Organic Synaptic Transistors: The Evolutionary Path from Memory Cells to the Application of Artificial Neural Networks

The progress of neural synaptic devices is experiencing an era of explosive growth. Given that the traditional storage system has yet to overcome the von Neumann bottleneck, it is critical to develop hardware with bioinspired information processing functions and lower power consumption. Transistors based on 2D materials, metal oxides, and organic materials have been adopted to mimic the synapse of a human brain, due to their high plasticity, parallel computing, integrated storage, and system information processing. Among these materials used to build transistors, organic semiconductors are considered to be the most promising candidate for neural synaptic devices and bio-electronics, owing to their easy processing, mechanical flexibility, low cost, good bio-compatibility, and ductility. This review focuses on the recent advances in organic synaptic devices with various structures, materials, and working mechanisms. The applications of artificial neural networks that integrate multiple organic synaptic transistors are also concretely discussed. Finally, the challenges that organic synaptic devices currently face are discussed and future developments are forecast.     

Natural Materials for Sustainable Organic Solar Cells: Status and Challenge

The exploitation of natural materials has received growing attention because of the needs of environmental sustainability. In contrast to petroleum-based synthetic materials, natural materials possess significant advantages of abundant, low-cost, degradable, and renewable. Here, the recent research status of natural materials as flexible substrate, cathode interfacial material, and anode interfacial material for organic photovoltaics (OPVs) are first presented. Then, the confronted key challenges that limit the widespread application of natural materials for OPVs is summarized, including complex multilength scaled aggregation morphology, non-conjugated structure, and unclear working mechanism. Finally, their potential solutions from the perspective of chemical structure are proposed for constructing efficient OPVs. It is believed that natural materials have a broad landscape in low-cost and green manufacturing technology for OPVs in the future.     

Advanced Thermoelectric Materials for Flexible Cooling Application

Flexible cooling devices, which aim to fulfill the essential requirement of complex working environments and enable local heat dissipation, have become the cutting-edge area of refrigeration technology. Thermoelectric (TE) material represents a promising candidate for various flexible cooling applications, including wearable personal thermoregulation devices. With the increasing interest in the Peltier effect of conductive polymers and inorganic films on flexible substrates, flexible cooling devices have undergone rapid development. Herein, the fundamental mechanisms, basic parameters, and temperature measurement techniques for evaluating the cooling performance are summarized. Moreover, recent progress on TE materials, such as flexible inorganic and organic materials for Peltier cooling studies, is reviewed. More importantly, insights are provided into the key strategies for high-performance Peltier devices. The final part details the existing challenges and perspectives on flexible TE cooling to inspire additional research interests toward the advancement of refrigeration technology.     

Recent Advances in 1D Organic Solid‐State Lasers

Organic solid‐state lasers (OSSLs) based on 1D organic crystals have attracted broad attention from researchers owing to the importance of potential applications in optoelectronic fields. 1D OSSLs can be fabricated from various organic molecules under the function of weak intermolecular interactions via numerous methods. The lasing performance of 1D OSSLs can be tuned toward novel optoelectronic applications by modifying the primary 1D morphology through constructing heterogeneous 1D architectures. Here, the recent advances of 1D OSSLs from the aspects of materials, fabrication methods, as well as some enlightening examples of 1D OSSLs with advanced laser performances are reviewed, and an outlook is given providing inspiration for the future development of 1D OSSLs with desired performances.     

Covalent Organic Frameworks for Batteries

Covalent organic frameworks (COFs) have emerged as an exciting new class of porous materials constructed by organic building blocks via dynamic covalent bonds. They have been extensively explored as potentially superior candidates for electrode materials, electrolytes, and separators, due to their tunable chemistry, tailorable structures, and well-defined pores. These features enable rational design of targeted functionalities, facilitate the penetration of electrolytes, and enhance ion transport. This review provides an in-depth summary of the recent progress in the development of COFs for diverse battery applications, including lithium-ion, lithium–sulfur, sodium-ion, potassium-ion, lithium–CO₂, zinc-ion, zinc–air batteries, etc. This comprehensive synopsis pays particular attention to the structure and chemistry of COFs and novel strategies that have been implemented to improve battery performance. Additionally, current challenges, possible solutions, and potential future research directions on COFs for batteries are discussed, laying the groundwork for future advances for this exciting class of material.     

