Applications and potentials of machine learning in optoelectronic materials research:An overview and perspectives

Optoelectronic materials are essential for today's scientific and technological development,and machine learning provides new ideas and tools for their research.In this paper,we first summarize the development history of optoelectronic materials and how materials informatics drives the innovation and progress of optoelectronic materials and devices.Then,we introduce the development of machine learning and its general process in optoelectronic materials and describe the specific implementation methods.We focus on the cases of machine learning in several application scenarios of optoelectronic materials and devices,including the methods related to crystal structure,properties(defects,electronic structure)research,materials and devices optimization,material characterization,and process optimization.In summarizing the algorithms and feature representations used in different studies,it is noted that prior knowledge can improve optoelectronic materials design,research,and decision-making processes.Finally,the prospect of machine learning applications in optoelectronic materials is discussed,along with current challenges and future directions.This paper comprehensively describes the application value of machine learning in optoelectronic materials research and aims to provide reference and guidance for the continuous development of this field.

Flexible electronics and optoelectronics of 2D van der Waals materials

Flexible electronics and optoelectronics exhibit inevitable trends in next-generation intelligent industries,including healthcare and wellness,electronic skins,the automotive industry,and foldable or rollable displays.Traditional bulk-material-based flexible devices considerably rely on lattice-matched crystal structures and are usually plagued by unavoidable chemical disorders at the interface.Two-dimensional van der Waals materials(2D VdWMs)have exceptional multifunctional properties,including large specific area,dangling-bond-free interface,plane-to-plane van der Waals interactions,and excellent mechanical,electrical,and optical properties.Thus,2D VdWMs have considerable application potential in functional intelligent flexible devices.To utilize the unique properties of 2D VdWMs and their van der Waals heterostructures,new designs and configurations of electronics and optoelectronics have emerged.However,these new designs and configurations do not consider lattice mismatch and process incompatibility issues.In this review,we summarized the recently reported 2D VdWM-based flexible electronic and optoelectronic devices with various functions thoroughly.Moreover,we identified the challenges and opportunities for further applications of 2D VdWM-based flexible electronics and optoelectronics.

Universal memory based on phase-change materials:From phase-change random access memory to optoelectronic hybrid storage

The era of information explosion is coming and information need to be continuously stored and randomly accessed over long-term periods,which constitute an insurmountable challenge for existing data centers.At present,computing devices use the von Neumann architecture with separate computing and memory units,which exposes the shortcomings of“memory bottleneck”.Nonvolatile memristor can realize data storage and in-memory computing at the same time and promises to overcome this bottleneck.Phase-change random access memory(PCRAM)is called one of the best solutions for next generation non-volatile memory.Due to its high speed,good data retention,high density,low power consumption,PCRAM has the broad commercial prospects in the in-memory computing application.In this review,the research progress of phase-change materials and device structures for PCRAM,as well as the most critical performances for a universal memory,such as speed,capacity,and power consumption,are reviewed.By comparing the advantages and disadvantages of phase-change optical disk and PCRAM,a new concept of optoelectronic hybrid storage based on phase-change material is proposed.Furthermore,its feasibility to replace existing memory technologies as a universal memory is also discussed as well.

Research and Development of Electronic and Optoelectronic Materials in China

A review on the research and development of electronic and optoelectronic materials in China, including the main scientific activities in this field, is presented. The state\|of\|the\|arts and prospects of the electronic and optoelectronic materials in China are briefly introduced, such as those of silicon crystals, compound semiconductors, synthetic crystals,especially nonlinear optical crystals and rare\|earth permanent magnets materials, etc., with a greater emphasis on Chinese scientist’s contributions to the frontier area of nanomaterials and nanostructures in the past few years. A new concept of the trip chemistry proposed by Dr.Liu Zhongfan from Peking University has also been described. Finally the possible research grants and the national policy to support the scientific research have been discussed.

Organic optoelectronics:materials,devices and applications

The interest in organic materials for optoelectronic devices has been growing rapidly in the last two decades. This growth has been propelled by the exciting advances in organic thin films for displays, low-cost electronic circuits, etc. An increasing number of products employing organic electronic devices have become commercialized, which has stimulated the age of organic optoelectronics. This paper reviews the recent progress in organic optoelectronic technology. First, organic light emitting electroluminescent materials are introduced. Next, the three kinds of most important organic optoelectronic devices are summarized, including light emitting diode, organic photovoltaic cell, and photodetectors. The various applications of these devices are also reviewed and discussed in detail. Finally, the market and future development of optoelectronic devices are also demonstrated.

