Optoelectronic Behavior Research Articles

Investigating the optoelectronic behavior of graphene—mordant red conjugate through DFT calculations and MD simulations

Investigating the optoelectronic behavior of graphene—mordant red conjugate through DFT calculations and MD simulations

Unveiling half-metallic, thermoelectric and optoelectronic behavior of the new Heusler alloy RbCrZ (Z = Si, Ge): a DFT perspective

Abstract Utilizing the density functional theory (DFT) method, this study aims to predict with precision the structural, elastic, electronic, magnetic, thermoelectric, thermal, and optical properties of two recently discovered half-Heusler alloys, namely RbCrSi and RbCrGe. The exchange and correlation potential are accounted for using the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA-PBE) and the Tran–Blaha-modified Becke–Johnson exchange potential (TB-mBJ). Through structural analysis, it is observed that both RbCrSi and RbCrGe alloys exhibit energetic stability in a type-3 structure with a ferromagnetic (FM) state. Both alloys exhibit half-metallic properties and integer magnetic moments of 3 μB, following the Slater-Pauli rule. Additionally, elastic calculations confirm their mechanical stability and anisotropic ductile behavior. The quasi-harmonic Debye model (QHDM) is employed for calculating thermodynamic properties, while the BoltzTraP code, based on semi-classical Boltzmann theory (SCBT), is utilized for evaluating thermoelectric properties. Findings reveal that RbCrZ alloys (with Z = Si, Ge) exhibit high figure of merit (ZT) values nearing unity at highest temperature. Consequently, the newfound half-Heusler alloys RbCrSi and RbCrGe hold significant promise for applications in thermoelectricity and spintronic devices. This comprehensive analysis underscores the potential of these alloys in the realm of renewable energy applications.

Revealing Anion Exchange in Two-Dimensional Nanocrystals.

Ion exchange is a powerful postsynthesis tool for the design of functional nanomaterials. However, achieving anion exchange while maintaining the original morphology and crystal structure, as well as elucidating the mechanism, remains challenging. Here, we developed an anion-exchange strategy under mild conditions and revealed an unusual ion-exchange mechanism in the semiconductor nanoplatelets. Kinetic studies have demonstrated that the transformation follows first-order kinetics, with the ligand restricting the guest anion from diffusing only in one-dimensional directions. By monitoring the reaction process, we demonstrated that the anion exchange reaction occurs selectively on the polar surface of the NPLs and exhibits asymmetry at the two polar end faces. Theoretical simulations further confirmed that anion exchange began from the chalcogenide-dominated facet. The thermodynamic data suggest that guest ions diffuse into the crystal interior via a direct exchange mechanism. This study provides a pathway for anion exchange and the construction of functional nanocrystals and a platform for studying the optoelectronic behavior of single-sheet heterojunctions.

Disentangling the Optoelectronic Behavior of Lead Iodide Governed by Two-Dimensional Electron Confinement.

We present a joint experimental and theoretical study for complete spectroscopic characterization and optoelectronic properties of lead iodide. Experimentally, we combine X-ray diffraction experiments to elucidate the structure with photoelectron spectroscopy to explore its electronic structure. Computationally, simulations are performed in the frame of density functional theory. We show that PbI2 presents a two-dimensional layered structure and exhibits a large transient photocurrent effect under visible light illumination, which are compatible with the surface photovoltage scenario. The transient photocurrent has an extremely long lifetime: when the sample is lightened with visible light, it shows very long relaxation times and, consequently, huge charge carrier diffusion lengths. We explain this anomalous behavior with the slow carrier mobility of holes and electrons caused by the 2D electron confinement in the layered material. Our results can be used as a simple model for understanding the optoelectronic properties of more complex 2D hybrid perovskites.

