Optical Absorption Band Research Articles

Synthesis and Optical Properties of Organic-Inorganic Hybrid[(18-Crown-6)K][MoOCl4(H2O)

Crown ether anchored organic-inorganic hybrid halides have been recently reported as interesting luminescent materials in the visible region of electromagnetic spectrum. Is it possible to develop such crown ether anchored hybrid materials for near infrared emission? Motivated by this question, we designed a new hybrid material, namely, [(18-Crown-6)K][MoOCl4(H2O)]. 18-Crown-6 ether bound with K+ form the cationic part [(18-Crown-6)K]+. The K+ of [(18-Crown-6)K]+ electrostatically interacts with Cl- of the anionic part [MoOCl4(H2O)]-, forming the hybrid crystal [(18-Crown-6)K][MoOCl4(H2O)]. It crystallizes in orthorhombic crystal system with Pnma space group. The Mo(V) possesses one d-electron (d1) in C4v point group symmetry in the [MoOCl4(H2O)]- polyhedra. This electronic configuration leads to multiple spin-allowed d-d transitions along with a ligand to metal charge transfer (LMCT) resulting into multiple optical absorption bands in the near UV-visible-near infrared (NIR) region. The lowest energyd-dtransition via 2E to2B2 leads to NIR PL with peak at 952 nm, but with a poor intensity at room temperature.

Roles of defects in perovskite CsPbX3 (X=I, Br, Cl): a first- principles investigation

Inorganic lead halide perovskite CsPbX3 (X=I, Br, Cl) have a promising application in optoelectronic fields due to their excellent photovoltaic properties. The defects, which have a significant impact on the performance of materials, are often introduced during the synthesis process. However, there is still a lack of systematic theoretical investigation of the effects of these defects. In this study, the effects of vacancies and H-atom interstitial point defects on the structural, electronic and optical properties of CsPbX3 are systematically investigated by using first-principles approach based on density-functional theory. The calculated results show that the introduction of different defects have significantly effect on the band gap, effective mass, semiconductor properties, ion migration and optical absorption coefficient of the perovskite materials. It is also found that VCs and VPb defects introduce shallow transition levels that do not negatively impact the optoelectronic properties. However, VX and interstitial H defects generate deep transition levels within the bandgap, which acts as non-radiative recombination centers and reduce the optoelectronic performance of the perovskite material. This study contributes to the understanding of the nature of halide chalcogenides and optimally regulating the performance of optoelectronic devices.

Achieving Tunable Band Structure and Photocarrier Dynamics by Regulating 2D Atomic Layer Stacking Toward High‐Performance Self‐Powered Broadband and Deep‐UV Photodetection

Abstract2D materials with unique layer‐dependent electronic structure can bring precise control to their photocarrier dynamics for optimizing and expanding optoelectronic applications, while the challenge of controlling layer stacking makes the layer dependency law still underexplored in emerging 2D ternary metal chalcogenides. Herein, 2D rhombohedral‐phase ZnIn2S4 (R‐ZIS) with controllable layer thickness is achieved by confined‐growth strategy in high yield, exhibiting continuously tunable direct bandgap (2.39–2.77 eV) with evident upshift of conduction band minimum (CBM) and Fermi level (EF), demonstrated arising from the synergistic effect of reduced interlayer interaction with inevitably increasing Zn defects. Remarkably, the carrier dynamics of R‐ZIS in photoelectrochemical (PEC) device is successfully regulated by adjusted CBM and EF, resulting in continuously tunable optical absorption band, photocarrier separation efficiency, self‐powered capability, and dark current noise. Beneficial from tailored band structure and carrier dynamics, self‐powered PEC‐type photodetector with broadband photoresponse (254–765 nm), is achieved fast response speed (12.3/5.3 ms) and high responsivity (90.29 mA W−1) in multilayer R‐ZIS, while deep‐UV photodetector with ultra‐high specific detectivity (1.62 × 1012 Jones) at 254 nm in monolayer R‐ZIS, exhibiting the record performance in both fields. This work motivates the development of tailored band structure for 2D‐materials‐based optoelectronic devices in strategy and mechanism.

