树枝状分子应用于有机电致发光材料的研究进展

有机电致发光材料是光电信息功能材料领域的研究热点之一.相对于线性的有机小分子和高分子,作为有机电致发光材料,树枝状分子有着多方面的优势.分别从树枝状分子作为发光材料、电子传输材料、空穴传输材料和多功能载流子传输材料等4个方面简要介绍了树枝状分子在有机电致发光材料领域的研究进展,并进一步展望了树枝状分子未来的研究前景.     

基于共轭有机硼化合物的多功能发光材料的分子设计

设计了6种可作有机发光二极管(OLEDs)发光材料和空穴传输材料的π-共轭有机硼化合物。利用密度泛函(DFT)和含时密度泛函理论(TD-DFT)方法研究了它们的前线分子轨道、吸收光谱、荧光光谱以及电荷传输性质。通过前线分子轨道分析发现,所设计化合物的吸收和荧光发射导致的电子跃迁具有明显的分子内电荷转移特性。引入不同的π-共轭桥影响化合物的前线分子轨道能量、能隙、光学和电荷传输性质。同时,预测了所设计化合物的电子和空穴的迁移率。研究结果表明,所设计的π-共轭有机硼化合物有望成为性能良好的有机发光二极管的发光材料和空穴传输材料。     

有机电致发光器件的效率及寿命

有机电致发光器件的效率取决于电子和空穴的有效注入和复合.电极材料和有机材料的稳定性以及电极/有机层之间的界面处的相互作用是制约有机电致发光器件寿命的主要因素.     

水溶胶CdSe纳米复合器件电致发光特性的研究

以巯基乙酸为稳定剂在水相中制备了水溶胶CdSe纳米晶,透射电子显微镜表明了纳米晶的形态和尺寸大小.用表面活性剂将CdSe纳米晶从水相中转移到有机相中,将其与具有空穴传输性能的聚合物PVK互溶在一起作为电致发光器件的发光层,以Alq3作为电子传输层,在发光层与Alq3之间加入了空穴阻挡层BCP制备了多层电致发光器件,研究了不同CdSe/PVK配比下水溶胶CdSe纳米复合器件的电致发光特性,结果发现随着水溶胶CdSe纳米晶在纳米复合物中所占比例的降低,电致发光器件的发光强度有所提高,起亮电压有所降低.     

环境湿度对有机电致发光二极管功能材料的影响

随着有机电致发光二极管(OLED)市场化进程加快,有机光电功能材料的应用日趋广泛,但环境湿度对OLED功能材料影响的研究鲜有报道。以典型的空穴传输材料N,N′-bis-(1-naphthyl)-N,N′-biphenyl-1,1′-biphenyl-4,4′-diamine(NPB)为例,将其分别置于环境湿度为5%,20%,35%和50%,环境温度均为25℃的条件下24h,以其为空穴传输层构建绿色荧光OLED器件;系统调查了NPB材料不同存储环境湿度对OLED器件性能的影响。结果表明,随着NPB存储环境湿度不断增加(5%~50%),器件性能逐渐降低,其中最大电流效率由3.96cd/A降低到3.31cd/A。进一步地,单载流子器件的电流-电压特性表明,随着环境湿度的增加,NPB空穴传输性能逐渐增强,这加剧了OLED器件中空穴和电子传输性能的不平衡,导致器件效率较低。此外,分析了NPB薄膜光致发光(PL)光谱随着材料存储湿度的增加逐渐红移的现象,这可能是由于水分子的侵入,使得NPB分子的局域激发态转换为具有强烈电荷转移特征的激发态的结果。     