Optoelectronic and Nonlinear Optical Behavior of Corner‐Functionalized Borophene Derivatives and Composites Doped with Polyaniline

Optoelectronic and Nonlinear Optical Behavior of Corner‐Functionalized Borophene Derivatives and Composites Doped with Polyaniline

Tunable Interlayer Interactions in Exfoliated 2D van der Waals Framework Fe(SCN)2(Pyrazine)2.

2D materials can be isolated as monolayer sheets when interlayer interactions involve weak van der Waals forces. These atomically thin structures enable novel topological physics and open chemical questions of how to tune the structure and properties of the sheets while maintaining them as isolated monolayers. Here, this work investigates 2D electroactive sheets that exfoliate in solution into colloidal nanosheets, but aggregate upon oxidation, giving rise to tunable interlayer charge transfer absorption and photoluminescence. This optical behavior resembles interlayer excitons, now intensely studied due to their long-lived emission, but which remain difficult to tune through synthetic chemistry. Instead, the interlayer excitons of these framework sheets can be modulated through control of solvent, electrolyte, oxidation state, and the composition of the framework building blocks. Compared to other 2D materials, these framework sheets display the largest known interlayer binding strengths, attributable to specific orbital interactions between the sheets, and among the longest interlayer exciton lifetimes. Taken together, this study provides a microscopic basis for manipulating long-range opto-electronic behavior in van der Waals materials through molecular synthetic chemistry.

Tuning the Electronic Properties of Bridged Dithienyl-, Difuryl-, Dipyrrolyl-Vinylene as Precursors of Small-Bandgap Conjugated Polymer.

Optoelectronic properties of linear π-conjugated polymers/oligomers are of great importance for the fabrication of organic photonic and electronic devices. To this end, the π-conjugated polymers/oligomers need to meet both optoelectronic and key structural properties in order to fulfill their implementation as active components. In particular, they need to possess low bandgap and high thermal, conformational, and photochemical stabilities. So far, several strategies have been developed to attain such requirements including the covalent and non-covalent rigidification concepts of the π-conjugated systems. On the basis of these findings, we describe herein the theoretical studies of novel series of covalently bridged derivatives demonstrating the benefits of the strategy. Comparison of these derivatives with compounds previously described in the literature highlights enhanced optoelectronic properties and behaviors that would be beneficial for the construction and development of new linear π-conjugated polymers.

Mapping Spatial Strain Distribution and Its Effects on Optoelectronic Properties in Wrinkled Perovskite Films.

Organic-inorganic halide perovskite films, fabricated by using the antisolvent method, have garnered intense attention for their application in high-efficiency and stable solar cells. These films characteristically develop periodic wrinkled microstructures. Previous research has indicated that macroscopic residual strain significantly influences the optoelectronic behaviors of these films. However, the detailed interplay between the wrinkled morphology, strain distribution, and local photophysical properties at the micro- and nanoscale has not been fully elucidated. Here, we explore the microscopic morphology-strain-property relationship within wrinkled perovskite films employing correlative micro-optical and nanoelectrical microscopy techniques. Microphotoluminescence (PL) mapping supplemented by in situ strain PL measurements identifies a heterogeneous spatial strain distribution across the microstructural hills and valleys. Additionally, light-intensity-dependent photoconductive atomic force microscopy reveals that valleys experiencing less compressive strain exhibit a lower conductivity and a higher propensity for ion migration. The findings underscore the potential of targeted strain engineering to optimize the performance and longevity of perovskite solar cells.