Promising two dimensional XSe2/SnS (X= Pt, Zr, Hf) vdW heterostructures for overall water splitting with higher carrier mobilities

The transition metal dichalcogenides (TMDs) are considered as promising candidates for their striking performance in optoelectronic properties. We have designed the novel heterostructures XSe2/SnS using XSe2 (X = Pt, Zr, Hf) TMDs. The stabilities of structural, mechanical, dynamical, and thermal are calculated by formation energies, elastic constants, phonon dispersions and AIMD simulations respectively. The hybrid functional (HSE06) is used to calculate the electronic band structures and optical absorption. The DFT scheme (BGC based) indicates that XSe2/SnS vdWHs are viable photocatalyst for overall water splitting over a broad spectrum of light. The absorption spectra exhibit that these photocatalysts have absorption started from visible to the UV region of light in the order of 105. XSe2/SnS heterostructures display high carrier mobilities of order 104. The Gibbs free energies exhibit that PtSe2/SnS heterostructure has spontaneous, whereas other heterostructures need some external energies for overall water splitting. Finally, the corrected STH efficiency of PtSe2/SnS, ZrSe2/SnS and HfSe2/SnS vdW heterostructures are 12.54%, 28.15%, 21.03% respectively. This study depicts that XSe2/SnS (X = Pt, Zr, Hf) heterostructures are feasible candidates for overall water splitting over a broad range of light spectrum.

Simulation Study for Nb‐Doped MoS2${\rm MoS}_2$ Layer in CZTS‐Based Solar Cells: Assessment of Challenges

AbstractThe unintentional formation of a layer as a reaction product between the copper zinc tin sulfide (CZTS) thin film and the Mo back contact reduces cell efficiency due to high sheet resistance and carrier recombination. To limit the formation of , an intentionally grown p‐type Nb‐doped layer can serve as an effective hole transport layer. This study presents a detailed study and calculations for CZTS/Mo‐based solar cells, providing guidelines for calibration. Optimizing cell efficiency is influenced by various interconnected factors in Nb‐doped . While a high carrier concentration in Nb‐doped is assumed to enhance efficiency, other parameters such as band state, optical absorption, and carrier mobility also play crucial roles and can limit cell performance. This simulation study evaluated the effect of Nb‐doped layers with different carrier concentrations to determine the optimal conditions for this p‐type layer. This work reveals that a very thin layer (13 nm) of Nb‐doped p‐type can achieve a maximum efficiency of 11.34% (with = 1.5 ) and that for an Nb‐doped p‐type 62 nm is 15.82 % (with = 4.03 ).

Methyl Methacrylate Copolymer with Pendant Thioxanthenone Groups as Active Layer for Resistive Memory Devices.

An electro-active copolymer of methyl methacrylate and 2-((4-acroylpiperazine-1-yl)methyl)-9H-thioxanthene-9-one (poly(MMA-co-ThS)) was synthesized by radical polymerization. The copolymer has good solubility in most organic solvents, thermal stability up to 282 °C and excellent ability to form thin films on silicon wafers. Poly(MMA-co-ThS) films exhibited an electrochemical and electrochromic activity resulting in the formation of long-lived radical anion states of pendant thioxanthone groups inside the film. These states exhibit optical transitions in the visible region as a broad optical absorption band, 500<λ<900 nm (1.38<Wopt(ThS)<2.48 eV) with a maximum at λmax=675 nm (1.84 eV). Using temperature measurements of the current-voltage characteristics of p-Si(100)/poly(MMA-co-ThS)/Al devices, it was shown that the charge transport in the film occurs by a multiphonon mechanism, which is quantitatively described by the Nasyrov-Gritsenko model of phonon-assisted tunneling between traps. The value of the optical transition energy of the trap, determined by the Nasyrov-Gritsenko model, Wopt=1.8 eV, is in a good agreement with Wopt(ThS), confirming the nature of the traps as 9H-thioxanthen-9-one structures. The n++Si(100)/poly(MMA-co-ThS)/Al memory device exhibited a memristive effect (reversible ON/OFF switching of the device) with an initial "forming" cycle followed by repetitive memory cycles characterized by bipolar switching.