通过调节交联空穴传输材料三线态能级实现溶液法制备高效的热活化延迟荧光有机电致发光二极管（英文）

具有高三线态能级的交联空穴传输材料能够平衡发光层载流子的复合并有效抑制三线态激子的猝灭,对制备高性能溶液法有机电致发光二极管具有重要意义.本文设计合成了两种具有不同母核的新型交联空穴传输材料, V-p-DBT和V-p-DBF.与已报道的交联空穴传输材料V-p-TPD相比,二苯并噻吩和二苯并呋喃母核的引入增加了分子的扭转角,使两种化合物具有更高的三线态能级,分别为2.57和2.64 e V.通过瞬态荧光光谱证明它们能够有效地抑制三线态激子的猝灭.交联的空穴传输层表现出优异的抗溶剂能力和溶液工艺所需的理化性质.其中,基于V-p-DBF的绿色热活化延迟荧光有机发光二极管获得了79.94 cd A-1的最大电流效率和24.35%的最大外量子效率.这项工作为实现溶液法制备的有机电致发光二极管提供了一种新的分子设计策略.     

基于有机金属卤化物钙钛矿材料的全固态太阳能电池研究进展

作为太阳能电池的光吸收剂,有机金属卤化物钙钛矿材料不仅具有高效的光吸收能力和载流子迁移率,还具有独特的双极性特征,能同时传输电子和空穴,使其成为优异的光伏材料,掀起了基于钙钛矿材料太阳能电池的研究热潮。介绍了近几年来基于有机金属卤化物钙钛矿材料的全固态太阳能电池的发展情况,总结了有机金属卤化物钙钛矿材料的结构和特性,对目前几类典型的钙钛矿太阳能电池进行了讨论,并展望了全固态钙钛矿太阳能电池的产业化应用前景。     

空穴传输材料在高效钙钛矿太阳能电池中的发展演变

钙钛矿太阳能电池(PSCs)转换效率已从2009年的3.8%上升到2017年的22.7%,其快速的发展可能使光伏工业进入革命新阶段。空穴传输材料(HTM)是构成高效钙钛矿太阳能电池的重要组成部分,开发和设计导电性好、成本低、稳定性好的空穴传输层材料对钙钛矿太阳能电池的研究显得非常重要。本文将近几年应用于钙钛矿太阳能电池中较高效的空穴传输材料归纳为有机小分子类、有机聚合物类和无机材料类,同时也介绍了无空穴传输层的钙钛矿电池。详细评述了基于各类空穴传输材料的钙钛矿太阳能电池的光电性能及稳定性,重点讨论了HOMO能级、空穴迁移率、添加剂的掺杂等因素对钙钛矿太阳能电池的影响。最后指出了空穴传输材料未来的研究重点和发展趋势。     

"光子-买一赠三”--简评有机三线态电致发光材料与器件进展*

有机电致发光材料与器件的研究已取得了重要进展,但要实现高信息含量的应用,器件的稳定性和效率仍须进一步提高。基于量子统计理论的研究结果表明,只有25%的电子空穴复合能量生成单线态激子,对于一个纯荧光的发光材料,在理论上,其器件效率的上限是光致发光效率的25%。三线态发光材料的应用,理论上可有效利用所有的复合能量,从而大幅度提高器件效率,目前已成为有机电致发光领域的研究热点。综述了有机三线态电致发光材料与器件的进展。     

基于萤火虫烯醇式氧化荧光素的一系列衍生物的结构和光学性质

通过密度泛函理论(DFT)MPW3PBE泛函,对甲基、甲氧基、氰基、氟原子、氨基、硝基取代的萤火虫生物发光底物烯醇式氧化荧光素进行了全优化。计算了他们的电离能(IP)、电子亲和势(EA)、空穴抽取能(HEP)、电子抽取能(EEP)、空穴和电子重组能(λ),评估了它们的空穴和电子传输能力。用含时密度泛函理论(TDDFT)MPW3PBE/6-31+G(d)方法计算了吸收光谱,优化了最低单重态S1,最终研究了它们的荧光光谱。理论计算结果表明,E-CN是具有双重功能的OLEDs材料的优良候选者,即可同时作为电子传输层和发光层材料。E-NO2、E-F和E-OCH3可以作为电子传输材料。而E-NH2可作为空穴传输材料。     

