Candidates For Optoelectronics Research Articles

Centimeter-scale single-crystal hexagonal boron nitride freestanding thick films as high-performance VUV photodetectors

Large-scale hexagonal boron nitride (h-BN) single crystals are highly desirable not only as the substrate or dielectric for van der Waals heterostructures, but also the promising candidates in optoelectronics, electronics, detectors, as well as recently boomed room-temperature single-photon sources. Here, we report the synthesis of centimeter-scale single-crystal h-BN films with hundreds of micrometer thickness via the metal flux method. The growth control along the out-of-plane and in-plane directions of h-BN crystals is realized by the adjustment of NiCr alloy composition, from which the limited solubility of N atoms can be promoted by high diffusion in molten reactants. This also benefits to forming a distinct interface between the synthesized h-BN crystals and the metal ingot, giving rise to an easy exfoliation of the large area high-quality thick films. Such h-BN crystals have been demonstrated as both self-powered flexible and rigid vacuum-ultraviolet photodetectors, allowing for efficient photodetection in terms of high responsivity, rapid response speed, and high operational temperature. A maximum photoresponsivity of 3.35 mA/W is achieved at a wavelength of 185 nm with an operational temperature spanning to 500 °C (and possibly beyond). The large-area freestanding h-BN single crystal described herein reveals great potential as a high-performance photodetector, and versatile platform for other superb electronic and optoelectronic devices.

An Insight into the Impact of Nano CuCo2O4 Doping on the Optical and Dielectric Performance of PMMA/Carbon Nanoparticles

In the present study, novel functional properties were achieved for polymethyl methacrylate (PMMA) through loading with carbon nanoparticles (CNPs) as well as varying quantities of CuCo2O4 nanoparticles. The blends obtained were subjected to different characterization techniques. Extensive investigations of different optical properties were carried out, covering linear and nonlinear optical properties. After the incorporation of CNPs/CuCo2O4 in the host polymer matrix, the absorbance, reflectance and refractive index exhibited improvements, while continuous reductions in both direct and indirect optical band gap energies were observed. Significant improvements in the linear and nonlinear optical parameters were observed with increasing CuCo2O4 doping levels. Dielectric measurements provided insights into the impact of CuCo2O4 content on the ac conductivity, energy density, dielectric properties, and electric modulus across all blends. The sample doped with 1.5 wt% exhibited the highest dielectric constant. In conclusion, the optical and dielectric properties of the PMMA/CNPs/x wt% CuCo2O4 blends make them promising candidates in optoelectronics and photocatalysis applications.

Tailoring the optical properties of polyvinyl alcohol-polyvinyl pyrrolidone based polymers

In this work, new polymeric based films are fabricated and optically characterized. The new films include poly(vinyl alcohol), plain and blended with poly(vinyl pyrrolidone), comprising glycerin, and acetic acid,as additives. XRD and FTIR analysis were conducted to give insight into the structure of the films. The reflectance and transmittance for these films are measured in the UV–vis–NIR regions. Using these measurements, the refractive index, the permittivity and many other optical constants are retrieved. The results reveal that the fabricated films possess an extinction coefficient that is almost 3 times less, and a refractive index that is 0.1 higher than plain PVA in the telecommunications wavelength range. Besides, a noticeable increase in the refractive index of the films is achieved, up to 0.35 higher compared with silicon dioxide at the near infrared spectral region. Moreover, when compared to silicon and Germanium, in the ultraviolet and visible spectral region, a substantial reduction of 3 to 4 orders of magnitudes in extinction coefficient is achieved, in the favor of the investigated films. Interestingly, the films also show small dispersion over a wide range of wavelength. Therefore, the newly proposed films can be candidates for optoelectronics, solar cells, and integrated optics applications where high refractive index and low loss are desired for high density of fabrication.