Preface to the Special Issue on Perovskite Semiconductor Optoelectronic Materials and Devices

Halide perovskite,a novel semiconductor material,was initially used in solar cells since 2009,and tremendous progresses have been witnessed in the last decade.The power conversion efficiency of the single perovskite solar cells has been incredibly increased up to 25.2%,and close to 30%efficiency was realized in perovskite/silicon tandem solar cells.Recently,the application of perovskite has been extended to the light-emitting diodes and photo-detectors.

The n-type Si-based materials applied on the front surface of IBC-SHJ solar cells

Interdigitated back contact silicon hetero-junction(IBC-SHJ) solar cells exhibit excellent performance owing to the IBC and SHJ structures.The front surface field(FSF) layer composed of electric field passivation and chemical passivation has been proved to play an important role in IBC-SHJ solar cells.The electric field passivated layer n^+-a-Si: H, an n-type Si alloy with carbon or oxygen in amorphous phase, is simulated in this study to investigate its effect on IBC-SHJ.It is indicated that the n^+-a-Si: H layer with wider band gap can reduce the light absorption on the front side efficaciously,which hinders the surface recombination of photo-generated carriers and thus contributes to the improvement of the short circuit current density Jsc.The highly doped n^+-a-Si: H can result in the remakable energy band bending, which makes it outstanding in the field passivation, while it makes little contribution to the chemical passivation.It is noteworthy that when the electric field intensity exceeds 1.3 × 10^5 V/cm, the efficiency decrease caused by the inferior chemical passivation is only 0.16%.In this study, the IBC-SHJ solar cell with a front n^+-a-Si: H field passivation layer is simulated, which shows the high efficiency of 26% in spite of the inferior chemical passivation on the front surface.

Progress of Si-based Optoelectronic Devices

Si-based optoelectronics is becoming a very active research area due to its potential applications to optical communications.One of the major goals of this study is to realize all-Si optoelectronic integrated circuit.This is due to the fact that Si-based optoelectronic technology can be compatible with Si microelectronic technology.If Si-based optoelectronic devices and integrated circuits can be achieved,it will lead to a new informational technological revolution.In the article,the current developments of this exciting field are mainly reviewed in the recent years.The involved contents are the realization of various Si-based optoelectronic devices,such as light-emitting diodes,optical waveguides devices,Si photonic bandgap crystals,and Si laser,etc.Finally,the developed tendency of all-Si optoelectronic integrated technology are predicted in the near future.

p‑Type Two‑Dimensional Semiconductors:From Materials Preparation to Electronic Applications

Two-dimensional(2D)materials are regarded as promising candidates in many applications,including electronics and optoelectronics,because of their superior properties,including atomic-level thickness,tunable bandgaps,large specific surface area,and high carrier mobility.In order to bring 2D materials from the laboratory to industrialized applications,materials preparation is the first prerequisite.Compared to the n-type analogs,the family of p-type 2D semiconductors is relatively small,which limits the broad integration of 2D semiconductors in practical applications such as complementary logic circuits.So far,many efforts have been made in the preparation of p-type 2D semiconductors.In this review,we overview recent progresses achieved in the preparation of p-type 2D semiconductors and highlight some promising methods to realize their controllable preparation by following both the top-down and bottom-up strategies.Then,we summarize some significant application of p-type 2D semiconductors in electronic and optoelectronic devices and their superiorities.In end,we conclude the challenges existed in this field and propose the potential opportunities in aspects from the discovery of novel p-type 2D semiconductors,their controlled mass preparation,compatible engineering with silicon production line,high-κdielectric materials,to integration and applications of p-type 2D semiconductors and their heterostructures in electronic and optoelectronic devices.Overall,we believe that this review will guide the design of preparation systems to fulfill the controllable growth of p-type 2D semiconductors with high quality and thus lay the foundations for their potential application in electronics and optoelectronics.