Phosphorus doped hydrogenated silicon oxycarbide: Film formation, properties and its application on silicon heterojunction solar cell

An ultrathin phosphorus doped hydrogenated microcrystalline silicon oxycarbide (n-μc-SiCO:H) layer deposited by plasma enhanced chemical vapor deposition (PECVD) method can be used as a window layer for silicon heterojunction solar cells. The optical and electrical properties of n-μc-SiCO:H films were controlled by PECVD deposition conditions. The interplay effects of H2, CO2 and PH3 to SiH4 gas ratio on the chemical composition, material structure and properties of n-μc-SiCO:H film were systematically determined. O, H, C and P atoms were observed to incorporate into the silicon network of n-μc-SiCO:H layer, while most of the atoms bond directly to Si atoms. Incorporation of oxygen and carbon atoms into n-μc-SiCO:H film, confirmed by XPS as formation of Si-O and Si-C bonds, enlarged the optical absorption band gap (Eg) value. Both film crystallinity and phosphorus concentration in n-μc-SiCO:H layer were observed to be controlled by the H2, CO2 and PH3 to SiH4 gas ratio. The electric performance of HJT solar cell was depended on the optical and electrical properties of n-μc-SiCO:H layer. An average efficiency (across ∼ 120 cells) of 26.32 % was achieved in cells with optimized deposition parameters for the n-μc-SiCO:H layer. The reaction gas ratio was also the dominant factor in determining the number and size of nanoscale Si crystallites embedded in the n-μc-SiCO:H layer. The conductivity of n-μc-SiCO:H layer was determined by the activated phosphorus concentration but independent of the total phosphorus concentration. It was also found that large concentrations of small Si crystallites of size less than 3 nm improved film conductivity.

STRUCTURES OF HDPE/GaAs AND HDPE/GaAs&lt;Te&gt; COMPOSITES IRRADIATED WITH GAMMA QUANTA

The results of optical studies of structural changes in composite HDPE/GaAs and HDPE/GaAs&lt;Te&gt; films irradiated with gamma quanta at doses of 100, 200, and 300 kGy at room temperature are presented. It was found that gamma irradiation of the initial polymer and their composite films leads to the formation of optical absorption bands at 220 and 280 nm, indicating the formation of C = 0 and C = C-bonds. It was established that composite HDPE/GaAs&lt;Te&gt; films are the most radiation-resistant in the absorbed dose range of 100…300 kGy.

First-Principles Calculations on Electronic, Optical, and Phonon Properties of γ-Bi2MoO6.

The wide band gap γ-Bi2MoO6 (BMO) has tremendous potential in emergent solar harvesting applications. Here we present a combined experimental-first-principles density functional theory (DFT) approach to probe physical properties relevant to the light sensitivity of BMO like dynamic and structural stability, Raman and infrared absorption modes, value and nature of band gap (i.e., direct or indirect), dielectric constant, and optical absorption, etc. We solvothermally synthesized wide band gap Pca21 phase pure BMO (≳3 eV) for two different pH values of 7 and 9. The structural parameters were correlated with the stability of BMO derived from elastic tensor simulations. The desired dynamical stability at T = 0 K was established from the phonon vibrational band structure using a finite difference-based supercell approach. The DFT-based Raman modes and phonon density of states (DOS) reliably reproduced the experimental Raman and infrared absorption. The electronic DOS calculated from Heyd-Scuseria-Ernzerhof HSE06 with van der Waals (vdW) and relativistic spin-orbit coupling (SOC) corrections produced a good agreement with the band gap obtained from diffuse reflectance spectroscopy (DRS). The optical absorption obtained from the complex dielectric constant for the HSE06+SOC+vdW potential closely resembled the DRS-derived absorption of BMO. The BMO shows ∼43% photocatalytic efficiency in degrading methylene blue dye under 75 min optical illumination. This combined DFT-experimental approach may provide a better understanding of the properties of BMO relevant to solar harvesting applications.

