskite solar cells: design, numerical investigations and performance of ITO-C60-MASnI3-RbGeI3-Cu2O-Au

Perovskite solar cells (PSCs) are increasingly being used as the foundation of the worldwide photovoltaic (PV) industry because of their cost-effective production and durable stability. Perovskite materials, both organic and inorganic, possess distinct optical, mechanical, and electrical properties, such as a high absorption coefficient, a customizable band gap, and a synthesis method based on solutions. This study employed numerical investigations to devise and propose innovative solar cell configurations utilizing the SCAPS-1D simulator. This research presents a Perovskite solar cell design comprising an ITO-C60-MASnI3-RbGeI3-Cu2O-Au solar cell configuration. The unique arrangement of this setup incorporates the use of Indium Tin-oxide (ITO) as the upper contact layer, which is directly exposed to light. The electron transport layer (ETL) is composed of a 0.030 μm thick layer of C60, while the light-harvesting/absorber layers are made up of MASnI3 and RbGeI3, each with a thickness of 0.4 µm. A layer of Cu2O with a thickness of 0.12 μm is employed as the hole transport layer (HTL), whereas the back-contact layer consists of Au. A comparison research was conducted to examine the optimal device configuration. Comprehensive studies are performed to assess the effects of different variables on optimized device performance and power conversion efficiency (PCE). These factors include interface defect densities, thicknesses of different structural layers, band gaps, series and shunt resistance, and operational temperature. The current density (Jsc) is calculated as 32.7 mA/cm2 at an open circuit voltage (Voc) of 0.914 V. Additionally, we observed a power conservation efficiency (PCE) of 20.19 % and an improved fill factor (FF) value of 65.49 %. The ongoing investigations are likely to be valuable for the development and production of cost-effective and high-performance PSCs.

Recent Excellent Optoelectronic Applications Based on Two-Dimensional WS2 Nanomaterials: A Review.

Tungsten disulfide (WS2) is a promising material with excellent electrical, magnetic, optical, and mechanical properties. It is regarded as a key candidate for the development of optoelectronic devices due to its high carrier mobility, high absorption coefficient, large exciton binding energy, polarized light emission, high surface-to-volume ratio, and tunable band gap. These properties contribute to its excellent photoluminescence and high anisotropy. These characteristics render WS2 an advantageous material for applications in light-emitting devices, memristors, and numerous other devices. This article primarily reviews the most recent advancements in the field of optoelectronic devices based on two-dimensional (2D) nano-WS2. A variety of advanced devices have been considered, including light-emitting diodes (LEDs), sensors, field-effect transistors (FETs), photodetectors, field emission devices, and non-volatile memory. This review provides a guide for improving the application of 2D WS2 through improved methods, such as introducing defects and doping processes. Moreover, it is of great significance for the development of transition-metal oxides in optoelectronic applications.

Effect of substrate temperature and position on properties of Cu3N thin films deposited by reactive radio frequency magnetron sputtering

Copper nitride (Cu3N) thin films were deposited on soda lime glass (SLG) substrates by reactive radio frequency (RF) magnetron sputtering using a pure Cu target in the presence of argon and nitrogen. The structural, optical, and electrical properties of the Cu3N films were investigated systematically on substrate temperature and position, demonstrating that both parameters strongly influence the properties of Cu3N thin films. XRD patterns revealed the formation of the Cu3N phase at all substrate temperatures and positions. The transmittance of the Cu3N thin films was over 80 % in the transparent region and the band gap for Cu3N was determined to 1.7–1.9 eV with a very high absorption coefficient above 104 cm−1. The n-type conductivity was observed in every Cu3N film but the resistivity varied considerably with both substrate temperature and position. The promising physical properties of Cu3N thin films suggest their potential application in optoelectronic devices such as thin film solar cells.

