New Types Of Optoelectronic Devices Research Articles

Effect of fluorination on properties of thiophene-phenylene co-oligomers with annulated core: a DFT study

Organic light-emitting transistors are a new type of optoelectronic devices that combine the functionality of OLED and a transistor that controls it. The working layer of these devices requires organic semiconductors that combine high charge mobility with a high photoluminescence quantum yield. One of the promising classes of such materials are thiophene-phenylene co-oligomers, the properties of which can be tuned over a wide range by adding various substituents. In this work, we address the effect of fluorination on the properties of two model thiophene-phenylene co-oligomers with an annulated central fragment, P–TTA–P and P–BTBT–P. It is shown that fluorination of both molecules lowers their frontier orbitals energy levels, and this should enable electron transport in their crystals and films. At the same time, fluorination has a qualitatively different effect on the delocalization of frontier orbitals, the width of the optical gap, the oscillator strength, the exciton binding energy, and the Raman spectrum, which is explained by the difference in the equilibrium geometry of fluorinated molecules. It is expected that the revealed relationships between the structure and properties of the studied compounds will contribute to the rational design of organic semiconductors for efficient light emitting devices.

Electric-Field-Driven Trion Drift and Funneling in MoSe2 Monolayer.

Excitons, electron-hole pairs in semiconductors, can be utilized as information carriers with a spin or valley degree of freedom. However, manipulation of excitons' motion is challenging because of their charge-neutral characteristic and short recombination lifetimes. Here we demonstrate electric-field-driven drift and funneling of charged excitons (i.e., trions) toward the center of a MoSe2 monolayer. Using a simple bottom-gate device, we control the electric fields in the vicinity of the suspended monolayer, which increases the trion density and pulls down the layer. We observe that locally excited trions are subjected to electric force and, consequently, drift toward the center of the stretched layer. The exerting electric force on the trion is estimated to be 102-104 times stronger than the strain-induced force in the stretched monolayer, leading to the successful observation of trion drift under continuous-wave excitation. Our findings provide a new route for manipulating trions and achieving new types of optoelectronic devices.

Advance and prospect of metal-organic frameworks for perovskite photovoltaic devices

Improving the long-term stability is now one of the most critical challenges in perovskite photovoltaic devices. Recently, metal-organic frameworks (MOFs) with appreciable chemical and moisture stabilities are increasingly used in optoelectronics devices. The introduction of MOFs into perovskite solar cells has paved an innovative way to address the stability issue. Consequently, the combination of perovskite photovoltaics with MOFs has drawn significant research interest in the perovskite community not only due to the enhanced stability but also for the improved photovoltaic performance resulting from the reduced defect concentration, increased charge-carrier transport, and effective energy-band alignment. This review focuses on the development of MOF-assisted perovskite photovoltaic devices and systematically summarizes the recent progress in this new type of optoelectronic device upon the combination of MOFs and perovskite photovoltaics. We have critically analyzed various functions of MOFs, including individual interlayer, a modifier of the interlayer, and MOFs/perovskite heterojunction. Furthermore, we provide a roadmap about the potential challenges and prospects of MOF-based perovskite solar cells. • Metal-organic frameworks (MOFs) with appreciable chemical and moisture stabilities are increasingly used in optoelectronics devices. • The combination of perovskite photovoltaics with MOFs has drawn significant research interest in the perovskite community not only due to the enhanced stability but also for the improved photovoltaic performance. • Various functions of MOFs, including individual interlayer, a modifier of the interlayer, and MOFs/perovskite heterojunction, have been critically analyzed.

Effect of vertical strain and in-plane biaxial strain on type-II MoSi2N4/Cs3Bi2I9 van der Waals heterostructure

