A simple encapsulation method for organic optoelectronic devices

The performances of organic optoelectronic devices, such as organic light emitting diodes and polymer solar cells, have rapidly improved in the past decade. The stability of an organic optoelectronic device has become a key problem for further development. In this paper, we report one simple encapsulation method for organic optoelectronic devices with a parafilm, based on ternary polymer solar cells （PSCs）. The power conversion efficiencies （PCE） of PSCs with and without encapsulation decrease from 2.93% to 2.17% and from 2.87% to 1.16% after 168-hours of degradation under an ambient environment, respectively. The stability of PSCs could be enhanced by encapsulation with a parafilm. The encapsulation method is a competitive choice for organic optoelectronic devices, owing to its low cost and compatibility with flexible devices.

New Optoelectronic Devices and Technologies for RoF

In the high-frequency microwave photonics field,Radio over Fiber (RoF) technology has become a hot topic in the development of next generation broadband wireless communication technologies.In recent years,based on new optoelectronic devices that support RoF technology,several optical generation and receiving techniques of millimeter-wave subcarriers have been developed,including external modulation,radio frequency up-conversion,heterodyning and millimeter-wave modulated optical pulse generator.The development of these technologies will no doubt quicken the pace of commercialization of RoF technology.

Single-molecule optoelectronic devices:physical mechanism and beyond

Single-molecule devices not only promise to provide an alternative strategy to break through the miniaturization and functionalization bottlenecks faced by traditional semiconductor devices,but also provide a reliable platform for exploration of the intrinsic properties of matters at the single-molecule level.Because the regulation of the electrical properties of single-molecule devices will be a key factor in enabling further advances in the development of molecular electronics,it is necessary to clarify the interactions between the charge transport occurring in the device and the external fields,particularly the optical field.This review mainly introduces the optoelectronic effects that are involved in single-molecule devices,including photoisomerization switching,photoconductance,plasmon-induced excitation,photovoltaic effect,and electroluminescence.We also summarize the optoelectronic mechanisms of single-molecule devices,with particular emphasis on the photoisomerization,photoexcitation,and photo-assisted tunneling processes.Finally,we focus the discussion on the opportunities and challenges arising in the single-molecule optoelectronics field and propose further possible breakthroughs.

Graphene applications in electronic and optoelectronic devices and circuits

Recent progress of research for graphene applications in electronic and optoelectronic devices is reviewed, and recent developments in circuits based on graphene devices are summarized. The bandgap-mobility tradeoff inevitably constrains the application of graphene for the conventional field-effect transistor （FET） devices in digital applications. However, this shortcoming has not dampened the enthusiasm of the research community toward graphene electronics. Aside from high mobility, graphene offers numerous other amazing electrical, optical, thermal, and mechanical properties that continually motivate innovations.

Flexible nanoimprint lithography enables high-throughput manufacturing of bioinspired microstructures on warped substrates for efficient III-nitride optoelectronic devices

III-nitride materials are of great importance in the development of modern optoelectronics,but they have been limited over years by low light utilization rate and high dislocation densities in heteroepitaxial films grown on foreign substrate with limited refractive index contrast and large lattice mismatches.Here,we demonstrate a paradigm of high-throughput manufacturing bioinspired microstructures on warped substrates by flexible nanoimprint lithography for promoting the light extraction capability.We design a flexible nanoimprinting mold of copolymer and a two-step etching process that enable high-efficiency fabrication of nanoimprinted compound-eye-like Al2O3 microstructure(NCAM)and nanoimprinted compound-eye-like SiO_(2)microstructure(NCSM)template,achieving a 6.4-fold increase in throughput and 25%savings in economic costs over stepper projection lithography.Compared to NCAM template,we find that the NCSM template can not only improve the light extraction capability,but also modulate the morphology of AlN nucleation layer and reduce the formation of misoriented GaN grains on the inclined sidewall of microstructures,which suppresses the dislocations generated during coalescence,resulting in 40%reduction in dislocation density.This study provides a low-cost,high-quality,and high-throughput solution for manufacturing microstructures on warped surfaces of III-nitride optoelectronic devices.

