Optoelectric Devices Research Articles

Reaching medium entropy oxides with rocksalt structure based on cluster-plus-glue-atom model: A case study of Co-Ni-Cu-Zn-O system with tunable optoelectrical properties

Mg–Co–Ni–Cu–Zn–O is the firstly reported high entropy oxide (HEO) which has great promise in optoelectrical applications. However, the multicomponent and decreased configurational entropy by extracting one element from (Mg, Co, Ni, Cu, Zn) makes it difficult to synthesize single-phase medium entropy oxides (MEOs) especially when the cations are non-equimolar. In this paper, we synthesized different compositional-type of non-equimolar Co–Ni–Cu–Zn–O MEOs possessing single-phase rocksalt structure guided by the cluster-plus-glue-atom model. Interestingly, Co21Ni43Cu16Zn16O96 and Co17Ni47Cu16Zn16O96 have the lowest single-phase formation temperature (850 °C) when the total cation content is kept unchanged. Further increase or decrease of Co/Ni content (none, little, more) will increase the difficulty of single-phase formation ability and temperature (900–1200 °C). It is suggested the single-phase formation ability of Co–Ni–Cu–Zn–O MEOs is closely related to the Gibbs free energy (ΔG) and average cation-size difference (δ). The linear decrease of Co content and increase of Ni content can monotonously enlarge the energy band gap (Eg) from 1.52 eV to 1.93 eV and increase the electrical impedance with five orders of magnitude (∼103 Ω–∼108 Ω), which may be valuable in the fields of optoelectrical devices.

Compression-sensitive smart windows: inclined pores for dynamic transparency changes

Smart windows, capable of tailoring light transmission, can significantly reduce energy consumption in building services. While mechano-responsive windows activated by strains are promising candidates, they face long-lasting challenges in which the space for the light scatterer’s operation has to be enlarged along with the window size, undermining the practicality. Recent attempts to tackle this challenge inevitably generate side effects with compromised performance in light modulation. Here, we introduce a cuttlefish-inspired design to enable the closing and opening of pores within the 3D porous structure by through-thickness compression, offering opacity and transparency upon release and compression. By changing the activation mode from the conventional in-plane to through-thickness direction, the space requirement is intrinsically decoupled from the lateral size of the scatterer. Central to our design is the asymmetry of pore orientation in the 3D porous structure. These inclined pores against the normal direction increase the opaqueness upon release and improve light modulation sensitivity to compression, enabling transmittance regulation upon compression by an infinitesimal displacement of 50 μm. This work establishes a milestone for smart window technologies and will drive advancements in the development of opto-electric devices.

Synergetic Electrostatic and Steric Effects in α-FAPbI3 Single Crystals For X-Ray Detection and Imaging.

It is still challenging to stabilize α-FAPbI3 perovskite for high performance optoelectrical devices. Herein, a novel strategy is proposed utilizing the synergetic electrostatic and steric effect to stabilize the α-FAPbI3 phase and suppress the ion migration. Dimethylamine (DMA+) cations are chosen as the dopant to fabricate FA0.96DMA0.04PbI3 single crystals (SCs). DFT calculations reveal that DMA+ cations can improve the stability of α-FAPbI3 phase in both thermodynamics (lower Gibbs free energy) and kinetics (higher defect formation and migration energy). The resulting SCs exhibit an environmental stability over 100 days and an extraordinary low dark current drift of 3.7×10-7nAcm-1s-1V-1, comparable to 2D perovskite SCs. The X-ray detectors have also achieved the-state-of-the-art performance in X-ray detection and imaging. This work demonstrates the significance of electrostatic and steric effects in improving the phase and operational stability of perovskites.

Time-Resolved Mechanism of Positive Aging in InP Quantum-Dot Light-Emitting Diodes.