Construction of van der Waals heterostructures (vdWHs) from layered materials may form new types of optoelectronic devices with better performance compared to individual layers. Here, we investigate theoretically the structural stability, electronic properties, charge-transport mechanisms, and optical properties of two-dimensional (2D) MoSi2N4/Cs3Bi2I9 vdWHs by using the first-principles calculations. Our results demonstrate that the 2D MoSi2N4/Cs3Bi2I9 vdWHs possess a direct bandgap and type-II band alignment due to the built-in electric field induced by the electron transfer from MoSi2N4 to Cs3Bi2I9 layer, which can prevent photoinduced electrons and holes from recombination and thus enhance the carrier lifetime. Furthermore, the optical absorption of the heterostructure is enhanced in the visible and ultraviolet region, and its electronic property is tunable under in-plane strains with a clear metal–semiconductor transition. Finally, we explore more A3B2X9/MA2Z4 vdWHs with A = Cs; B = In, Sb, Bi; and X = Cl, Br, I in A3B2X9 and M = Cr, Mo, Ti; A = Si; and Z = N, P in MA2Z4, and we find all three types of band alignments (type-I, type-II, and type-III). Our study provides a comprehensive theoretical understanding of the electronic and optical properties of perovskite-based heterostructures and indicates its potential applications in optoelectronic devices.

New selection rule of resonant Raman scattering in MoS2 monolayer under circular polarization

• The first-order resonant Raman spectra of monolayer MoS2 under the circularly polarized photoexcitation is re-visited based on the first-principles density functional theory calculation. • The anomalous selection rule for the two-dimensional mode appears under high-energy laser excitation, revealing a certain correlation with valley selectivity of helical optical absorption. • The Raman anomaly can also be understood from the calculated Raman tensor, and supports the pseudo-angular-momentum conservation law. • This study may shed a light on the new understanding of the unconventional phenomenon and help new functional design for applications in helicity related optoelectronics. The first-order resonant Raman spectra of monolayer MoS 2 are calculated under the circularly polarized photoexcitation. The anomalously nonzero Raman intensity of the in-plane E mode under the Z ¯ ( σ + σ + ) Z or Z ¯ ( σ − σ − ) Z geometry, which goes against the conventional selection rule, appears under some circumstances when optical absorption occurs at some special reciprocal points between the zone-center Γ and the zone-edge-center M points. At that moment, the valley selectivity to the circular polarization is lifted. The analysis shows that the anomalous Raman intensity of the E mode for the same circularly polarized incident and scattered light is consistent with the pseudo-angular-momentum conservation law. The calculated E Raman tensor of monolayer MoS 2 is found to vary with laser energy. The two diagonal terms of the Raman tensor change their signs from mutually opposite to the same when the relative intensity of the in-plane E mode to the out-of-plane A 1 ′ mode increases, indicating the increasingly important role played by the Frölich-type electron-phonon interaction over the deformation potential. Our study may shed new light on the understanding of the novel electron-photon process and assist in the design of new type of optoelectronic devices.

Light-emitting field-effect transistors with EQE over 20% enabled by a dielectric-quantum dots-dielectric sandwich structure

Emerging quantum dots (QDs) based light-emitting field-effect transistors (QLEFETs) could generate light emission with high color purity and provide facile route to tune optoelectronic properties at a low fabrication cost. Considerable efforts have been devoted to designing device structure and to understanding the underlying physics, yet the overall performance of QLEFETs remains low due to the charge/exciton loss at the interface and the large band offset of a QD layer with respect to the adjacent carrier transport layers. Here, we report highly efficient QLEFETs with an external quantum efficiency (EQE) of over 20% by employing a dielectric-QDs-dielectric (DQD) sandwich structure. Such DQD structure is used to control the carrier behavior by modulating energy band alignment, thus shifting the exciton recombination zone into the emissive layer. Also, enhanced radiative recombination is achieved by preventing the exciton loss due to presence of surface traps and the luminescence quenching induced by interfacial charge transfer. The DQD sandwiched design presents a new concept to improve the electroluminescence performance of QLEFETs, which can be transferred to other material systems and hence can facilitate exploitation of QDs in a new type of optoelectronic devices.