Surface charge transfer doping for two-dimensional semiconductor-based electronic and optoelectronic devices

Doping of semiconductors,i.e.,accurately modulating the charge carrier type and concentration in a controllable manner,is a key technology foundation for modern electronics and optoelectronics.However,the conventional doping technologies widely utilized in silicon industry,such as ion implantation and thermal diffusion,always fail when applied to two-dimensional(2D)materials with atomically-thin nature.Surface charge transfer doping(SCTD)is emerging as an effective and non-destructive doping technique to provide reliable doping capability for 2D materials,in particular 2D semiconductors.Herein,we summarize the recent advances and developments on the SCTD of 2D semiconductors and its application in electronic and optoelectronic devices.The underlying mechanism of STCD processes on 2D semiconductors is briefly introduced.Its impact on tuning the fundamental properties of various 2D systems is highlighted.We particularly emphasize on the SCTD-enabled high-performance 2D functional devices.Finally,the challenges and opportunities for the future development of SCTD are discussed.

Flexible optoelectronic devices based on metal halide perovskites

The unique physical and chemical properties of metal halide perovskites predestine the devices to achieve high performance in optoelectronic field.Among the numerous high qualities of perovskites,their different low-temperature synthesis methods and preparation processes make them impressive and popular materials for flexible optoelectronic devices.Mainstream perovskite devices,for instance,solar cells,photodetectors and light-emitting diodes,have been fabricated on flexible substrates and show outstanding flexibility as well as high performance.For soft wearable electronic systems,mechanical flexibility is the premier condition.Compared to common devices based on rigid substrates,flexible perovskite devices are more practical and see widespread applications in energy,detection,display,and other fields.This review summarizes the recent progress of flexible perovskite solar cells,photodetectors and light-emitting diodes.The design and fabrication of different high-performance flexible perovskite devices are introduced.Various low-dimensional perovskite materials and configurations for flexible perovskite devices are presented.In addition,the limitations and challenges for further application are also briefly discussed.

A cost-effective 100-Gb/s transmitter with low-speed optoelectronic devices and high spectral efficiency

A 100-Gb/s high-speed optical transmitter is proposed and experimentally demonstrated. Based on frequency-quadrupling technique, two sub-channels with a fixed 50-GHz spacing are obtained from one laser source. Using return-to-zero differential quadrature phase-shift keying （RZ-DQPSK） modulation format and polarization multiplexing （PolMux）, only low-speed electronic devices of 12.5 GHz are needed for the 100-Gb/s transmitter. This eliminates the need of ultrahigh-speed optoelectronic devices and thus greatly reduces the cost. The experimental results show that this transmitter can achieve good performance in dispersion tolerance of a 25-km single mode fiber （SMF）.

p-/n-Type modulation of 2D transition metal dichalcogenides for electronic and optoelectronic devices

Two-dimensional layered transition metal dichalcogenides(TMDCs)have demonstrated a huge potential in the broad fields of optoelectronic devices,logic electronics,electronic integration,as well as neural networks.To take full advantage of TMDC characteristics and efficiently design the device structures,one of the most key processes is to control their p-/n-type modulation.In this review,we summarize the p-/n-type modulation of TMDCs based on diverse strategies consisting of intrinsic defect tailoring,substitutional doping,surface charge transfer,chemical intercalation,electrostatic modulation,and dielectric interface engineering.The modulation mechanisms and comparisons of these strategies are analyzed together with a discussion of their corresponding device applications in electronics and optoelectronics.Finally,challenges and outlooks for p-/n-type modulation of TMDCs are presented to provide references for future studies.

Recent progress in optoelectronic neuromorphic devices

Rapid developments in artificial intelligence trigger demands for perception and learning of external environments through visual perception systems.Neuromorphic devices and integrated system with photosensing and response functions can be constructed to mimic complex biological visual sensing behaviors.Here,recent progresses on optoelectronic neuromorphic memristors and optoelectronic neuromorphic transistors are briefly reviewed.A variety of visual synaptic functions stimulated on optoelectronic neuromorphic devices are discussed,including light-triggered short-term plasticities,long-term plasticities,and neural facilitation.These optoelectronic neuromorphic devices can also mimic human visual perception,information processing,and cognition.The optoelectronic neuromorphic devices that simulate biological visual perception functions will have potential application prospects in areas such as bionic neurological optoelectronic systems and intelligent robots.

Controllable growth and flexible optoelectronic devices of regularly-assembled Bi2S3 semiconductor nanowire bifurcated junctions and crosslinked networks