Positive aging has been reported to be effective for enhancing electroluminescence characteristics of quantum dot (QD) based optoelectrical devices. This study investigated the intricate mechanisms underlying the positive aging effect in quantum-dot light-emitting diodes (QLEDs) influenced by encapsulation with ultraviolet-curable resin. A 120-h analysis assessed the impact of the resin on the electron transport layer and emission layer, utilizing a strategically positioned perfluorinated ionomer (PFI) interlayer. The PFI layer effectively delayed the Al2O3 formation at the zinc magnesium oxide (ZMO)/Al interface and further reduced the interactions within the QD/ZMO interface, thereby curtailing exciton quenching at the interfaces. The time-sequential effect of positive aging demonstrated that resin encapsulation effectively passivates the ZMO surfaces after 12 h. The positive aging facilitated the reaction between aluminum and oxygen from ZMO, contributing to Al2O3 formation within 48 h of aging. Furthermore, positive aging passivated the defect states of the QD surface and the QD/ZMO interface, reducing exciton quenching at the QD or QD/ZMO interface. The enhanced electron injection and reduced exciton quenching resulted in aged InP QLEDs, exhibiting an external quantum efficiency of 12.04%. This is a significant increase from the 3.16% observed in the control device. Finally, a sequential mechanism of positive aging in InP QLEDs was devised, providing new insights into the time-related operation of aging agents. This study elucidates an advanced time-resolved mechanism of positive aging, thereby offering valuable insights into the intricate dynamics of excitons within the domain of QLED physics.

Triggering dual-mode dynamic optical responses by anchoring carbon dots on MnO2 hollow spheres

Multi-mode responsive optical materials with versatile application prospects for optical sensing, optoelectrical devices, and information encryption are highly desired. Here we integrate fluorescent carbon dots onto the hollow MnO2 spheres, and modulate the interaction between them to achieve a water-stimulated responsive system with dual-mode dynamic signals in both fluorescence and structural color. The composite film shows a structural color shifting from blue to green as well as displays a fluorescence “on” in the presence of trace water, with both changes capable of being reversibly switched up to 10 times. The amide bond between the two components enables the controllable dispersion and aggregation of the carbon dots which is essential to the reversibility. Fabrication of several security labels with separate information in structural color and fluorescence channels demonstrates the application potential of the composite. This work provides a concise route to develop new multi-mode responsive optical materials for applications in anti-counterfeiting, sensing, and coding.

Quantum Dot-Based Three-Stack Tandem Near-Infrared-to-Visible Optoelectric Upconversion Devices.

Quantum dots (QDs) exhibit size-tunable optical properties, making them suitable for efficient light-sensing and light-emitting devices. Tandem devices that can convert near-infrared (NIR) to visible (Vis) signals can be fabricated by integrating an NIR-sensing QD device with a Vis electroluminescence (EL) QD device. However, these devices require delicate control of the QD layer during processing to prevent damage to the predeposited QD layers in tandem devices during the subsequent deposition of other functional layers. This has restricted attainable device structures for QD-based upconversion devices. Herein, we present a modular approach for fabricating QD-based optoelectric upconversion devices. This approach involves using NIR QD-absorbing (Abs) and Vis QD-EL units as building modules, both of which feature cross-linked functional layers that exhibit structural tolerance to dissolution during subsequent solution-based processes. Tandem devices are fabricated in both normal (EL unit on Abs unit) and inverted (Abs unit on EL unit) structures using the same set of NIR QD-Abs and Vis QD-EL units stacked in opposite sequences. The tandem device in the normal structure exhibits a high NIR photon-to-Vis-photon conversion efficiency of up to 1.9% in a practical transmissive mode. By extending our modular approach, we also demonstrate a three-stack tandem device that incorporates a single NIR-absorbing unit coupled with two EL units, achieving an even higher conversion efficiency of up to 3.2%.

The amplification effect of four-phonon scattering in CdX (X=Se, Te): The role of mid-frequency phonons

Recently, CdX (X = Se, Te) materials have garnered notable interest owing to their great application potential for high-efficiency solar cells, fiber optic communication systems, and nanoelectronic devices. The performance of optoelectric devices is significantly influenced by the thermal conductivity. In this study, a combination of machine-learning methods and first-principles calculations is utilized to investigate the phonon thermal transport properties of CdSe and CdTe, as well as to give deep insights into the phonon behavior in heat transfer. It is found that acoustic phonons dominate the lattice thermal conductivity (κ) in CdSe, while optical phonons contribute around 50 % to the κ value in CdTe. There are strikingly strong four-phonon scattering phenomena in both materials, which result in 55 % and 66 % reduction in κ values for CdSe and CdTe, respectively. Further analysis shows that the mid-frequency phonons play an important role in amplifying the four-phonon scattering. Its special frequency positions permit an unusually large number of four-phonon scattering processes to occur and cause large scattering of low-frequency phonons. This mechanism differs from earlier proposed features regarding large acoustic-optical gaps, bunching of acoustic branches and four-phonon Fermi resonance, which implies strong four-phonon anharmonicity. Thus, the present work opens up new prospects in the exploration and design of innovative thermoelectric material, which provides a more thorough understanding of the four-phonon scattering mechanisms in crystalline solids.