Schottky barrier diode and photoelectric device based on two dimensional noble transition-metal sulfides vertical heterojunction

In this work, we use first-principles method to investigate the properties of two-dimensional noble transition-metal sulfides MS2 (M = Ni, Pd, Pt) and the electronic and optoelectronic applications of their vertical heterojunctions. The vertically bilayer or trilayer stacking can modulate the band structures and optical absorption spectra of MS2 (M = Ni, Pd, Pt) obviously. Therefore, we create the atomically thin Schottky barrier diodes (SBD) by vertically stacking the MS2 (M = Ni, Pd, Pt) on monolayer MS2 (M = Ni, Pd, Pt). All SBDs reveal more excellent current rectification behavior along the armchair edge (AE) transport direction than that along the zigzag edge (ZE) transport direction. SBD based on PdS2 bilayer and monolayer heterojunction has the high current value and the significant rectification ratio (exceeding 105) along AE transport direction. The total photocurrent densities of all SBDs along the ZE transport direction are bigger than that along the AE transport direction. SBD based on PdS2 bilayer and monolayer heterojunction has the largest total photocurrent density (1208.07 μA/mm2) along the ZE transport direction. Our work provides foundations for the application of two-dimensional noble transition-metal sulfides in rectification and optoelectronics.

Iron borophosphate glasses: Merging optical transparency, structural integrity, and radiation shielding efficacy for sustainable uses

The research work explored the influence of iron doping on the optical behavior, structural characteristics, and radiation shielding capabilities of soda lime borophosphate glass system of composition xFe2O3-(42.5-x)B2O3-26CaO-28.7Na2O-2.8P2O5 (x up to 8 mol%). The glass samples doped with varying iron concentrations were synthesized via the conventional melt-quenching method. A comprehensive characterization approach was employed, integrating X-ray diffraction (XRD) analysis to probe the structural aspects, Fourier transform infrared (FTIR) spectroscopy to examine the molecular vibrations and bonding, and UV–visible spectroscopic techniques to investigate the optical properties. Furthermore, the study evaluated the potential of these iron-doped glasses as effective radiation shielding materials by assessing their attenuation performance against various radiation types. The influence of iron oxide (Fe2O3) addition on the borophosphate network, coordination environment, and optical absorption was examined. The radiation shielding characteristics, such as mass attenuation coefficient, half-value layer, mean free path, and other parameters, were assessed using Phy-x freeware program calculations. The results revealed the formation of an amorphous glass structure and the incorporation of iron ions into the borophosphate network. The addition of Fe2O3 influenced the borate superstructural units, the conversion of BO3 to BO4 units, and the optical absorption bands. The glasses exhibited promising radiation shielding properties combined with increasing Fe2O3 content.

Investigating structural, phonons, optoelectronics, and thermodynamic properties of lead-free double perovskites of A-site cation ordering in LiXTl2Cl6 (X= Sc and Y) compounds for green energy applications

This study explores the structural, phonons, optoelectronic, and thermodynamic properties of LiXTl2Cl6 (X = Sc and Y) compounds. These double perovskite materials are particularly interesting due to their potential for green energy applications. We employ state-of-the-art computational simulation techniques to investigate the structural properties of these compounds, focusing on the cation ordering in the A-site of the perovskite structure. Through density functional theory (DFT) calculations, we determine the equilibrium crystal structure and lattice parameters, shedding light on the stability of these materials. Furthermore, we analyze the phonon spectra to assess the materials' vibrational properties, including the presence of any phonon modes that may impact thermal stability and thermal transport. Optoelectronic properties, such as band gaps and optical absorption spectra, are also explored to evaluate the suitability of these materials for photovoltaic and light-emitting applications. We investigate their electronic structure and consider the potential for efficient charge carrier generation and transport. The thermodynamic properties, such as heat capacity, entropy, and enthalpy, are calculated to provide insight into the compounds' thermal behavior under various environmental conditions, which is crucial for green energy applications, including thermal energy conversion. This comprehensive investigation into the LiXTl2Cl6 (X = Sc and Y) compounds aims to contribute to developing lead-free double perovskite materials with tailored properties for a range of green energy applications, paving the way for more sustainable and environmentally friendly energy solutions.