Regularly assembled structures of nanowires, such as aligned arrays, junctions and interconnected networks, have great potential for the applications in logical circuits, address decoders, photoelectronic devices and transparent electrodes. However, for now it is still lack of effective approaches for constructing nanowire bifurcated junctions and crosslinked networks with ordered orientations and high quality. Herein, we report the controlled growth of Bi2S3 semiconductor nanowire bifurcated junctions and crosslinked networks with well-aligned directions and high crystalline degree by utilizing the proportional lattice match between nanowires and substrates. Taking advantages of the “tip-to-stem splice” assembly of individual nanowires, the precise orientation alignments of Bi2S3 semiconductor nanowire bifurcated junctions and crosslinked networks were successfully realized. The controlled growth mechanism and structural evolution process have been elucidated by detailed atomic structure characterizations and modeling. The highly crystal quality and direct energy bandgap of as-assembled photodetectors based on individual bismuth sulfide nanowires enabled high photoresponsivity and fast switch time under light illumination. The three-terminal devices based on nanowire bifurcated junctions present rapid carrier transport across the junction. The flexible photodetectors based on nanowire crosslinked networks show very minimal decay of photocurrent after long-term bending test. This work may provide new insights for the guided construction and regular assembly of low-dimensional ordered functional nanostructures towards advanced nanotechnologies.

Two-dimensional optoelectronic devices for silicon photonic integration

With the unprecedented increasing demand for extremely fast processing speed and huge data capacity,traditional silicon-based information technology is becoming saturated due to the encountered bottle-necks of Moore's Law.New material systems and new device architectures are considered promising strategies for this challenge.Two-dimensional(2D)materials are layered materials and garnered persistent attention in recent years owing to their advantages in ultrathin body,strong light-matter interaction,flexible integration,and ultrabroad operation wavelength range.To this end,the integra-tion of 2D materials into silicon-based platforms opens a new path for silicon photonic integration.In this work,a comprehensive review is given of the recent signs of progress related to 2D material inte-grated optoelectronic devices and their potential applications in silicon photonics.Firstly,the basic op-tical properties of 2D materials and heterostructures are summarized in the first part.Then,the state-of-the-art three typical 2D optoelectronic devices for silicon photonic applications are reviewed in detail.Finally,the perspective and challenges for the aim of 3D monolithic heterogeneous integration of these 2D optoelectronic devices are discussed.

Recent advances in flexible and wearable organic optoelectronic devices

Flexible and wearable optoelectronic devices have been developing to a new stage due to their unique capacity for the possibility of a variety of wearable intelligent electronics, including bendable smartphones, foldable touch screens and antennas, paper-like displays, and curved and flexible solid-state lighting devices. Before extensive commercial applications, some issues still have to be solved for flexible and wearable optoelectronic devices. In this regard, this review concludes the newly emerging flexible substrate materials, transparent conductive electrodes, device architectures and light manipulation methods. Examples of these components applied for various kinds of devices are also summarized. Finally, perspectives about the bright future of flexible and wearable electronic devices are proposed.

First-principles calculations of nitrogen-doped antimony triselenide： A prospective material for solar cells and infrared optoelectronic devices

This study is focused on calculation of the electronic structure and optical properties of non-metal doped Sb2Se3 using the first-principles method. One and two N atoms are introduced to Sb and Se sites in a Sb2Se3 crystal. When one and two N atoms are introduced into the Sb2Se3 lattice at Sb sites, the electronic structure shows that the doping significantly modifies the bandgap of Sb2Se3 from 1.11 eV to 0.787 and 0.685 eV, respectively. When N atoms are introduced to Se sites, the material shows a metallic behavior. The static dielectric constants el（0） for Sb16Se24, SblsN1Se24, Sb14N2Se24, Sb16Se23N1, and Sb16Se22N2 are 14.84, 15.54, 15.02, 18.9, and 39.29, respectively. The calculated values of the refractive index n（0） for Sb16Se24, SblsN1Se24, Sb14N2Se24, Sb16Se23N1, and Sb16Se22N2 are 3.83, 3.92, 3.86, 4.33, and 6.21, respectively. The optical absorbance and optical conductivity curves of the crystal for N-doping at Sb sites show a significant redshift towards the short-wave infrared spectral region as compared to N-doping at Se sites. The modulation of the static refractive index and static dielectric constant is mainly dependent on the doping level. The optical properties and bandgap narrowing effect suggest that the N-doped Sb2Se3is a promising new semiconductor and can be a replacement for GaSb due to its very similar bandgap and low cost.