Spin Hall effect of Laguerre-Gaussian beams in PT symmetric metamaterials

Spin Hall effect (SHE) of Laguerre-Gaussian (LG) beams reflected and transmitted in parity-time (PT) symmetric metamaterials are investigated near the coherent-perfect-absorption (CPA)-laser point and exceptional points (EPs). The numerical results show that large transverse shifts occur at the CPA-laser point regardless of the incident direction. But at EPs, the SHE increases at one side and disappears at the other side, thus achieving the intense SHE of the reflected light beams at the specified side incidence. In addition, it is found that Bragg oscillation can be generated by increasing the period number of PT symmetric metamaterial layers, thus increasing the number of formants in transverse displacement. In particular, the transverse shift peaks of the transmitted beams merge into a positive peak when the incident angle is close to 90∘ and does not change basically with the increasing of Im(ɛ), which can also be considered as a strong tolerance to the variation of Im(ɛ). This feature is expected to realize a new type of optoelectronic devices with anti-interference performance. These results provide a feasible path for the modulation of spin Hall effect of light (SHEL) and provide the possibility for the development of new nanophotonic devices.

Structural Effect of Perylene Derivatives on Their Interaction with Reduced Graphene Oxide Monolayers

The elucidation of factors influencing energy transfer in hybrid systems based on organic sensitizers and two-dimensional carbon materials is an important problem of thin-film chemistry, whose solution will make it possible to rationalize the design of new type of optoelectronic devices. The role of substituents in a perylene molecule in the energy transfer between a chromophore and a reduced graphene oxide (GO) monolayer was eludicated by Raman spectroscopy. It was shown that the adsorption of a perylene derivative with a planar geometry on reduced GO leads to fluorescence quenching and enhances Raman scattering in the chromophore. At the same time, no Raman bands from perylene can be detected after a “planar” chromophore is immobilized on pure silicon or perylene with isopentyl substituents is immobilized on a reduced GO monolayer despite the presence of perylene fluorescence peaks in the spectra. The surface-enhanced Raman scattering is caused by strong interactions between the unsubstituted chromophore and reduced GO due to aromatic stacking, which interactions provide efficient energy transfer between the components. The interactions between the substituted chromophore and the carbon framework are weak due to steric hindrances, being expressed in the absence of Raman scattering enhancement.

Recent Research and Development Status of Relaxed Optics and Laser Technology: A Review

It is shown that for laser technologies it was necessary to create a new branch of physics: Relaxed Optics (synthesis of methods of the physical optics, quantum electronics, physical chemistry, physics of irreversible phenomena in unitary system). It is allowed to explain complex chain processes of interaction light and matter. Possible applications of Relaxed Optical methods for the modeling of the laser-induced processes phenomena, including laser implantation (surface and subsurface processes), laser-induced optical breakdown (volume processes) and laser annealing of radiation and other defects in solid, are discussed. Perspectives of using these methods for the creation of new laser technologies, including creation new types of optoelectronic devices (heterostructures, diffraction lattices, etc.), resolution the problems of metallurgy, material science, painting, architecture and a building, are analyzed.

UV/Near-IR dual band photodetector based on p-GaN/α-In2Se3 heterojunction

In this report, we demonstrate dual band vertical heterojunction photodetector realized by integrating α-In2Se3 with p-type GaN. Flakes of ∼ 110 nm thickness were exfoliated on MOCVD grown p-GaN on silicon substrate. Devices showed two distinct detection peaks in spectral responsivity, one at 365 nm and another at 850 nm, corresponding to band edges of GaN and α-In2Se3 respectively, with considerable rejection in visible spectrum. Normalised responsivity values were found out to be ∼70 mA/W at both 365 nm and 850 nm for the bias of -3V along with photo-to-dark current ratio of ∼665 and ∼75 in that order. The Devices also showed fast transient response with no persistent photoconductivity (PPC). The specific detectivity values estimated were ∼1011 Jones and ∼1010 Jones corresponding to illumination at 365 nm and 850 nm, respectively. Device showed ∼0.4 dependence on incident power at 365 nm. The device performance, post annealing was also studied. This study is expected to pave the way for new type of optoelectronic devices by integrating direct bandgap layered material like α-In2Se3 and wide bandgap semiconductors.