Doped SnO2 thin films fabricated at low temperature by atomic layer deposition with a precise incorporation of niobium atoms

Nb-doped SnO2 (NTO) thin films were synthesized by atomic layer deposition technique at low temperature (100 °C). For an efficient incorporation of the Nb atoms, i.e. fine control of their amount and distribution, various supercycle ratios and precursor pulse sequences were explored. The thin film growth process studied by in-situ QCM revealed that the Nb incorporation is highly impacted by the surface nature as well as the amount of species available at the surface. This was confirmed by the actual concentration of the Nb atom incorporated inside the thin film as determined by XPS. Highly transparent thin films which transmit more than 95% of the AM1.5 global solar irradiance over a wide spectral range (300–1000 nm) were obtained. In addition, the Nb atoms influenced the optical band gap, conduction band, and valence band levels. While SnO2 thin film were too resistive, films tuned to conductive nature upon Nb incorporation with controlled concentration. Optimal incorporation level was found to be ⩽1 at.% of Nb, and carrier concentration reached up 2.5 × 1018 cm−3 for the as-deposited thin films. As a result, the high optical transparency accompanied with tuned electrical property of NTO thin films fabricated by ALD at low temperature paves the way for their integration into temperature-sensitive, nanostructured optoelectrical devices.

The draft genome of Nitzschia closterium f. minutissima and transcriptome analysis reveals novel insights into diatom biosilicification

BackgroundNitzschia closterium f. minutissima is a commonly available diatom that plays important roles in marine aquaculture. It was originally classified as Nitzschia (Bacillariaceae, Bacillariophyta) but is currently regarded as a heterotypic synonym of Phaeodactylum tricornutum. The aim of this study was to obtain the draft genome of the marine microalga N. closterium f. minutissima to understand its phylogenetic placement and evolutionary specialization. Given that the ornate hierarchical silicified cell walls (frustules) of diatoms have immense applications in nanotechnology for biomedical fields, biosensors and optoelectric devices, transcriptomic data were generated by using reference genome-based read mapping to identify significantly differentially expressed genes and elucidate the molecular processes involved in diatom biosilicification.ResultsIn this study, we generated 13.81 Gb of pass reads from the PromethION sequencer. The draft genome of N. closterium f. minutissima has a total length of 29.28 Mb, and contains 28 contigs with an N50 value of 1.23 Mb. The GC content was 48.55%, and approximately 18.36% of the genome assembly contained repeat sequences. Gene annotation revealed 9,132 protein-coding genes. The results of comparative genomic analysis showed that N. closterium f. minutissima was clustered as a sister lineage of Phaeodactylum tricornutum and the divergence time between them was estimated to be approximately 17.2 million years ago (Mya). CAFF analysis demonstrated that 220 gene families that significantly changed were unique to N. closterium f. minutissima and that 154 were specific to P. tricornutum, moreover, only 26 gene families overlapped between these two species. A total of 818 DEGs in response to silicon were identified in N. closterium f. minutissima through RNA sequencing, these genes are involved in various molecular processes such as transcription regulator activity. Several genes encoding proteins, including silicon transporters, heat shock factors, methyltransferases, ankyrin repeat domains, cGMP-mediated signaling pathways-related proteins, cytoskeleton-associated proteins, polyamines, glycoproteins and saturated fatty acids may contribute to the formation of frustules in N. closterium f. minutissima.ConclusionsHere, we described a draft genome of N. closterium f. minutissima and compared it with those of eight other diatoms, which provided new insight into its evolutionary features. Transcriptome analysis to identify DEGs in response to silicon will help to elucidate the underlying molecular mechanism of diatom biosilicification in N. closterium f. minutissima.