One‐Step Aerosol Synthesis of Thiocyanate Passivated Hybrid Perovskite Microcrystals: Impact of (Pseudo‐)Halide Additives on Crystallization and Access to a Novel Binary Model

AbstractHybrid Perovskite materials have gone through an astonishing development due to their unique optoelectronic behavior, leading to the creation of a wide range of synthetic strategies. As the materials’ surface is found to play a crucial role with respect to the properties, e.g. hydration, stability and carrier mobilities, considerable efforts have been made to optimize the surface through various approaches. Especially the passivation of the perovskite surface attracted a lot of attention in this field, often resulting in more complex, multi‐step synthetic processes. In this study, a simple one‐step aerosol‐assisted synthetic approach is presented to obtain thiocyanate (SCN) passivated single‐crystal MAPbBr3 microcrystals. To elucidate the role of the additive in the crystallization process, mixed (pseudo‐)halide precursors are systematically investigated. The as processed, passivated microcrystals exhibit enhanced stability and charge carrier lifetimes. Additionally, a decrease in surface photovoltage, attributed to the presence of the SCN additive, is observed. Furthermore, the aerosol process is further developed resulting in a novel binary system containing MAPbBr3‐SCN perovskite microcrystals and Au nanostructures. This system serves as a promising model for further investigations into potential interactions between plasmonic and semiconducting materials, with initial results indicating prolonged charge carrier lifetimes.

A computational approach to study optoelectronic thermoelectric behavior of ternary zinc Aluminates ZnAl2X4 (X = S, Se, Te) for low-cost energy technologies

The search for cost-effective, high-performing energy technologies has accelerated the study of new materials possessing exceptional thermoelectric qualities. This work uses a computational method to explore the thermoelectric and optoelectronic properties of ternary compounds with the goal of finding promising candidates for energy-related uses. We employ Boltzmann transport equations and density functional theory (DFT) to methodically examine the optical characteristics, electronic structure, and thermoelectric performance of ZnAl2X4 (X = S, Se, Te) compounds. The band profile reveals a semiconducting nature with direct band gap of 3.41, 3.31, 2.61 eV in ZnAl2S4, ZnAl2Se4 and ZnAl2Te4. Further, the plots of electron localization functions (ELF) provide a clear illustration of the significant hybridization of Zn-d, Al-p, and X-p states observed from the density of states. High values of optical absorbance and conductivities in UV regions confirm strong luminescent properties. The reflectance shows a red shift with increasing size and atomic no. of the chalcogenide atoms. Further, thermoelectric efficiency for these materials is estimated by calculating figure of merit values of 0.97, 0.77 and 0.716 at room temperature. Present study suggests these materials’ suitability for next-generation optical and thermoelectric devices.

Extreme high-temperature effects on optical response of CsPbBr3 perovskite

The temperature sensitivity of CsPbBr3 perovskite impacts the performance of related devices, with their optoelectronic behavior characterized by the dielectric function (ε = ε1+iε2). Yet, research on optical properties (ε) beyond 200 °C remains limited, hindering the evaluation of their high-temperature stability. This study first grew a high-quality CsPbBr3 single crystal, then examined its dielectric function from −55 to 550 °C using spectroscopic ellipsometry, and explored the optical response of all-dielectric CsPbBr3-based metasurfaces under varying temperatures. High temperature induces dynamic disorder in CsPbBr3, and thermal decomposition initiates above 300 °C, leading to a substantial change of dielectric function. CsPbBr3-based metasurfaces exhibit near-perfect light absorption (average 0.987) with only a meta-atomic height equivalent to one-seventh of the wavelength. They also demonstrate enhanced absorption at longer wavelengths, attributed to high-temperature-enhanced magnetic resonance. This work aims to improve the high-temperature performance of CsPbBr3 perovskites and expand their applications in energy and ultrafast optics.