Growth and optimization of spray coated Cu2BaSnS4 thin films for solar photovoltaic application

Quaternary multicomponent Cu2BaSnS4 (CBTS) has emerged as a potential absorber material due to its abundant and nontoxic constituents, high absorption coefficient (10−4 cm−1) and suitable bandgap (1.5–2.0 eV) for the solar photovoltaic application. In this study, polycrystalline CBTS thin layers have been deposited by a typical spray pyrolysis technique on glass substrates using different substrate temperatures (Ts = 200, 250, 300 and 350 °C) followed by annealing in a sulfur-rich atmosphere at 550 °C under an argon flow. The (micro-)structural, compositional, and optical properties of both types of films have been studied. Analysis of x-ray diffractogram (XRD) patterns for all acquired films showed the presence of polycrystalline CBTS alongside various secondary phases, including Cu2SnS3 being predominant. Nonetheless, the XRD of the films deposited at 250 °C and annealed at 550 °C showed only the CBTS phase. Raman spectroscopy confirm the formation of the trigonal phase of CBTS. The presence of Cu, Ba, Sn and S in CBTS thin films was confirmed by X-ray photoelectron spectroscopy and Energy-dispersive X-ray spectroscopy. Scanning electron micrographs show a smooth and dense structure with enhanced crystallinity and improved uniformity. Overall, the physical properties of CBTS thin films were found to be spray deposition temperature dependent. An appropriate optical band gap of 1.6 to 1.8 eV and a compact structure indicate their prospective for solar cell applications.

Photocytotoxic and cellular metabolism studies of curcuminoid-BF2 nanoaggregates in human carcinoma cells

Heavy atom-free photosensitizers represent a paradigm shift in the field of photodynamic therapy (PDT), offering a safer and more versatile alternative to traditional photosensitizers. As research progresses, the development of novel heavy-atom free compounds holds the potential to enhance the effectiveness and broaden the application of PDT, enabling the way for more targeted and less toxic cancer treatments. In this article, we report the application of heavy atom free curcuminoid BF2 (Diethylamine-CUR-BF2) containing acid sensitive amine group. Diethylamine-CUR-BF2 absorbs in deep red region at ∼618 nm and has high molar absorption coefficient. Nanoaggregates of Diethylamine-CUR-BF2 dispersed in aqueous medium showed high singlet oxygen production efficiency. The release kinetics of Diethylamine-CUR-BF2 showed efficient release of photosensitizer in slight acidic medium (at pH=5.0). Further, applications of Diethylamine-CUR-BF2 nanoaggregates in photocytotoxic studies using MCF-7 and A549 cells showed IC50 values 5.15 ± 1.4 μM and 8.05 ± 0.4 μM respectively. Cell death mechanism explored for photocytotoxicity studies utilizing Diethylamine-CUR-BF2 nanoaggregates is found to be apoptosis which is considered as normal programmed cell death pathway. Additionally, NADH FLIM studies revealed that the compound had an impact on cellular metabolism, prompting a shift from OXPHOS to glycolysis.

Ab initio study of Ti-doped C3N nanosheet as COCl2, O3, and HCN gas sensor

In the present study, we designed the pristine C3N and Ti-doped C3N nanosheets to investigate the geometrical, electrical, and optical properties using density functional theory calculation. The negative value of the cohesive energy of both nanosheets indicates the structures are energetically stable. Ti-doping in C3N results in a conductor-to-semiconductor transition with a band gap of 0.15 eV. We studied the adsorption of COCl2, O3, and HCN gas molecules on the designed structures. The adsorption energy for COCl2, O3, and HCN gases significantly increased to −8.63, −9.80, and −5.98 eV respectively after Ti-doping. A significant variation in the band gap of Ti-doped C3N is observed due to gas adsorption. The complex structures show a high absorption coefficient of over 104 cm−1 in the visible range with a significant red/blue shifting of absorption peaks. The study proves the Ti-doped C3N to be a potential candidate for sensing COCl2, O3, and HCN gases.