Thermal annealing induced linear/nonlinear properties of Ag2S/As2Se3 heterojunction films for optoelectronic applications

The present study reports the annealing induced structural as well as optical properties of Ag2S/As2Se3 heterostructure film at different annealing temperatures. The trigonal AgAsSe2 phase formation was confirmed from the X-ray diffraction (XRD) and selective area electron diffraction (SAED) study. The bandgap of as-prepared Ag2S/As2Se3 film decreased on annealing. The reduction in bandgap increased the static refractive index with annealing. The Urbach energy increased from 422±3 meV to 464±2 meV whereas the optical density and extinction coefficient increased by annealing due to the formation of AgS–AsSe solid solution. The dispersion energy increased and consequently increased the oscillator wavelength and oscillator strength upon annealing. The carrier concentration and optical conductivity increased whereas the optical electronegativity decreased with annealing. The 3rd order nonlinear susceptibility (χ(3)) increased from 2.804x10−11 esu (as-prepared Ag2S/As2Se3) to 5.132 x10−11 esu upon annealing at 200 °C. The n2 value increased upon annealing which increased the nonlinear absorption coefficient but decreased the figure-of-merit. The contact angle value decreased (93°–47.6°) that shows the transformation of hydrophobicity to hydrophilic nature which is good for sensor applications like biological sensor. The surface roughness decreased upon annealing. The change in optical parameters upon annealing makes them the appropriate candidate for optoelectronics, dielectric and nonlinear optical applications such as memory devices, optical switch, etc.

Ab-initio calculation of the structural, electronic, mechanical, optical, and thermoelectric properties of orthorhombic ZnAs compound

First-principles calculations of the structural, electronic, elastic, optical, and thermoelectric properties of the ZnAs compound have been investigated using density functional theory (DFT). To figure out the structural and mechanical properties, we used the generalized gradient approximation of Perdew-Bruke-Ernzerhof (PBE-GGA). Our computed structural properties are closely aligned with experimental values. The elastic constants have verified the mechanical stability of the ZnAs compound and also showed that the latter is stiff and brittle, confirming its semiconducting behavior. Furthermore, we used the modified Beck and Johnson (TB-mBJ) potential to study the band structure and density of state, which revealed that ZnAs is a semiconductor compound with an indirect band gap. The optical characteristics of ZnAs show that it can be used as a candidate for optoelectronics since it has high optical conductivity. Finally, our compound is a good thermoelectric material with a high-power factor and a figure of merit close to unity (0.98 at 300 K and 0.91 at 1000 K).

Structures, stabilities, optoelectronic and photocatalytic properties of Janus aluminium mono-chalcogenides Al(Ga, In)STe monolayers

Computational design of new two-dimensional materials constitutes an effective and promising approach in the development and exploration of a wide range of emerging applications such as optoelectronics, photocatalysis, energy storage, and conversion. Within the framework of this work, we systematically investigated for the first time, the structural, stability, optoelectronic, and pho-tocatalytic properties of new predicted Al(Ga, In)STe monolayers derived from Janus Aluminium mono-chalcogenides through Density Functional Theory and Ab-Initio molecular dynamic simulations. After a full optimization of both struc-tures, their dynamics and thermal stability was confirmed through the calculations of phonon spectrum and ab-initio molecular dynamics at a chosen temperature, respectively. Subsequently, the electronic and optical properties were explored and findings revealed that both monolayers exhibit a semiconducting characteristic with a direct and indirect electronic band gap of about 2.23 and 2.69 eV using HSE06 hybrid functional for AlGaSTe and AlInSTe monolayers, re-spectively. Furthermore, the optical absorption indicates a strong absorption of light in the range between 3 and 18 eV. More noticeably, Both Janus monolayers considered exhibiting a promising optical absorption in the visible wavelength region with an absorption coefficient greater than 105 cm−1. In addition, the photocatalytic properties of these structures were investigated by plotting the band edge positions straddle the reduction potential of H2 and the oxidation potential H2O. Based on our results, we conclude that both monolayers offer good thermodynamic stability allowing them to be processed experimentally and can be used as very appropriate candidates for optoelectronics and photocatalytic applications.