Enhanced photovoltaic response in WSe2 photodetector with asymmetric two-dimensional contacts

Asymmetric contact pairs with different work functions provide an efficient method to extract photogenerated carriers in optoelectrical devices. Specifically, vertical optoelectrical devices based on two-dimensional (2D) materials utilize graphene layers as the bottom and top contacts. Whereas an additional terminal is required for electrostatic doping in either top or bottom graphene to enlarge the built-in electric field. Herein, we present an enhanced photovoltaic response in a vertical WSe2 photodetector utilizing asymmetric 2D contacts. A graphite layer and a degenerate SnSe2 are used as the top and bottom contacts, respectively, with a significant difference in their work functions. By establishing a large built-in electric field across the vertical WSe2 layer, a strong photovoltaic effect is achieved, resulting in an open-circuit voltage of 0.37 V and a short-circuit current of 0.42 μA under 532 nm illumination. The device shows high-performance photodetection characteristics, with a responsivity of 32.04 A W−1, external quantum efficiency of 7475%, and specific detectivity of 3.61 × 1012 Jones. Furthermore, the device can generate a maximum output electrical power of 70.9 nW, enabling a high-power conversion efficiency of 3.5%.

Interface optoelectrical dynamic in 2D perovskite/InSe heterostructure

Van der Waals (vdW) heterostructure composed of two-dimensional (2D) materials and 2D perovskite has shown excellent optoelectrical properties recently, while the interfacial coupling is less investigated. Here, van der Waals InSe/(C4H9NH3)2(CH3NH3)Pb2I7 heterostructure is fabricated and systemically investigated by photoluminescence (PL) spectroscopy. An optical broadband emission is generated due to the formation of heterostructure. The first principle calculation and variable PL spectra suggest the dynamic generation of defects such as iodine vacancy and charge states. Electron–phonon coupling of the 2D perovskite is weakened from −127 meV to −90 meV in the heterostructure. The band offset causes the built-in electrical field, which strengthens the optoelectrical response of heterostructure devices. The results deepen the understanding of the interfacial optoelectrical dynamic of 2D perovskite-related vdW heterostructure and help develop superior optoelectrical vdW heterostructure devices.

Excitons, optical spectra, and electronic properties of semiconducting Hf-based MXenes.

Semiconducting MXenes are an intriguing two-dimensional (2D) material class with promising electronic and optoelectronic properties. Here, we focused on recently prepared Hf-based MXenes, namely, Hf3C2O2 and Hf2CO2. Using the first-principles calculation and excited state corrections, we proved their dynamical stability, reconciled their semiconducting behavior, and obtained fundamental gaps by using the many-body GW method (indirect 1.1 and 2.2eV; direct 1.4 and 3.5eV). Using the Bethe-Salpeter equation, we subsequently provided optical gaps (0.9 and 2.7eV, respectively), exciton binding energies, absorption spectra, and other properties of excitons in both Hf-based MXenes. The indirect character of both 2D materials further allowed for a significant decrease of excitation energies by considering indirect excitons with exciton momentum along the Γ-M path in the Brillouin zone. The first bright excitons are strongly delocalized in real space while contributed by only a limited number of electron-hole pairs around the M point in the k-space from the valence and conduction band. A diverse range of excitonic states in Hf3C2O2 MXene lead to a 4% and 13% absorptance for the first and second peaks in the infrared region of absorption spectra, respectively. In contrast, a prominent 28% absorptance peak in the visible region appears in Hf2CO2 MXene. Results from radiative lifetime calculations indicate the promising potential of these materials in optoelectric devices requiring sustained and efficient exciton behavior.

Light-Controlled Multiconfigurational Conductance Switching in a Single 1D Metal-Organic Wire.