Optoelectronic, thermoelectric and 3D-Elastic properties of lead-free inorganic perovskites CsInZrX6 (I, Cl and Br) for optoelectronic and thermoelectric applications

Halide perovskite materials have recently gained worldwide attention since they offer a new cost-effective way to generate renewable and green energy. In the current work, the structural, electrical, elastic, optical and thermoelectric properties of new perovskites CsInZrX6 (I, Cl and Br) were explored by density-functional theory (DFT). The results indicated that the computed lattice parameters agree really well with the current experimental and theoretical results. Moreover, the band structure profile strongly suggests that the compounds exhibit a semiconducting nature with a direct band gap. The analysis of their optical properties reveals that the perovskites possess a low reflectivity (below 23%) and a high optical absorption coefficient (106 cm−1). This is also supported by the evaluation of their calculated elastic constants and their related parameters in cubic structure which show that these compounds are brittle, mechanically stable and possess covalent bonds. On the other hand, in addition to exhibiting outstanding optoelectronic and mechanical characteristics, CsInZrCl6 also possesses dynamical stability, making it a promising candidate for application in various optoelectronic devices except for solar cells due to its relatively large bandgap. Furthermore, the BoltzTraP software was used to compute the materials’ thermoelectric properties, with the computed values of the figure of merit (ZT) for CsInZrBr6, CsInZrCl6 and CsInZrI6 being 0.76, 0.73 and 0.725, respectively. This is also a strong indication that these materials are potential for thermoelectric applications.

Design and DFT calculations of optoelectronic material based on thiazolobenzimidazole-coupled isatin derivatives

Isatin derivatives were condensedby refluxing ethanol with thiazolobenzimidazole, yielding four linked 2-oxoindolin-3-ylidene)benzo [4,5]imidazo-[2,1-b]thiazol-3(2H)-ones. Thermal evaporation was used to deposit thin films of the produced 2-oxoindolin-3-ylidene)benzo [4,5]imidazo-[2,1-b]thiazol-3(2H)-one derivatives, which underwent thorough analysis employing UV–Vis and NIR spectroscopy. The spectral profiles of these materials were scrutinized with respect to their absorption, dielectricconstants, and dispersion propertiesand compared to previously published data. The current samples were suitable for application in optoelectronic devices, particularly as solar-absorbent materials, due to their high absorption coefficient (α > 105cm−1) at a solar maximum wavelength (λ = 500 nm). Additionally, their band and optical gap energies have been determined as 3.60, 3.56, 2.53, and 3.24 eV. The conclusions drawn from geometry optimization and nonlinear optical (NLO) calculations, performed using density functional theory (DFT) with the Becke, 3-parameter, Lee–Yang–Parr (B3LYP) approach at the 6–311G (d,p) level, further support these findings.

Effect of biaxial strain on the electronic structure and optical properties of two-dimensional Bi2Te2S

In this work, the effects of biaxial strain on the electronic structure and optical properties of monolayer Bi2Te2S are studied by the first-principles methods. The calculated results show that the monolayer Bi2Te2S is an indirect band gap semiconductor with a band gap of 1.0 eV. The absence of imaginary frequency in the phonon spectrum indicates that the structure can exist stably. With the increase of tensile strain, the band gap value decreases approximately quasi-linearly. When 10 % tensile strain is applied, the band gap value is reduced to 0 eV, achieving the transition from an indirect bandgap semiconductor to a direct bandgap semiconductor. With the increase of compressive strain, the band gap value increases first and then decreases, and the band gap value reaches a maximum of 1.28 eV at −4 % strain. Combined with the density of states analysis, the reason for this change in the band structure is that the contribution of Bi 6p, Te 5p and S 3p state electrons to the conduction band and valence band changes under different strains. The effect of strain on the optical properties shows that when different strains are applied, the monolayer Bi2Te2S has a high absorption coefficient in the entire visible region. The single-layer Bi2Te2S material has a smaller refractive index under tensile strain. The static dielectric function value increases with the increase of tensile strain, and the peak value of the dielectric function decreases and moves to the low energy direction. This indicates that the tensile strain will enhance the migration of photogenerated electron-hole pairs, which is beneficial to improving the utilization of light. This work will provide a theoretical reference for the subsequent study of the electronic and optical properties of monolayer Bi2Te2S.