Investigations of Lead Free Halides in Sodium Based Double Perovskites Cs2NaBiX6(X=Cl, Br, I): an Ab Intio Study

Despites the excellent merits of lead based perovskite optoelectronic devices; their unstable nature and toxicity still present a bottleneck for practical applications. Double perovskite has emerged as a candidate for optoelectronics and photovoltaic application because of its nontoxic behaviour and stability in air. We have presented ab-initio study of Cs2NaBiX6(X=Cl, Br, I) lead free halide double perovskites. The calculation is carried out using the FP-LAPW method in the DFT framework within PBE potential using the WIEN2k code. The structural, electronic and optical properties of Cs2NaBiI6, Cs2NaBiBr6 and Cs2NaBiCl6 have been analysed. We have obtained the band gap of 2.0, 2.6 and 3.7 for Cs2NaBiI6, Cs2NaBiBr6 and Cs2NaBiCl6 respectively. Throughout the study, we have shown that the variation in the structure of double perovskite within Cs2NaBiX6(X=Cl, Br, I) that leads to the variation in band gap, density of states and in optical properties such as extinction coefficient, absorption spectra, optical reflectivity, dielectric coefficient, refractive index that shows the variety of this material for optoelectronic devices and other purposes.

Internal–External Stabilization Strategies Enable Ultrastable and Highly Luminescent CsPbBr3 Perovskite Nanocrystals for Aqueous Fe3+ Detection and Information Encryption

AbstractThe high photoluminescence quantum yield (PLQY) of perovskite nanocrystals (PNCs) makes them promising candidates in optoelectronics. However, the easy loss of structural integrity and fast chemical degradation upon exposure to moisture influence their reliable applications in aqueous solutions. Here, a hierarchical surface construction strategy is rationally designed to fulfill an internal–external stabilization of PNCs. Carbon quantum dots (CQDs) and cetyltrimethyl ammonium bromide (CTAB) have been demonstrated stabilized PNCs internally by eliminating the proton transfer‐induced ligand desorption. Meanwhile, CTAB acts as a cationic surfactant in consolidating the subsequent SiO2 coating to prevent the PNCs from external environments. Based on the resulted PNCs, a sensitive and selective fluorescence film sensor for Fe3+ detection is successfully constructed. The fluorescence of PNCs at 525 nm is quenched after the addition of Fe3+ in the concentration range from 770 pm to 411 µm. As Fe3+ ions attached to the surface of the film are removed with water, the fluorescence of the film can be easily recovered. Owing to this character, the application of the PNCs toward the confidential information encryption has been proved. This work provides an effective design strategy to improve the stability of PNCs and extends their applications in sensing and encryption areas.

Inorganic Ruddlesden-Popper Faults in Cesium Lead Bromide Perovskite Nanocrystals for Enhanced Optoelectronic Performance.

While the layered hybrid Ruddlesden-Popper (RP) halide perovskites have already established themselves as the frontrunners among the candidates in optoelectronics, their all-inorganic counterparts remain least explored in the RP-type perovskite family. Herein, we study and compare the optoelectronic properties of all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) with and without RP planar faults. We find that the RP-CsPbBr3 PNCs possess both higher exciton binding energy and longer exciton lifetimes. The former is ascribed to a quantum confinement effect in the PNCs induced by the RP faults. The latter is attributed to a spatial electron-hole separation across the RP faults. A striking difference is found in the up-conversion photoluminescence response in the two types of CsPbBr3 PNCs. For the first time, all-inorganic RP-CsPbBr3 PNCs are tested in light-emitting devices and shown to significantly outperform the non-RP CsPbBr3 PNCs.

Progress and perspective in Dion-Jacobson phase 2D layered perovskite optoelectronic applications

2D organic-inorganic halide perovskites have recently become the “next big thing” as promising candidates in optoelectronics. They possess higher moisture stability and lower ion migration compared to 3D perovskites due to the incorporation of bulky organic spacers. Compared to 2D Ruddlesden-Popper (RP) phase with two monoammoniums, 2D Dion-Jacobson (DJ) phase containing one diammonium has achieved a tighter connection between inorganic sheets due to formation of hydrogen bonds, resulting in higher crystal stability and more favorable charge transfer. RP phase solar cell has increased from 4.73% to 18.24% within six years, whereas DJ phase device shows a steep efficiency rise from 7.32% to 17.9% within only one year. Herein, this review provides in-depth understandings on optical property, orientation and charge transport, and energy band alignment of DJ phase perovskites, and raise perspectives that how they are affected by n value and diammoniums characteristics. The recent advances in solar cells, light-emitting diodes, and photodetectors have also been summarized. Finally, we discuss the remaining challenges of boosting device efficiency and try to answer the key scientific question that how to narrow phase distribution and engineer vertical orientation achieving the favorable energy alignment.