A Review on Encapsulation Technology from Organic Light Emitting Diodes to Organic and Perovskite Solar Cells

Organic light emitting diodes (OLEDs) employing organic thin-film based emitters have attracted tremendous attention due to their widespread applications in lighting and as displays in mobile devices and televisions. The novel thin-film photovoltaic techniques using organic or organic–inorganic hybrid materials such as organic photovoltaics (OPVs) and perovskite solar cells (PSCs) have become emerging competitive candidates with regard to the traditional photovoltaic techniques on account of high-efficiency, low-cost, and simple manufacturing processing properties. However, OLEDs, OPVs, and PSCs are vulnerable to the undesired degradation induced by moisture and oxygen. To afford long-term stability, a robust encapsulation technique by employing materials and structures that possess high barrier performance against oxygen and moisture must be explored and employed to protect these devices. Herein, the recent progress on specific encapsulation materials and techniques for three types of devices on the basis of fundamental understanding of device stability is reviewed. First, their degradation mechanisms, as well as, influencing factors are discussed. Then, the encapsulation technologies and materials are classified and discussed. Moreover, the advantages and disadvantages of various encapsulation technologies and materials coupled with their encapsulation applications in different devices are compared. Finally, the ongoing challenges and future perspectives of encapsulation frontier are provided.     

基于二维半导体材料光电器件的研究进展

近年来,二维半导体材料因其独特的晶体结构和优良的电子、光电特性吸引了众多科研人员的关注。利用这些材料作为有源沟道,制备出了许多新颖的器件结构,性能较传统器件有很大的提升。在各种器件应用中,基于二维材料的光电探测器由于能够实现红外及太赫兹波段的光探测,得到了最为广泛的研究。综述了近年来二维材料在光电器件领域的应用,介绍了光电探测器的主要参数,从电极制备、异质结构筑、量子点和分子掺杂、表面等离激元耦合以及界面屏蔽5方面介绍了目前在二维材料中调控光电性能的方法,对已有方法进行了总结,并且对未来的发展进行了讨论。     

Application of 2D MXene in Organic Electrode Materials for Rechargeable Batteries: Recent Progress and Perspectives

Organic electrode materials (OEMs) are emerging green power because of the promising advantages such as environmental friendliness, abundant sources, easy recycling, and structural diversity. However, several inherent issues, including low electronic conductivity, dissolution of active materials, and particle pulverization restrict their practical application. MXene, as a novel 2D material has exhibited enormous potential to solve the issues of OEMs due to its high conductivity, unique structure, exceptional mechanical property, and abundant surface groups. Up to now, various effective strategies have been presented and achieved positive effects, such as constructing heterojunction structures, in situ assembly, dip-coating, preparing free-standing MXene paper, etc. Nonetheless, comprehensive review of the progress and status is rare. Herein, an overview of the application of MXene in organic electrode materials for rechargeable batteries is systematically put forward. Meanwhile, recent progress and future development directions are presented. This review can serve as a guide for future research.     