Dynamics and efficient conversion of excitons to trions in non-uniformly strained monolayer WS2

We investigate the transport of excitons and trions in monolayer semiconductor WS$_2$ subjected to controlled non-uniform mechanical strain. We actively control and tune the strain profiles with an AFM-based setup in which the monolayer is indented by an AFM tip. Optical spectroscopy is used to reveal the dynamics of the excited carriers. The non-uniform strain configuration locally changes the valence and conduction bands of WS$_2$, giving rise to effective forces attracting excitons and trions towards the point of maximum strain underneath the AFM tip. We observe large changes in the photoluminescence spectra of WS$_2$ under strain, which we interpret using a drift-diffusion model. We show that the transport of neutral excitons, a process that was previously thought to be efficient in non-uniformly strained 2D semiconductors and termed as "funneling", is negligible at room temperature in contrast to previous observations. Conversely, we discover that redistribution of free carriers under non-uniform strain profiles leads to highly efficient conversion of excitons to trions. Conversion efficiency reaches $\simeq 100\%$ even without electrical gating. Our results explain inconsistencies in previous experiments and pave the way towards new types of optoelectronic devices.

Narrow Bandgap Pb–Sn Perovskites/InGaZnO Hybrid Phototransistors for Near‐Infrared Detection

Inorganic–organic hybrid perovskite thin films have attracted significant attention for developing new types of optoelectronic devices due to their superb optoelectronic properties. Herein, a hybrid phototransistor for near‐infrared (NIR) detection is constructed by capping a narrow bandgap Pb–Sn perovskite layer on top of an indium gallium zinc oxide (IGZO) thin‐film transistor (TFT), with a C60 interlayer acting as the electron transporting layer. The Pb–Sn perovskite layer is precisely spin patterned onto the IGZO TFTs' channel region via a hydrophobic perfluoro(1‐butenyl vinyl ether) (CYTOP) photolithography process. In this configuration, a high‐detectivity (2.24 × 1010 Jones at 900 nm) perovskite–C60–IGZO hybrid infrared phototransistor is achieved, and the narrow bandgap perovskite–IGZO hybrid phototransistor has a sensitive photoresponse down to 1100 nm.

An Etching‐Free Approach Toward Large‐Scale Light‐Emitting Metasurfaces

AbstractA new class of quasi 2D optical components, known as metasurfaces and exhibiting exceptional optical properties have emerged in recent years. The scattering properties of their subwavelength patterns allow molding the wavefront of light in almost any desired manner. While the proof of principle is demonstrated by various approaches, only a handful of low cost and fabrication friendly materials are suitable for practical implementations. To further develop this technology toward broadband application and industrial production, new materials and new fabrication methods are required. In addition, moving from passive to active devices with, for instance, dynamic tuning requires to move from dielectrics to semiconductors. Here, an etching‐free process is presented that combines nanoimprint and selective area sublimation of a semiconductor material to realize centimeter‐scale metalenses of high optical quality. Use of gallium nitride is chosen for this demonstration, as it is a widespread semiconductor which can be transparent and active in the visible. The sublimation leads to reduced surface roughness and defects compared to reactive ion etching. As a result, the devices show enhanced photoluminescence efficiency with respect to etched devices. Amplification due to gain in the semiconductor based metaoptics could lead to a new type of optoelectronic devices.

Assembling of Sulfur Quantum Dots in Fission of Sublimed Sulfur.

A novel kind of quantum dots, sulfur quantum dots (S dots), is synthesized by simply treating sublimated sulfur powders with alkali using polyethylene glycol-400 as passivation agents. The synthesized S dots exhibit excellent aqueous dispersibility, eminent photostability and temperature dependent photoluminescence (PL). An "assemble-fission" mechanism is proposed for the S dots formation in which "assembling" and "fission" are involved and contest each other. The ultimate morphologies of the S dots are dependent on the balance of the two forces. Guided by the assemble-fission mechanism, weakening the assembling effect is beneficial for obtaining monodisperse S dots, which can be achieved by pretreating of sulfur powder with nitric acid. PL wavelength of the S dots has been successfully tuned between green and blue light (from 550 to 440 nm) by simply controlling reaction time. A satisfactory quantum yield of 3.8% is obtained. Significant electrochemiluminescence of the S dots is observed in an annihilation reaction. Chemiluminescence from the S dots has been observed by direct oxidation. Taking advantage of unique and inherent antimicrobial activity of the sulfur particles, it is believed that this new emerging luminescent nanomaterial is highly promising in the development of new types of optoelectronic devices and tracer for live cells, in vivo imaging and diagnostics.

Controllable Laser Reduction of Graphene Oxide Films for Photoelectronic Applications.