Polarized Photoluminescence from Lead Halide Perovskites

AbstractSolution‐processable lead halide perovskites possess excellent optical and electronic properties as one of the best candidates for optoelectronics. Especially, some of the perovskites show high quantum efficiency in photoluminescence, which enables their promising application in next‐generation light‐emitting materials and devices. More interestingly, the highly crystalline nature of perovskites as well as the intrinsic spin selectivity of exciton transitions introduces fascinating polarization properties into the light emission from lead halide perovskites. Herein are summarized the recent advances in the studies of polarized photoluminescence from lead halide perovskites in terms of both in‐depth understanding and potential application. The bright excitons in perovskite materials provide spin sublevels that give rise to radiative transitions carrying angular momentum, which is essential for the observation of polarized light emission. The polarization in photoluminescence can be amplified or modulated by introducing functional units such as chiral ligands in the chemical components of perovskites. Incorporating highly ordered microstructures into the perovskite materials is proved to be an effective way to further enhance the polarization properties at the macroscopic scale. The chemical and structural versatility of lead halide perovskites allows utililization of their characteristics of optical polarization in the construction of light sources, photodetectors, display devices, and so on.

Pressure induced semimetal to metal transition in MoTe2-xSex and WTe2-xSex

Abstract Two-dimensional transition metal dichalcogenides (TMDCs) are an emerging class of materials that make them eligible for diverse applications. Moreover, the capability of tuning electronic properties under extreme conditions create rich physics and hold them as candidates for optoelectronics, spintronics and nanoelectronics. We executed density functional theory (DFT) to address the electronic properties of MoTe2-xSex and WTe2-xSex with x = 1 under pressure. Both the compounds reveal a semimetallic property at ambient pressure. The electronic character of the band structure and density of states (DOS) exhibit a metallic transition near 3 GPa for both the compounds MoTeSe and WTeSe. The present work depicts a pressure studies up to 10 GPa to explore the lattice parameters, volume changes and c/a anomaly. WTeSe shows a Dirac like dispersion without any band crossings along Z-U symmetry path.

Improvement of the thermal stability and optical properties for poly (ortho phenylene diamine) using soft templates

A crystalline protonated-poly (ortho phenylenediamine) microrods [POPDA] with ladder-type structure was elaborated at room temperature in an acidic medium. The synthesis method was based on an oxidative polymerization, including sodium dodecyl sulphate [POPDA-SDS] and glycine [POPDA-Gly]. In case of absence or soft template presence, thin films from the considered polymers were fabricated by physical vapor deposition (PVD). Both the resulting polymer flakes and prepared thin films were studied via different techniques such as XRD, FTIR, TGA, SEM, UV–Vis, while optical properties are discussed in detail. The optimization of the samples was performed using Cambridge Serial Total Energy Package (CASTEP) program and density functional theory (DFT) by DMol3. Structural properties of resulting polymers were determined by XRD and FT-IR analysis. XRD results of thin films showed (Monoclinic 2) crystal structure and showed an increase in crystallite size for the polymer, prepared in the presence of SDS surfactants. The surface morphology study revealed the existence of a smooth surface with a significant number of uniform microrods. The optical calculation showed that absorption index k, refractive index n, dielectric constants, and optical conductivity decrease with photon energy increase. The optical properties of simulated FTIR, XRD, and CATSTEP of the considered polymers present a respectable level of experimental study agreement. The polymer thin films present a promising case to be the right candidate for optoelectronics and solar cell applications.

Novel two-dimensional monoelemental and ternary materials: growth, physics and application

Abstract Two-dimensional (2D) materials have undergone a rapid development toward real applications since the discovery of graphene. At first, graphene is a star material because of the ultrahigh mobility and novel physics, but it always suffered from zero bandgap and limited device application. Then, 2D binary compounds such as transition-metal chalcogenides emerged as complementary materials for graphene due to their sizable bandgap and moderate electrical properties. Recently, research interests have turned to monoelemental and ternary 2D materials. Among them, monoelemental 2D materials such as arsenic (As), antimony (Sb), bismuth (Bi), tellurium (Te), etc., have been the focus. For example, bismuthene can act as a 2D topological insulator with nontrivial topological edge states and high bulk gap, providing the novel platforms to realize the quantum spin-Hall systems. Meanwhile, ternary 2D materials such as Bi2O2Se, BiOX and CrOX (X=Cl, Br, I) have also emerged as promising candidates in optoelectronics and spintronics due to their extraordinary mobility, favorable band structures and intrinsic ferromagnetism with high Curie temperature. In this review, we will discuss the recent works and future prospects on the emerging monoelemental and ternary materials in terms of their structure, growth, physics and device applications.