有机共混结构太阳电池的阴极界面修饰的研究进展

太阳电池阴极界面的有效修饰能改善器件中载流子的收集与传输,从而提高太阳电池能量转换效率。对于高效、稳定的有机光伏器件来说,合理选择界面修饰材料至关重要,它已成为有机光伏领域研究的重点内容。文章综述了近年来有机共混结构太阳电池阴极界面修饰的研究进展,介绍了各种阴极界面的修饰方法及原理,阐述了国内外有机共混结构太阳电池阴极界面修饰的研究现状及存在问题,为高性能有机太阳电池的研究提供了有价值的参考。     

Preparation,Properties, and Applications of Low-Dimensional Molecular Organic Nanomaterials

In recent years, great progress has been made in research and development of small-molecule organic materials with various low-dimensional nanostructures. This paper presents a comprehensive review of recent research progress in this field, including preparation, electronic and optoelectronic properties and applications. First, an introduction gives to the reprecipitation, soft templates methods, and progress in synthesis and morphological control of low-dimensional small-molecule organic nanomaterials. Their unique optical and electronic properties and research progress in these aspects are reviewed and discussed in detail. Applications based on low-dimensional small-molecule organic nanomaterials are briefly described. Finally, some perspectives to the future development of this field are addressed.     

Advanced Functional Electroactive and Photoactive Materials for Monitoring the Environmental Pollutants

Functional materials with attractive electronic and photoelectronic properties show great promise in various fields. In recent decades, tremendous research efforts have been devoted to the design of photoactive and electroactive materials for qualitative and quantitative analysis of environmental pollutants. This review gives a concise overview on the fundamentals and recent research progress of functional material-based electrochemical and photoelectrochemical technology for environmental pollutant monitoring. The rational design of functional photoactive and electroactive materials with promoted electrochemical properties and basic signaling strategies for electrochemical and photoelectrochemical sensors are presented. Based on these insights, very recent achievements for electrochemical and photoelectrochemical environmental pollutant sensors are summarized from the viewpoint of various functional materials. At last, critical challenges and future research perspectives in this field are proposed and discussed to provide a backdrop for future research.     

Advanced Flexible Materials from Nanocellulose

With the increase of environmental pollution and depletion of fossil fuel resources, the utilization of renewable biomass resources for developing functional materials or fine chemicals is of great value and has attracted considerable attention. Nanocellulose, as a well-known renewable nanomaterial, is regarded as a promising nano building block for advanced functional materials owing to its unique structure and properties, as well as natural abundance. Typically, its high mechanical strength, structural flexibility, reinforcing capabilities, and tunable self-assembly behavior makes it highly attractive to fabricate flexible materials for various applications. Herein, the recent progress in the design, properties, and applications of advanced flexible materials from nanocellulose is comprehensively summarized. The preparation and properties of nanocellulose are first briefly introduced and discuss its merits in fabricating flexible materials. Then, various advanced flexible materials from nanocellulose are introduced, and the critical role of nanocellulose in constructing flexible materials is highlighted based on its intrinsic properties. After that, their applications in energy storage, electronics, sensor, biomedical, thermally insulating, photonic devices, etc., are presented. At last, the outlook of the current challenges and future perspectives for developing nanocellulose-derived flexible materials are discussed.     

Biocatalytic Metal–Organic Frameworks: Prospects Beyond Bioprotective Porous Matrices

Biocatalytic metal–organic framework (MOF) composites, synthesized by interfacing MOFs with biocatalytic components, possessing the unprecedented synergetic properties that are hard to achieve via conventional strategies, represent one of the next‐generation composite materials for diverse biotechnological applications. Research on the applications of biocatalytic MOFs is still in its preliminary stage, with a wide variety of studies focusing on the bioprotection role of MOFs. However, their diversity of building units, molecular‐scale tunability, modular synthetic routes, and more detailed understanding of the heterogeneous MOF‐biointerface could even lead to completely new applications and potentials beyond the current imagination. The most recent progress in biocatalytic MOFs presents ground‐breaking applications in smart and tunable biocatalysis, precision nanomedicine, vaccine and gene delivery, biosensing, and nano‐biohybrids. Herein, the general and advanced synthesis strategies for improving the material properties of biocatalytic MOFs, from tuning biocatalytic activity to framework stability to synergistic properties with other materials, are summarized. Then, the latest state‐of‐the‐art applications of the biocatalytic MOF systems and recent advanced developments that are shaping this emerging field are surveyed. Finally, to define promising research directions, a critical evaluation and future prospects for the potential applications of biocatalytic MOFs are provided.     