Fabrication of stable organometallic halide perovskite NWs based optoelectronic devices

Organometallic halide perovskite materials have triggered global attention in recent years due to their exciting and optimistic high performance energy conversion properties(high luminescence efficiency and tremendous optical absorption ability[1,2]).These interesting photovoltaic properties together make them a promising candidate for high performance optoelectronic

Optoelectronic devices based on two-dimensional transition metal dichalcogenides

In the past few years, two-dimensional （2D） transition metal dichalcogenide （TMDC） materials have attracted increasing attention of the research community, owing to their unique electronic and optical properties, ranging from the valley-spin coupling to the indirect-to-direct bandgap transition when scaling the materials from multi-layer to monolayer. These properties are appealing for the development of novel electronic and optoelectronic devices with important applications in the broad fields of communication, computation, and healthcare. One of the key features of the TMDC family is the indirect-to-direct bandgap transition that occurs when the material thickness decreases from multilayer to monolayer, which is favorable for many photonic applications. TMDCs have also demonstrated unprecedented flexibility and versatility for constructing a wide range of heterostructures with atomic-level control over their layer thickness that is also free of lattice mismatch issues. As a result, layered TMDCs in combination with other 2D materials have the potential for realizing novel high-performance optoelectronic devices over a broad operating spectral range. In this article, we review the recent progress in the synthesis of 2D TMDCs and optoelectronic devices research. We also discuss the challenges facing the scalable applications of the family of 2D materials and provide our perspective on the opportunities offered by these materials for future generations of nanophotonics technology.

Silicon-based optoelectronic synaptic devices

High-performance neuromorphic computing(i.e.,brain-like computing)is envisioned to seriously demand optoelectronically integrated artificial neural networks(ANNs)in the future.Optoelectronic synaptic devices are critical building blocks for optoelectronically integrated ANNs.For the large-scale deployment of high-performance neuromorphic computing in the future,it would be advantageous to fabricate optoelectronic synaptic devices by using advanced silicon(Si)technologies.This calls for the development of Si-based optoelectronic synaptic devices.In this work we review the use of Si materials to make optoelectronic synaptic devices,which have either two-terminal or three-terminal structures.A series of important synaptic functionalities have been well mimicked by using these Si-based optoelectronic synaptic devices.We also present the outlook of using Si materials for optoelectronic synaptic devices.

CuPc/C_(60) heterojunction thin film optoelectronic devices

The optoelectronic properties of heterojunction thin film devices with ITO/CuPc/C_（60）/Al structure have been investigated by analyzing their current-voltage characteristics,optical absorption and photocurrent.In this organic photovoltaic device,CuPc acts as an optically active layer,C_（60） as an electron-transporting layer and ITO and Al as electrodes.It is observed that,under illumination,excitons are formed,which subsequently drift towards the interface with C_（60）,where an internal electric field is present.The excitons that reach the interface are subsequently dissociated into free charge carriers due to the electric field present at the interface.The experimental results show that in this device the total current density is a function of injected carriers at the electrode-organic semiconductor surface,the leakage current through the organic layer and collected photogenerated current that results from the effective dissociation of excitons.

Low-Dimensional Halide Perovskites and Their Advanced Optoelectronic Applications

Metal halide perovskites are crystalline materials originally developed out of scientific curiosity. They have shown great potential as active materials in optoelectronic applications. In the last 6 years, their certified photovoltaic efficiencies have reached 22.1%. Compared to bulk halide perovskites, low-dimensional ones exhibited novel physical properties. The photoluminescence quantum yields of perovskite quantum dots are close to 100%. The external quantum efficiencies and current efficiencies of perovskite quantum dot light-emitting diodes have reached 8% and 43 cd A^(-1),respectively, and their nanowire lasers show ultralow-threshold room-temperature lasing with emission tunability and ease of synthesis. Perovskite nanowire photodetectors reached a responsivity of 10 A W^(-1)and a specific normalized detectivity of the order of 10^(12 )Jones. Different from most reported reviews focusing on photovoltaic applications, we summarize the rapid progress in the study of low-dimensional perovskite materials, as well as their promising applications in optoelectronic devices. In particular, we review the wide tunability of fabrication methods and the state-of-the-art research outputs of low-dimensional perovskite optoelectronic devices. Finally, the anticipated challenges and potential for this exciting research are proposed.

Recent Progress in the Fabrication, Properties, and Devices of Heterostructures Based on 2D Materials

With a large number of researches being conducted on two?dimen?sional(2D) materials, their unique properties in optics, electrics, mechanics, and magnetics have attracted increasing attention. Accordingly, the idea of combining distinct functional 2D materials into heterostructures naturally emerged that pro?vides unprecedented platforms for exploring new physics that are not accessible in a single 2D material or 3D heterostructures. Along with the rapid development of controllable, scalable, and programmed synthesis techniques of high?quality 2D heterostructures, various heterostructure devices with extraordinary performance have been designed and fabricated, including tunneling transistors, photodetectors, and spintronic devices. In this review, we present a summary of the latest progresses in fabrications, properties, and applications of di erent types of 2D heterostruc?tures, followed by the discussions on present challenges and perspectives of further investigations.