Comparative study of the electronic and optical properties of Rhenium based Chalcogenides

Transition metal dichalcogenides are materials of growing interest due to their unique electronic properties and rich phase diagram, offering promising opportunities for various applications. In this study, we investigate the optoelectronic characteristics of two-dimensional rhenium (Re)-based chalcogenides. These materials are composed of rhenium atoms sandwiched between chalcogen layers. In this paper, we have selected three rhenium-based chalcogenide (ReS2, ReSe2 and ReTe2) compounds in their 1T structure and calculated their electronic properties. Our study aims to find the intricacies of theoretical band structures and optical properties, aiming to assess their viability as semiconducting materials for the optoelectronics industry employing density funtional theory. Furthermore, we explore the impact of varying chalcogen compositions on the optoelectronic behavior, uncovering the tunability of these materials for specific applications. The study provides insights into the role of Re-based chalcogenides as promising candidates for emerging technologies, including photodetectors, solar cells, and other optoelectronic devices. The observed band gaps highlight the potential of these materials within the infrared region of the electromagnetic spectrum. After observing optical properties derived from our calculations, we discuss the corresponding potentials of the chosen materials in optoelectronic applications.

Insight into the optoelectronic, and thermoelectric properties for zinc-based TMCs: First principle-based study

In the present study, a comparative investigation was carried out related to the structural, optical, electronic, and thermoelectric nature of three different structural phases for Zinc-based binary chalcogenide material. The newly advanced TB-mBJ (Trans-Blaha modified Becke-Johnson) scheme under the framework of the well-known density functional theory was used to obtain improved and accurate electronic properties and bandgap results. The bandgap calculations show a direct band transition nature having gap values of 1.07 eV, 1.10 eV, and 2.10 eV, for the cubic Rocksalt, the hexagonal wurtzite, and the tetragonal structures of the material respectively. The valence band maxima and the conduction band minima are both positioned at the matching Γ-point revealing a direct band type of behavior in the three studied phases. The computed total and the partial density of state visualize being shifted continuously to high values along the energy axis. The linear optical parameters the dielectric constant ε(ω), the Absorption coefficient, the Energy loss function, the Reflectivity, the Refractive indices, and Extinction coefficients are resolved in detail. The static dielectric constant ε1(0) for the corresponding, α, β and γ-phases of ZnSe decreases due to the bandgap increasing from α - γ phase with an increase in the energy above zero values. The thermoelectric nature of these three different phases is well investigated and discussed in detail. The current work can be a qualitative theoretical study associated with these different phases' structural, optoelectronic, and thermoelectric behavior and their effective technological applications.

Effect of annealing temperature on the optoelectrical synapse behaviors of A-ZnO microtube

Optoelectronic synapses with fast response, low power consumption, and memory function hold great potential in the future of artificial intelligence technologies. Herein, a strategy of annealing in oxygen ambient at different temperatures is presented to improve the optoelectronic synaptic behaviors of acceptor-rich ZnO (A-ZnO) microtubes. The basic synaptic functions of as-grown and annealed A-ZnO microtubes including excitatory postsynaptic current (EPSC), short-term memory (STM) to long-term memory (LTM) conversion, and paired-pulse facilitation (PPF), were successfully emulated. The results show that the annealing temperature of 600 °C yields high figures of merit compared to other annealed A-ZnO microtubes. The 4-fold and 20-fold enhancement dependent on the light pulse duration time and energy density have been achieved in the 600 °C annealed A-ZnO microtube, respectively. Furthermore, the device exhibited a PPF index of up to 238% and achieved four cycles of “learning-forgetting” process, proving its capability for optical information storage. The free exciton (FX) and donor–acceptor pair (DAP) concentrations significantly influenced the persistent photoconductivity (PPC) behavior of A-ZnO microtubes. Therefore, the LTM response can be controlled by the adjustment of numbers, powers, and interval time of the optical stimulation. This work outlines a strategy to improve the EPSC response through defect control, representing a step towards applications in the field of optoelectronic synaptic device.