Opportunities and Challenges in Precise Synthesis of Transition Metal Single-Atom Supported by 2D Materials as Catalysts toward Oxygen Reduction Reaction

Transition metal single-atom catalysts (SACs) are currently a hot area of research in the field of electrocatalytic oxygen reduction reaction (ORR). In this review, the recent advances in transition metal single-atom supported by 2D materials as catalysts for ORR with high performance are reported. Due to their large surface area, uniformly exposed lattice plane, and adjustable electronic state, 2D materials are ideal supporting materials for exploring ORR active sites and surface reactions. The rational design principles and synthetic strategies of transition metal SACs supported by 2D materials are systematically introduced while the identification of active sites, their possible catalytic mechanisms as well as the perspectives on the future of transition metal SACs supported by 2D materials for ORR applications are discussed. Finally, according to the current development trend of ORR catalysts, the future opportunities and challenges of transition metal SACs supported by 2D materials are summarized.     

Recent Progress in Functional Dye-Doped Liquid Crystal Devices

As a typical representative of dopants, organic functional dyes have demonstrated their significant roles in novel smart liquid crystal (LC) devices, and dye-doped LCs have also been a source of inspiration for scientists to design and fabricate stimuli-gated materials or devices for envisioned applications in a wide range of areas. In this review, the focus on dichroic dyes, fluorescent dyes, and photothermal dyes, and the recent progress of the LC devices employing these dyes as dopants are overviewed. The review highlights the developments of the novel LC devices doped with these dyes. The structures, designs, and applications of these devices are outlined. The underlying principles of dichroic dyes, fluorescent dyes, and photothermal dyes which are utilized as functional dopants in LC devices are first introduced. Subsequently, the novel developments of functional dye-doped LC devices in the application fields of smart windows, attenuators for augmented reality (AR) systems, color-changeable textiles, dichroic color filters, dual-mode circular polarizers, chirality detectors, optical limiters, switchable luminescent solar concentrators, multiple information encryption, anti-counterfeiting, photo-addressed transparent displays, circularly polarized luminescence, tunable lasers, and light-driven soft actuators are discussed. Finally, the challenge and the strategies for the future improvement of dye-doped LC devices are also discussed.     

Smart Nanostructured Materials based on Self‐Assembly of Block Copolymers

Nanoscale fabrication of smart materials relying on the molecular self‐assembly of block copolymers (BCPs) has been recognized as a valuable platform for various next‐generation functional structures. In this Progress Report, the recent advances in the BCP self‐assembly process, which has paved the way for viable applications of emerging nanotechnologies, are highlighted. Effective light‐induced self‐assembly based on photothermal annealing of high‐χ BCPs and conformal 3D surface nanopatterning exploiting chemically modified graphene flexible substrates are reviewed as the typical instances of advanced BCP‐based nanofabrication methodologies. Additionally, relevant potential application fields are suggested, namely, graphene nanoribbon field effect transistors, highly tunable refractive index metasurfaces for visible light, high‐sensitivity surface‐enhanced Raman spectroscopy, 2D transition metal dichalcogenide nanopatterning, sequential infiltration synthesis, and organic photovoltaics. Finally, the future research direction as well as innovative applications of these smart nanostructured materials is proposed.     