Precise control of multiple spin states on the atomic scale presents a promising avenue for designing and realizing magnetic switches. Despite substantial progress in recent decades, the challenge of achieving control over multiconfigurational reversible switches in low-dimensional nanostructures persists. Our work demonstrates multiple, fully reversible plasmon-driven spin-crossover switches in a single π-d metal-organic chain suspended between two electrodes. The plasmonic nanocavity stimulated by external visible light allows for reversible spin crossover between low- and high-spin states of different cobalt centers within the chain. We show that the distinct spin configurations remain stable for minutes under cryogenic conditions and can be nonperturbatively detected by conductance measurements. This multiconfigurational plasmon-driven spin-crossover demonstration extends the available toolset for designing optoelectrical molecular devices based on SCO compounds.

High-performance e-beam-deposited (Sn2Sb2S5)GO:FTO supercapacitor electrode and photocatalytic thinfilm for contaminants removal

The present work outlines the synthesis of e-beam deposited (Sn2Sb2S5)GO:FTO thin film. The surface and physicochemical characterization of the thinfilm was done through X-ray diffraction (XRD), X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray and UV-visible spectrophotometry. An orthorhombic phased Sn2Sb2S5-GO was confirmed by XRD with crystallite size of 16.9 nm. SEM morphology revealed homogenous distribution of grains and sheet-like structure of graphene oxide (GO) and a direct band gap of 2.9 eV. Moreover, electrical investigation presented (Sn2Sb2S5)GO:FTO as an excellent electrode material with 303 F g−1 specific capacitance. The photocatalytic degradation rates by the thinfilm for methyl red dye, pesticide and phenol were 70%, 94% and 54%. The dynamic properties of the investigated film present it as a propitious material for opto-electrical and remediation devices.

Synthesis and comparative study of high Tg and colorless polyamide‐imides with different amide‐to‐imide ratio

AbstractColorless polyimide (CPI), a heat‐resistant polymer being widely used in optoelectrical devices, has attracted worldwide attention. Polyamide‐imides due to the incorporation of amide groups into the CPI chains enhance the polymer performance by improving the thermal dimensional stability and excellent mechanical properties without sacrificing the optical transparency. In this article, CPI films PI‐(1‐3) are synthesized from one‐step polymerization of 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and cyclopentanone bis‐spironorbornane tetracarboxylic dianhydride (CpODA) with amide‐containing diamine N,N′‐(2,2′‐bis(trifluoromethyl)‐[1,1′‐biphenyl]‐4,4′‐diyl)bis(4‐aminobenzamide) (AB‐TFDB) and bis(trifluoromethyl)benzidine (TFDB). In comparison, by adjusting the ratio of imide and amide groups in the repeating unit, PI‐(4‐5) are prepared from copolymerization of terephthaloyl chloride (TPC), 6FDA, and CpODA with TFDB diamine. PI‐(1‐5) with 90% transmittance in the visible region tailored the excellent thermal and mechanical properties. Particularly, PI‐3 exhibited a high glass transition temperature of 412°C, a coefficient of thermal expansion of 20.8 ppm/K, a tensile strength of 128 MPa, and an elastic modulus of 5.4 GPa. The results also concluded that irrespective of the polyamide‐imide synthesis strategy, CPI films with similar amide‐to‐imide ratio in polymer chain demonstrated comparable optical, thermal, and mechanical properties.

Optical activation of implanted lanthanoid ions in aluminum nitride semiconductors by high temperature annealing

Lanthanoid (Ln)-doped aluminum nitride (AlN) semiconductors are one candidate for optoelectric devices and single photon sources, although their optical properties are less understood. We clarify the room temperature optical properties of Ln ion implanted single crystal AlN semiconductors and their changes upon thermal annealing by up to 1700 °C. Photoluminescence (PL), cathodoluminescence (CL), and time-resolved PL for praseodymium (Pr), europium (Eu), and neodymium (Nd) ion implanted AlN are analyzed. Recovery of implantation induced damages and thermal diffusion of implanted Ln ions by thermal annealing are also investigated. Our systematic studies reveal that there is a trade-off between optical activation of implanted Ln ions due to recovery of implantation damage and deactivation (quenching) due to complex formation and aggregation of Ln ions. The PL intensity of implanted Pr ions increases with increasing annealing temperature in the case of high-dose implantation (above 1020 cm-3), whereas it rather decreases in the case of low-dose implantation (below 4 × 1019 cm-3). However, the PL intensity is significantly reduced after annealing at 1700 °C in both cases, indicating that the quenching factor is dominant in this temperature range.