This article presents a new simple method of creating light-absorbing carbon material for optical devices such as bolometers. A simple method of laser microstructuring of graphene oxide is used in order to create such material. The absorption values of more than 98% in the visible and more than 90% in the infrared range are achieved. Moreover thermal properties of the films, such as temperature dependence and the thermal response of the samples, are studied. The change in resistance with temperature is 13 Ohm K-1, temperature coefficient of resistance (TCR) is 0.3% K-1, and the sensitivity is 0.17 V W-1 at 300 K. Thermal conductivity is rather high at ∼104 W m-1 K-1 at 300 K. The designed bolometer operates at room temperature using incandescent lamp as a light source. This technique suggests a new inexpensive way to create a selective absorption coating and/or active layer for optical devices. Developed GO and rGO films have a large surface area and high conductivity. These properties make carbon coatings a perfect candidate for creating a new type of optoelectronic devices (gas sensors, detectors of biological objects, etc.).

Ultrathin niobium nanofilms on fiber optical tapers--a new route towards low-loss hybrid plasmonic modes.

Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10 nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper, and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3–4 dB/mm in aqueous environment and a refractive index sensitivity up to 15 μm/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous, and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices.

Optical Properties of ZnO Nanowires Decorated with Au Nanoparticles

One of the key technologies in future optoelectronics is control of excitons in oxide materials by the coupling with plasmons on noble metal surfaces. Optical properties of ZnO nanowires decorated with Au nanoparticles were studied to understand fundamental mechanism of the coupling and to develop optoelectronic devices with new functionalities. Light intensity at the main peak position in the photoluminescence (PL) spectra of ZnO nanowires was enhanced with the coverage of Au nanoparticles. Lifetime of excitons excited optically decreased by the decoration of Au nanoparticles. Understanding of the coupling between excitons and plasmons leads to optical control of excitons and will pave the way for new type of optoelectronic devices.

Nano Photoelectric Material Structures – Photonic Crystals

Photonic crystals are periodic dielectric structural materials that have photonic band gaps, and are divided into on-dimensional, two-dimensional, and three-dimensional structures based on their spatial distributions. One-dimensional photonic crystals have already found real-world applications. Three-dimensional photonic crystals are still in the experimental phase in laboratories. Due to their superior characteristics, photonic crystal materials are sure to be widely developed and applied in the future. This paper briefly introduces the principle of photonic crystals, facts about their theoretical research, production and preparation of materials, as well as their related applications. Photonic crystal materials have a lot of potential, and could be one of the most significant materials of this century. Since the concept was proposed in the late 80’s of the previous century, the research and application of photonic crystals has advanced significantly. Currently, photonic crystals are already used in fiber optics as well as semiconductor lasers. This paper introduces the structures of various types of photonic crystals, including photonic crystals with semiconductor and fiber optic material bases, and describes some of the special optoelectronic characteristics and possible applications of photonic crystals. Photonic crystals can be used in the production of many new types of optoelectronic devices. Most significantly, they can dramatically reduce the size of components and result in dense integration. Photonic crystals are expected to have a revolutionary impact on the development of optoelectronic technologies.

Electric-Field Switching of Bright and Dark Excitons in Semiconductor Crossed Nanowires

We investigate theoretically the exciton states in semiconductor crossed nanowires (CNWs) and it is found that the energy spectrum and electro-PL spectrum of the exciton in the CNWs can be tuned by the size of the nanowires using electric fields. An interesting bright-to-dark exciton transition can be found and it significantly affects the photoluminescence spectrum by the electric fields, which can be used to design new types of optoelectronic devices.

A study of plasmonics in metallic photonic quantum wires

The effect of plasmons on the bound photon modes has been studied in metallic photonic quantum nanowires. Nanowires are made from a metallic photonic crystal and a dielectric photonic crystal where the former is embedded into the latter. Photons are localized within the metallic crystal and are reflected from the dielectric crystal. The nanowire is doped with nanoparticles, which are interacting with the localized photons. It is found that number of bound photons states within the wire depends on the plasmon frequency. The bound photon energy decreases as the plasmon energy increases. Numerical simulations of the absorption coefficient predict that the position of a transparent state can be switched by changing the frequency of plasmons. The present study can be used to make new types of optoelectronic devices.