Layered Materials in the Magnesium Ion Batteries: Development History,Materials Structure,and Energy Storage Mechanism

Layered crystal materials have blazed a promising trail in the design and optimization of electrodes for magnesium ion batteries (MIBs). The layered crystal materials effectively improve the migration kinetics of the Mg²⁺ storage process to deliver a high energy and power density. To meet the future demand for high-performance MIBs, significant work has been applied to layered crystal materials, including crystal modification, mechanism investigation, and micro/nanostructure design. Herein, this review presents a comprehensive overview of layered crystal materials applied to MIBs, from development history to current applications. It focuses on the relationship between the layered crystal structure and the energy storage mechanism. Meanwhile, recent achievements in the design principles of layered crystal materials and their application to electrodes are summarized. Finally, future perspectives on the application of layered materials in MIBs are presented. The overview of the development process and structural characteristics contributes to a thorough understanding of these materials, while a discussion of design strategies and practical applications can inspire further research. Therefore, this review provides guidance and assistance for constructing high-performance MIBs.     

n‐Type Quinoidal Oligothiophene‐Based Semiconductors for Thin‐Film Transistors and Thermoelectrics

Organic electronic devices have gained immense popularity in the last 30 years owing to their increasing performance. Organic thin‐film transistors (OTFTs) are one of the basic organic electronic devices with potential industrial applications. Another class of devices called organic thermoelectric (OTE) materials can directly transform waste heat into usable electrical power without causing any pollution. p‐Type transistors outperform n‐type transistors because the latter requires a lower orbital energy level for efficient electron injection and stable electron transport under ambient conditions. Aromatic building blocks can be utilized in constructing n‐type semiconductors. Quinoidal compounds are another promising platform for optoelectronic applications because of their unique properties. Since their discovery in 1970s, quinoidal oligothiophene‐based n‐type semiconductors have drawn considerable attention as candidates for high‐performance n‐type semiconductors in OTFTs and OTEs. Herein, the development history of quinoidal oligothiophene‐based semiconductors is summarized, with a focus on the molecular design and the influence of structural modification on molecular packing and thus the device performance of the corresponding quinoidal oligothiophene‐based semiconductors. Insights on the potential of quinoidal oligothiophenes for high‐performance n‐type OTFTs and OTEs are also provided.     

Enabling Efficient Blue-Emissive Circularly Polarized Luminescence by In Situ Crafting of Chiral Quasi-2D Perovskite Nanosheets within Polymer Nanofibers

Chiral perovskite materials have intrigued enormous interests because of their appealing chiroptical properties and tailorable non-centrosymmetric structures. However, it remains challenging to realize high-efficiency blue emissive circularly polarized luminescence (CPL) of intrinsic chiral perovskite nanomaterials at room temperature. Herein, a robust and versatile electrospinning strategy is reported for in situ construction of chiral 2D and quasi-2D perovskite nanosheets (PNSs) protected in polymer hybrid nanofibers. It is found that quasi-2D chiral PNS/polymer possesses inherent chirality and enhanced CPL properties at room temperature compared to 2D counterparts. Notably, CPL emission color of chiral quasi-2D PNS/polymer can be tuned from deep blue to sky blue, and a high luminescence dissymmetry values up to −8.0 × 10⁻³ can be achieved. Different perovskites, polymers, and nanofibrous structures are expanded to explore the universality of polymer protected PNSs. Significantly, compared to spin-coated film, the stabilities of quasi-2D PNS/polymer film are greatly improved due to the effective protection of polymer. The obtained PNS/polymer hybrid nanofiber films can be conveniently implemented for circularly polarized light emitting diode devices. This study may open up a new avenue for the scalable fabrication of chiral perovskite nanomaterials of interest and their applications in the CPL related fields.     

Organic Thermoelectric Materials: Niche Harvester of Thermal Energy

Organic thermoelectric (OTE) materials promise convenient energy conversion between heat gradients and voltage with flexible and wearable power-supplying devices at a low price. Although a variety of OTE materials are investigated, the TE performance is still far from practical application. To achieve high TE performance, a thorough understanding of the structure–property relationship in OTE materials is necessary. In this comprehensive review, the fundamentals of OTEs are summarized, the recent achievements of OTE materials are reviewed, and the relationship between structure and properties in high-performance OTE materials is discussed. Furthermore, how the molecular backbones, side chains, energy levels, molecular packing, and heteroatom effect all play vital roles in thermoelectric properties is addressed. Finally, the future direction of research on OTE materials is envisaged.