Multi-objective global optimization approach predicted quasi-layered ternary TiOS crystals with promising photocatalytic properties

Abstract Titanium dioxide (TiO2) has attracted considerable research attentions for its promising applications in solar cells and photocatalytic devices. However, the intrinsic challenge lies in the relatively low energy conversion efficiency of TiO2, primarily attributed to the substantial band gaps (exceeding 3.0 eV) associated with its rutile and anatase phases. Leveraging multi-objective global optimization, we have identified two quasi-layered ternary Ti–O–S crystals, composed of titanium, oxygen, and sulfur. The calculations of formation energy, phonon dispersions, and thermal stability confirm the chemical, dynamical and thermal stability of these newly discovered phases. Employing the state-of-art hybrid density functional approach and many-body perturbation theory (quasiparticle GW approach and Bethe–Salpeter equation), we calculate the optical properties of both the TiOS phases. Significantly, both phases show favorable photocatalytic characteristics, featuring band gaps suitable for visible optical absorption and appropriate band alignments with water for effective charge carrier separation. Therefore, ternary compound TiOS holds the potential for achieving high-efficiency photochemical conversion, showing our multi-objective global optimization provides a new approach for novel environmental and energy materials design with multicomponent compounds.

Unveiling the Electronic Structure of SnS for Photocatalytic Applications: A DFT Approach†

AbstractPhotocatalytic materials are of great scientific interest due to their potential applications in sustainable energy sources. Band gap and optical absorption of the materials are two core characteristics for photocatalysis that eventually depend on electronic structure. In order to accurately compute (predict) the electronic‐scale properties of a crystalline solid using first principles calculations, which might be costly to measure experimentally, large‐scale atomic level calculation frameworks have been made possible through the use of density functional theory (DFT). We have used DFT with many body perturbation theory (MBPT) by solving the bethe‐salpeter equation (BSE) to priorly predict the properties of bulk tin sulfide (SnS) as it meets the necessary requirements for photocatalytic applications. We fixed the DFT band gap underestimation by including the Hubbard parameter (U) and used projector augmented wave pseudo‐potentials with generalized‐gradient approximation (GGA) to calculate the electronic and optical properties of SnS. Optical properties were computed using independent particle approximation (IPA) and BSE with DFT+U wave functions. Our theoretical results align with experimental data for this material, demonstrating the potential for further research in validating experimental results with theoretical approximations and empirical relations.

Modulating the electronic and optical properties of CrI3/In2Se3 van der Waals heterostructures by external fields

The van der Waals heterostructures (vdWH) composed of two-dimensional (2D) magnetic materials and non-magnetic atomic layers provide promising candidates for innovative device design. Here, we construct the CrI3/α-In2Se3 vdWH and regulate its band structure, magnetism and optical absorption through external fields. The intrinsic vdWH possesses type-Ⅱ band alignment with 0.38 eV band gap. As a result of proximity effects and superexchange interaction, magnetism is induced in the α-In2Se3 layer. The Curie temperature of the vdWH with FM coupling has increased to 99.3 K. Interestingly, with the increasing of the applied electric field, the band alignment exhibits a transition from type-Ⅱ to type-Ⅰ and then back to type-Ⅱ. When the electric field is −4.31 V/nm, the vdWH convert from semiconductor to half-metal. Moreover, the applying biaxial and vertical strain can influence the energy level of hybridization, and transferred charges. For example, the increased magnetic moment of the CrI3 monolayer increased by four times when the distance gap is decreased by 0.5 Å. These properties can offer novel strategies for engineering band structure and regulating magnetic properties, thereby enabling researchers to design tunable multiferroic vdWH devices.

Performance of long-wave infrared band of microstructured heavily doped InAsSb on type II superlattice layer part 1: the photonic study

This article deals with the optical study of nanostructured components which absorb light across the entire long-wave infrared (LWIR) spectral band. The components are made of type-II superlattice (T2SL) absorber and highly doped InAsSb, the latter being nanostructured to ensure multiple resonances. We studied two components: in the first one, the T2SL has a thickness of 1.6 μm, and in the second its thickness is 300 nm. The calculated absorption spectra were shown and the components revealed high absorption thanks to optical resonance and high angular acceptance. A fabrication process has been developed, and optical measurements have confirmed the reliability of the model.

Opto-electronic and thermophysical characteristics of A2TlAgF6 (A = Rb, Cs) for green technology applications.