Green Emission Induced by Intrinsic Defects in All-Inorganic Perovskite CsPb2Br5.

All-inorganic perovskites with improved stability are expected to be better candidates for optoelectronics, compared to organic-inorganic hybrid perovskites. A new member of all-inorganic perovskites, CsPb2Br5, has attracted great attention for its promising applications in optoelectronic devices. However, the origins of the green emission in CsPb2Br5 have been actively debated. By using first-principles calculations, we find that CsPb and VBr are dominant intrinsic defects independent of the growth conditions within the stable region of CsPb2Br5. Interestingly, we suggest that individual intrinsic defects do not lead to the green emission of CsPb2Br5, while the donor-acceptor pair recombination of CsPb and VBr possibly does. Our findings provide new insights into the experimental controversy about the green emission and its origins in CsPb2Br5 from the perspective of intrinsic defects, which help to extend the application of CsPb2Br5 in optoelectronic devices.

Strain effect on SnS2 nanoribbons: Robust direct bandgap of zigzag-edge and sensitive indirect semiconductor with armchair-edge states

First-principles calculations are used to study the electronic properties and strain effect on the SnS2 nanoribbons with zigzag- and armchair-terminated edge states. Theoretical results show that bandgaps of both types of nanoribbons decrease monotonically with the increasing ribbon width. The indirect bandgap characteristic is reserved in ANRs, while ZNRs turn into direct bandgap semiconductors. Applying the uniaxial strain, the bandgap of 13-ANR is sensitive and can be modified significantly, while the 8-ZNR exhibits a 2.1eV robust direct bandgap at X point. Our calculations indicate that zigzag-edged SnS2 nanoribbons can be potential candidates in optoelectronics and photocatalyst.

Upconversion Modulation through Pulsed Laser Excitation for Anti-counterfeiting

Lanthanide-doped upconversion nanomaterials are emerging as promising candidates in optoelectronics, volumetric display, anti-counterfeiting as well as biological imaging and therapy. Typical modulations of upconversion through chemical methods, such as controlling phase, composition, morphology and size enable us to rationally manipulate emission profiles and lifetimes of lanthanide ions by using continuous-wave laser excitation. Here we demonstrate that under pulsed laser excitation the emission color of NaYF4:Er/Tm (2/0.5%)@NaYF4 core-shell nanoparticles has an obvious transformation from green to red colors. Moreover, both pulse duration and repetition frequency are responsible for manipulating the upconversion emission color. The mechanism of the phenomena may be that the pulsed laser sequence triggers the emission levels to non-steady upconversion states first, and then cuts off the unfinished population process within the pulse duration. This pump source dependent and resultant tunable fluorescence emission enables NaYF4:Er/Tm (2/0.5%)@NaYF4 nanoparticles as a promising fluorophore in the transparent anti-fake printing.

Near-Infrared Luminescence from Sol−Gel Materials Doped with Holmium(III) and Thulium(III) Complexes

A series of ternary Ln(tta)3L complexes (Ln = Ho, Tm; Htta = 2-thenoyltrifluoroacetone; L = 1,10-phenanthroline, 2,2′-bipyridine, or triphenyl phosphate oxide) and their corresponding sol−gel hybrid materials formed via the in situ synthesis process (designated as Ln-T-L gel) were reported. The complexes and the gels were studied in detail, which suggest the complexes have been successfully synthesized in the corresponding gels. After excitation at the maximum absorption of the ligands, the complexes and the gels all show the characteristic near-infrared (NIR) luminescence of the corresponding Ln3+ ions, which is due to efficient energy transfer from the ligands to the central Ln3+ ions via an antenna effect. The radiative properties of the Ho3+ ion in the Ho-T-B gel are discussed by Judd-Ofelt analysis, indicating that the 5F5 → 5I6 transition of the Ho3+ ion in the Ho-T-B gel could be a possible candidate for optoelectronics.