Organic near-infrared optoelectronic materials and devices:an overview

Near-infrared(NIR)light has shown great potential for military and civilian applications owing to its advantages in the composition of sunlight,invisibility to human eyes,deeper penetration into biological tissues,and low optical loss in optical fibers.Therefore,organic optoelectronic materials that can absorb or emit NIR light have aroused great scientific interest in basic science and practical applications.Based on these NIR organic optoelectronic materials,NIR optoelectronic devices have been greatly improved in performance and application.In this review,the representative NIR organic optoelectronic materials used in organic solar cells,organic photodetectors,organic light-emitting diodes,organic lasers,and organic optical waveguide devices are briefly introduced,and the potential applications of each kind of device are briefly summarized.Finally,we summarize and take up the development of NIR organic optoelectronic materials and devices.

Organic-inorganic hybrid materials and architectures in optoelectronic devices: Recent advancements

Organic-inorganic hybrids are next-generation materials for use in high-performance optoelectronic devices owing to their adaptabilities in terms of design and properties.This article reviews the application of hybrid materials and layers in several widely used optoelectronic devices,i.e.,light amplification by stimulated emission of radiation(LASER),solar cells,and light-emitting diodes(LEDs).The effects of the incorporation of inorganic particles on photostability and optical gain are analyzed in the first section with reference to dye and perovskite lasers.Second,the strategies used in blending inorganic nanostructures into organic solar cells and bulk heterojunctions are analyzed.The use of various organic layers as electron-and hole-transport materials in Si heterojunction solar cells is reviewed in detail.Finally,the benefits of the presence of organic components in quantum-dot-and perovskite-based LEDs are derived from the analysis.The integration of organic and inorganic components with optimal interfaces and morphologies is a challenge in developing hybrid materials with improved efficiencies.

Synthesis of a New Optoelectronic Material Based on Oriented Adsorption of Dyes to Nanoparticles Surface

Synthesis of the optoelectronic storage material with structure for coating by nanosized metal and azo-dye was reported. The characterization of composites was made by using transmission electron microscope （TEM）, ultraviolet-visible spectrometer （UV-Vis） and thermogravity analyzer （TGA）. It is found that, due to the specific structure, in which azo-dye molecules are oriented and adsorbed on the spherical surface of nanosized metal, the absorption maximum of azo-dye methyl orange shift towards shorter wavelength band. The experimental results show that the proposed technique here wouM offer a promising way to synthesize short wavelength optoelectronic storage material by doping of metal nanoparticles coated with dyes in polymer. Furthermore, the composites based on the structure can present excellent thermal properties suitable for the requirements of optical storage. This new type of material is capable of matching semiconductor laser （GaN） in optoelectronic storage technology.

Two-Dimensional Materials in Large-Areas: Synthesis, Properties and Applications

Large-area and high-quality two-dimensional crystals are the basis for the development of the next-generation electronic and optical devices.The synthesis of two-dimensional materials in wafer scales is the first critical step for future technology uptake by the industries;however,currently presented as a significant challenge.Substantial efforts have been devoted to producing atomically thin two-dimensional materials with large lateral dimensions,controllable and uniform thicknesses,large crystal domains and minimum defects.In this review,recent advances in synthetic routes to obtain high-quality two-dimensional crystals with lateral sizes exceeding a hundred micrometres are outlined.Applications of the achieved large-area two-dimensional crystals in electronics and optoelectronics are summarised,and advantages and disadvantages of each approach considering ease of the synthesis,defects,grain sizes and uniformity are discussed.

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.

Tunable Electronic and Optical Properties of 2D Monoelemental Materials Beyond Graphene for Promising Applications

As a new type of two-dimensional(2D)materials,monoelemental 2D materials have the atomic structure similar to graphene,and their excellent optical and electronic properties have potential applications in many fields.To date,many studies based on monoelemental 2D materials have been reported,and excellent performance has been demonstrated in various fields.The monoelemental 2D materials that have been reported so far are mainly distributed in the groupⅢA,ⅣA,ⅤA,andⅥA.Because of their structural similarities to graphene,they are commonly referred to as"Xenes."Here,we have comprehensively reviewed the research progress of monoelemental 2D materials.In this review,we explore the structure,properties,and practical applications of these monoelemental 2D materials.First,the classification,structural features,optical properties,electronic characteristics,and regulating mechanism of these monoelemental 2D materials are introduced.Then,the practical application and research progress of monoelemental 2D materials in various fields are reviewed comprehensively,especially including photoelectric catalysis,solar cells,and other energy fields.This review will give readers a more all-sided understanding of monoelemental 2D materials and have some guiding significance for their further development.