First-principles calculation to investigate phase transition and associated changes in electronic, excitonic, and optical behavior of RbMgH3 perovskite polymorphs

Motivated by recent experimental and theoretical research on the ability to store and release hydrogen from a hydride perovskite with a large ionic character called RbMgH3, we conducted a study using density functional theory (DFT) to investigate the optoelectronic behavior of RbMgH3 in both Cubic and Hexagonal structures, as well as its phase transition.Our findings reveal that RbMgH3 exhibits an indirect band gap of 2.41 eV in the Hexagonal phase and a direct band gap of 2.15 eV in the Cubic phase. Additionally, we calculated the Gibbs energy to predict the occurrence of the phase transition. It was determined that RbMgH3 undergoes a structural transformation from Cubic to Hexagonal at a pressure of 1.78 GPa. This transition has the potential to enhance the storage kinetics of hydrogen, making RbMgH3 suitable for various applications.

Atomistic modulating of structural, elastic, and optoelectronic behavior of pure TiO2 and Fe/TiO2 for photoelectrochemical water splitting application

Titanium dioxide (TiO2) has attracted much attention because of their desirable physicochemical properties especially in the water splitting process. In this work pure and Fe-doped TiO2 compounds are studies theoretically with the help of Generalized Gradient Approximation with the revised Pardew–Burke–Ernzerh (RPBE) exchange–correlation scheme. Total Density of States (TDOS) and Partial Density of States (DOS) were analyzed in detail which show that iron (Fe) and oxygen (O) orbitals hybridize, especially in the region of the doping system conduction band minima for both modes. Additionally, this interaction produces an energy level that effectively reduces the bandgap of the adsorbed system. Optical properties were elucidated which shows that Fe-doped TiO2 system results in high absorption and photoconductivity. Moreover, the results demonstrate low bandgap energy which is suitable for the reduction in water splitting without the need for external energy. Magnetic properties demonstrated that Fe-doped TiO2 systems show very low diamagnetic responses. The calculated elastic properties of Fe-doped TiO2 indicate ductile nature of the material with a strong average bond strength. Fe-doped TiO2 exhibited less microcracks with a mechanically stable composition.

One‐Step Synthesis of Lead‐Free and Hole Transport Layer‐Free Methylammonium Bismuth Chloride ((CH3NH3)3Bi2IxCl9−x)‐Based Perovskite Solar Cells

The scientific community is moving toward a green environment using several nontoxic photon‐absorbing materials like tin, germanium, antimony, and bismuth. Bismuth halides have essential advantages like low toxicity, Earth abundance, good chemical stability, and optoelectronic behavior which make them suitable for lead‐free perovskite solar cells. Herein, a streamlined one‐step spin‐coating technique is employed using DMF to enhance the morphology of thin films based on BiCl3 perovskite. The resulting thin films of methylammonium bismuth halide ((CH3NH3)3Bi2IxCl9−x) display a remarkably uniform, pinhole‐free, and finely nanostructured morphology, ensuring consistent surface coverage. For the development of hole conductor‐free Bi‐perovskite solar cells (PSCs), carbon is utilized as both counter electrode and hole extraction layer. The device configuration entails FTO/Compact TiO2/meso‐TiO2/((CH3NH3)3Bi2IxCl9−x)/Carbon/FTO, a novel arrangement for Bi‐PSCs. Notably, the fabricated devices demonstrate commendable photovoltaic properties, including Voc of 280 mV, Jsc of 0.25 mA, fill factor of 0.60, and a notably elevated power conversion efficiency (PCE) of 0.042% which has proven significantly advantageous in achieving higher PCE. Furthermore, the fabricated devices exhibit robust chemical stability over 40 d when exposed to an ambient atmosphere without encapsulation. The solar cells retain 25% of their initial PCE after 168 h, further highlighting their durability and suitability for practical applications.