Lead-free double perovskites are unique materials for transport and optoelectronic applications that use clean resources to generate energy. Using first-principle computations, this study thoroughly investigates the structural, thermoelectric, and optical attributes of A2TlAgF6 (A = Rb, Cs). Tolerance factor and formation energy estimates are used to verify that these materials exist in the cubic phase. Elastic constants with high melting temperature values are ductile when evaluated for mechanical stability using the Born stability criterion. The optical absorption band is adjusted from 2 to 4 eV via band gaps of 1.88 and 1.99 eV, as indicated by band structures. Analysis of optical properties reveals perfect absorption in the visible spectrum, whole polarization, and low optical loss. Furthermore, thermoelectric properties are assessed at 300, 500, and 700 K in the range of -0.5 to 3 eV for chemical potential (μ). The materials exhibit significant improvements in the Figure of Merit scale due to their elevated electrical conductivity, Seebeck coefficient, and extremely low thermal conductivity values.

Al, N Codoping and the Effect of O Vacancy in Photocatalyst SrTiO3

In light of the potential for enhancing SrTiO3 (STO)'s photocatalytic efficiency, particularly in the visible light region, a study is conducted on Al, N codoping in STO herein using first‐principles calculations. The effect of oxygen vacancy (VO) is also considered. It is found that AlSr, NO can significantly reduce the bandgap; however, their formation energies are rather high, and the defect levels they brought in may induce recombination centers. Under O‐deficient conditions, VO can facilitate Al, N doping in STO. When Al, N codope in STO, AlTi, NO, and VO would tend to combine, and formation of complex defect AlTi + NO + VO can further enhance N dopability in STO. Moreover, AlTi + NO + VO can simultaneously reduce the bandgap and eliminate the defect levels induced by NO. However, AlTi + NO + VO may not fully realize the potential for the photocatalytic activity due to the low optical absorption and unsuitable band alignment. The work provides a theoretical guidance for the photocatalytic performance of STO in the visible light region.

Single crystal polarization-orientation Raman spectroscopy of zeolite LTA with confined S3− anions - High dielectric constant nanoporous material

We apply polarization-orientation Raman spectroscopy, as an alternative to X-ray diffraction, to LTA single crystals containing S3− in sodalite cages additionally to S8 rings in large cavities. The sample was obtained via sulfur vapor adsorption at ∼550 °C (LTA-S-550). We show that S3− is located in the (110) plane with its 2-fold axis along the LTA 4-fold axis. The anion position suggests strong interaction of its terminal atoms with Na+ localized in LTA 6-membered rings. The anions display optical absorption band at ∼590 nm (2.1 eV) and resonant Raman enhancement. We observe a record-high S3− bond-bending mode frequency ∼274 cm−1 due to a strong bond-angle contraction. This leads to the Fermi resonance of its overtone with the symmetric bond-stretching mode in the frequency range of 544–552 cm−1. An anomalous Raman downshift of the S3− bond-stretching modes with a decrease of temperature is observed and attributed to partial compressive stress relaxation. Luminescence band at ∼845 nm is observed suggesting considering LTA-S-550 as an interesting light-emitting material. We discuss a role of S3− in the high dielectric constant up to ∼160 and a possible contribution of the anion to the ion-exchange selectivity to Sr2+/Cs+ enhancements of LTA with sulfur.

Revisiting the Quasiparticle Band Structure and Optical Properties of Few‐Layer InSe

The many‐body GW combined with the Bethe–Salpeter equation (BSE) method including the spin‐orbit coupling (SOC) effect has been adopted to revisit the band structure and optical absorption spectra evolution of single‐layer, double‐layer, three‐layer, and bulk InSe. The many‐body effect is found to play an important role in both the band structure and the optical properties of InSe structures. Not only the band gap but also the energy dispersion is influenced by the electron–electron many‐body interaction. Electron–hole interaction strongly affects the optical properties of InSe structures, especially the single‐layer InSe. Compared with previous reports, the calculations show that, including SOC, two bound excitonic peaks have emerged for monolayer InSe, with the strong bound exciton being s‐state‐like, while the other p‐state‐like. BSE also predicts abundance of bounded “dark” excitons exists for monolayer InSe, indicating that monolayer InSe is a proper platform for studying excitons. Although the spin‐orbit interaction influence on the highest valence band and the lowest conducted band seems trivial, its effect on the optical properties of InSe is remarkable.