Development of biopolymer composite films based on chicory extract reinforced polyvinyl alcohol/chitosan blend via green approach for flexible optoelectrical devices

AbstractBiopolymer blend composite films based on polyvinyl alcohol (PVA) and chitosan (CS) incorporated with varying amounts of chicory extract (CE) have been developed by the green solution casting technique. The impact of CE content on structural, thermal, mechanical and electrical properties was thoroughly examined. The existence of intermolecular interactions in the blend composite was confirmed by Fourier‐transform infrared and ultraviolet spectroscopy. The x‐ray diffraction pattern proved the successful preparation of PVA/CS/CE composite film. The scanning electron microscopy images of the composites showed shape and grain size for the different bio‐filler contents. The thermal transition temperature of the blend composites was significantly improved by the addition of CE extract deduced from differential scanning calorimetry. The dielectric study showed that the permittivity remarkably increases with decreasing frequency and maximum dielectric constant was observed for 15 wt% loading. The activation energy obtained from the AC conductivity decreased as the temperature increased. The addition of CE extract improved the hardness and tensile strength of the PVA/CS blend composite in comparison with a pristine pure blend. The controllable mechanical, thermal, optical, and electrical characteristics of the PVA/CS blend composite suggest that it might be an attractive optical material for the advancement of futuristic flexible‐type optoelectronic and energy storage systems.

BF3‐induced reversible covalent organic framework radicals

AbstractThe integration of radials into covalent organic frameworks (COFs) would have a profound effect on their applications in spin devices since such radical arrays can offer scientists an additional dimension to manipulate electron spins and maximize the function of organic optoelectrical devices. However, such realization (especially reversible radicals) is very challenging. In this article, using a fluorene‐based benzoquinone‐derived monomer (M) as the building unit, we successfully synthesized a boroxine‐linked COF (named CityU‐3), whose crystallinity and chemical composition were confirmed by powder X‐ray diffraction (PXRD), Fourier‐transform infrared (FT‐IR) spectroscopy, solid‐state 13C cross‐polarization magic‐angle‐spinning (CP/MAS) NMR, and X‐ray photoelectron spectroscopy (XPS). Interestingly, CityU‐3 can be converted into its radical form by treating with BF3·Et2O, which is associated with a color change from red to black, and vice versa upon heating. The as‐formed radicals have been confirmed by electron paramagnetic resonance (EPR) spectroscopy. It is worth pointing out that the cycles between radical formation and disappearance would not affect its crystallinity and structure. The reversible COF radicals would have great applications in organic spin devices.

Effect of thickness on the electrical properties of PEDOT:PSS/Tween 80 films

The lower material and manufacturing costs of conductive polymers, particularly PEDOT:PSS, compared to indium tin oxide have led to significant research into their use in optoelectric devices. In this study, improvements of the electrical properties of PEDOT:PSS and PEDOT:PSS/Tween 80 via the production of multilayered films were investigated. A single layer of pristine PEDOT:PSS was found to give a sheet resistance of 1639 Ω□–1. The application of an additional three layers reduced this value to 29 Ω□-1, corresponding to an increase in conductivity from 2.6 to 18.3 Scm–1. A similar trend was also found with formulations containing Tween 80. X-ray diffraction and Raman spectroscopy showed that the additional layers increased the crystalline order and induced a slight benzoid to quinoid shift. Surface profiling showed progressive increases in surface roughness with each additional layer of pristine PEDOT:PSS; however, this was mitigated by the presence of Tween 80 in the formulations.

High-performance amplified spontaneous emission in inorganic CsPbBr3 perovskite thin films grown on engineered quartz substrates.

In this work, periodic rectangular arrays were fabricated on quartz substrates using the femtosecond laser ablation technique, on which inorganic cesium lead bromide thin films were grown using the spin coating method. Enhanced photoluminescence emission was investigated using a homebuilt confocal microscope, and increased light absorption due to the engineered structures was also measured. High-performance amplified spontaneous emission with typical narrow lasing emission peaks excited using a nanosecond laser centered at 266 nm was obtained. This work provides a method to modify the performance of optoelectrical devices, which helps develop light-emitting diodes, photodetectors, solar cells, and lasers.