Effects of palladium doping on structural, mechanical，and opto-electronic behavior of Cs2Pt1-xPdxBr6 double perovskites

Stability in structure and mechanical properties, along with an appropriate band structure, plays a pivotal role in enhancing the performance of the absorber layer materials in perovskite solar cells. In this study, we have employed first-principles calculations to explore the effects of palladium (Pd) doping on the structural, mechanical, and optoelectronic properties of Cs2PtBr6 perovskite. The aim is to explore and identify absorber layer materials for solar cells with superior physical characteristics. Results demonstrated that pristine and Pd4+ doped Cs2PtBr6 are mechanically and dynamically stable, and they all belong to ductile materials. Electronic structure calculations show that Pd4+doping can induce the transition of Cs2PtBr6 from an indirect bandgap to a direct bandgap. Concurrently, with the increase of Pd4+doping concentration, the bandgap decreases, which is beneficial for light absorption. Optical property analyses have also confirmed that with the increase in Pd4+ doping concentration, there is a significant improvement in the optical absorption of Cs2PtBr6 within the visible light range. Particularly, double perovskite Cs2Pt0.25Pd0.75Br6 and Cs2PdBr6 stand out as the best candidates for the solar cell absorption layer due to their close proximity to the ideal bandgap (∼1.5 eV) and strong light absorption coefficients (exceeding 105 cm−1). The findings contribute to the development of light absorption layer materials in perovskite solar cells.

Structural, optoelectronic, and magnetic behaviors of Li2BeTM (TM = V, Cr, Mn, Fe) Se4 compounds using DFT investigations

In this work, we present computational investigations of the electronic, the optical and the magnetic properties of the Li2BeTMSe4(TM = V, Cr, Mn, Fe) compounds using the first-principle calculations based on the density functional theory. In this respect, we employ the generalized gradient approximation corrected by the Tran-Balaha modified Becke-Johnson exchange potential to obtain more accurate results. Among these outcomes, we first study the electronic properties such as the band energy dispersion and the state densities. Regarding this, the Li2BeTMSe4 quaternary family is found to have an indirect band gap of 1.910 eV, 1.905 eV, 2.223 eV and 1.278 eV for TM = V, Cr, Mn, and Fe, respectively. Further, an examination of the optical properties reveals that the computed optical absorption spectra cover a broad energy range in the visible and the ultraviolet spectrums. Motivated by spintronic applications, we additionally determine the total and the local magnetic moments. Then, we compute the associated Curie temperatures via a linear relation with the total magnetic moments. Among others, the Li2BeTMSe4(TM = V, Cr, Mn, Fe) materials involve acceptable temperatures showing potential applications for high temperature nano-devices activities. Comparing the obtained findings with the available ones, the acquired results indicate that the Li2BeTMSe4(TM = V, Cr, Mn, Fe) materials exhibit a wide range of applications in solar cells, optoelectronics, and other fields.

Photoprogrammed Multifunctional Optoelectronic Synaptic Transistor Arrays Based on Photosensitive Polymer-Sorted Semiconducting Single-Walled Carbon Nanotubes for Image Recognition.

The development of neuromorphic optoelectronic systems opens up the possibility of the next generation of artificial vision. In this work, the novel broadband (from 365 to 940nm) and multilevel storage optoelectronic synaptic thin-film transistor (TFT) arrays are reported using the photosensitive conjugated polymer (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(bithiophene)], F8T2) sorted semiconducting single-walled carbon nanotubes (sc-SWCNTs) as channel materials. The broadband synaptic responses are inherited to absorption from both photosensitive F8T2 and sorted sc-SWCNTs, and the excellent optoelectronic synaptic behaviors with 200 linearly increasing conductance states and long retention time >103s are attributed to the superior charge trapping at the AlOx dielectric layer grown by atomic layer deposition. Furthermore, the synaptic TFTs can achieve IOn/IOff ratios up to 106 and optoelectronic synaptic plasticity with the low power consumption (59aJ per single pulse), which can simulate not only basic biological synaptic functions but also optical write and electrical erase, multilevel storage, and image recognition. Further, a novel Spiking Neural Network algorithm based on hardware characteristics is designed for the recognition task of Caltech 101 dataset and multiple features of the images are successfully extracted with higher accuracy (97.92%) of the recognition task from the multi-frequency curves of the optoelectronic synaptic devices.