Negative photoconductivity in low-dimensional materials

In recent years,low-dimensional materials have received extensive attention in the field of electronics and optoelectronics.Among them,photoelectric devices based on photoconductive effect in low-dimensional materials have a broad development space.In contrast to positive photoconductivity,negative photoconductivity(NPC)refers to a phenomenon that the conductivity decreases under illumination.It has novel application prospects in the field of optoelectronics,memory,and gas detection,etc.In this paper,we review reports about the NPC effect in low-dimensional materials and systematically summarize the mechanisms to form the NPC effect in existing low-dimensional materials.

Research progress of optoelectronic devices based on two-dimensional MoS_(2) materials

Molybdenum disulfide(MoS_(2))is a widely used optoelectronic material with exceptional electrical,magnetic,optical,and mechanical properties.Due to the quantum confinement effect,high absorption coefficient,high surface-volume ratio,and tunable bandgap,nanoMoS_(2)-based devices exhibit size-dependent and novel optoelectronic properties,such as excellent photoluminescence and high anisotropic electrical,mechanical,and thermal properties.This review focuses mainly on the latest progress of optoelectronic device applications based on two-dimensional(2D)nano-MoS_(2).Various advanced devices,such as sensors,photodetectors,light-emitting diodes(LEDs),memory applications,and field-effect transistors(FETs)are considered.The review will provide a new perspective in promoting the development of 2D nanomaterial-based photoelectric applications.

Cellulose Nanocrystals-based Chiroptical Materials

Chiroptical materials are widely used in photonic devices,enantioselective catalysis and bio-sensors.Cellulose-base chiroptical materials with multilength scale structural hierarchy and unique light manipulation ability found in nature provide inspiration for materials design.Cellulose nanocrystals(CNC)display twisted rod morphology and hierarchical chirality.Leveraging the evaporation-induced self-assembly of negatively charged CNC,a broad realm of CNC-based chiroptical materials featuring one-dimensional photonic bandgap and novel chiroptical properties have been developed,which are of scientific and technological significance.Here we presented a brief overview on CNC-based chiroptical materials by evaporation-induced self-assembly,showed energy and chirality transfer in a host-guest environment leading to photonic bandgap modulation of optoelectronic properties,outlined novel chiroptical phenomena and their underlying principles,and demonstrated the application potentials of the CNC-based chiroptical materials.

Light–matter interaction of 2D materials:Physics and device applications

In the last decade, the rise of two-dimensional （2D） materials has attracted a tremendous amount of interest for the entire field of photonics and opto-electronics. The mechanism of light-matter interaction in 2D materials challenges the knowledge of materials physics, which drives the rapid development of materials synthesis and device applications. 2D materials coupled with plasmonic effects show impressive optical characteristics, involving efficient charge transfer, plas- monic hot electrons doping, enhanced light-emitting, and ultrasensitive photodetection. Here, we briefly review the recent remarkable progress of 2D materials, mainly on graphene and transition metal dichalcogenides, focusing on their tunable optical properties and improved opto-electronic devices with plasmonic effects. The mechanism of plasmon enhanced light-matter interaction in 2D materials is elaborated in detail, and the state-of-the-art of device applications is compre- hensively described. In the future, the field of 2D materials holds great promise as an important platform for materials science and opto-electronic engineering, enabling an emerging interdisciplinary research field spanning from clean energy to information technology.

A New Class of Biodegradable Organic Optoelec-tronic Materials:α-Oligofurans

Organic optoelectronic materials have received considerable attention due to their great potentials in electronic devices,such as organic field-effect transistors(OFETs),organic light-emit-ting diodes(OLED)and organic photovoltaic cells(OPV).Besides,their fascinating properties of flexibility,biocompatibility,molecular diversity,low-cost and solution processability bring new opportunities in bioelectronics in the past decade.While almost all known organic optoelectronic materials are obtained from unrenewable fossil resources and nondegradable,a new family of organic optoelectronic materials is now emerging,which can be obtained from green plants and are biodegradable.Meanwhile,they exhibit excellent optoelectronic properties.This review summarized the synthesis and important molecular properties of this new class of biodegradable organic opto-electronic materials:α-oligofurans.Recent progress of furan-based materials and the existing chal-lenges are also discussed to stimulate further advances in the study of this class of materials.