Noncovalent Functionalization of Pnictogen Surfaces: From Small Molecules to 2D Heterostructures

Beyond graphene, 2D pnictogen polymers are rapidly growing among the family of 2D materials. Due to their unique properties, this group has received considerable interest in recent years. Those properties include tunable electronic band gaps, high charge carrier mobility, and in‐plane anisotropic properties. This Review covers the noncovalent functionalization of pnictogen surfaces considering experimental and theoretical studies. Noncovalent functionalization is of great importance for effective modulation of the electronic structure of these materials as well as improvement of their stability toward surface oxidation. This Review highlights their noncovalent modification by organic molecules, in which enhanced surface stability of phosphorene and generated functionalized materials for applications in biomedical, supercapacitors, energy storage, and biosensors. Moreover, the noncovalent interactions with small molecules show its significance for sensing applications. Lastly, the interactions of pnictogen sheets with other 2D materials and their applications for van der Waals heterostructure formation are discussed. Current state‐of‐the‐art as well as future perspectives in this field are covered.     

Modulating the Charge Transport in 2D Semiconductors via Energy‐Level Phototuning

The controlled functionalization of semiconducting 2D materials (2DMs) with photoresponsive molecules enables the generation of novel hybrid structures as active components for the fabrication of high‐performance multifunctional field‐effect transistors (FETs) and memories. This study reports the realization of optically switchable FETs by decorating the surface of the semiconducting 2DMs such as WSe₂ and black phosphorus with suitably designed diarylethene (DAE) molecules to modulate their electron and hole transport, respectively, without sacrificing their pristine electrical performance. The efficient and reversible photochemical isomerization of the DAEs between the open and the closed isomer, featuring different energy levels, makes it possible to generate photoswitchable charge trapping levels, resulting in the tuning of charge transport through the 2DMs by alternating illumination with UV and visible light. The device reveals excellent data‐retention capacity combined with multiple and well‐distinguished accessible current levels, paving the way for its use as an active element in multilevel memories.     

Carbon nanotube (CNT)-based composites as electrode material for rechargeable Li-ion batteries: A review

The ever-increasing demands for higher energy density and higher power capacity of Li-ion secondary batteries have led to search for electrode materials whose capacities and performance are better than those available today. Carbon nanotubes (CNTs), because of their unique 1D tubular structure, high electrical and thermal conductivities and extremely large surface area, have been considered as ideal additive materials to improve the electrochemical characteristics of both the anode and cathode of Li-ion batteries with much enhanced energy conversion and storage capacities. Recent development of electrode materials for LIBs has been driven mainly by hybrid nanostructures consisting of Li storage compounds and CNTs. In this paper, recent advances are reviewed of the use of CNTs and the methodologies developed to synthesize CNT-based composites for electrode materials. The physical, transport and electrochemical behaviors of the electrodes made from composites containing CNTs are discussed. The electrochemical performance of LIBs affected by the presence of CNTs in terms of energy and power densities, rate capacity, cyclic life and safety are highlighted in comparison with those without or containing other types of carbonaceous materials. The challenges that remain in using CNTs and CNT-based composites, as well as the prospects for exploiting them in the future are discussed.     

Supramolecular Energy Materials

Self-assembly is a bioinspired strategy to craft materials for renewable and clean energy technologies. In plants, the alignment and assembly of the light-harvesting protein machinery in the green leaf optimize the ability to efficiently convert light from the sun to form chemical bonds. In artificial systems, strategies based on self-assembly using noncovalent interactions offer the possibility to mimic this functional correlation among molecules to optimize photocatalysis, photovoltaics, and energy storage. One of the long-term objectives of the field described here as supramolecular energy materials is to learn how to design soft materials containing light-harvesting assemblies and catalysts to generate fuels and useful chemicals. Supramolecular energy materials also hold great potential in the design of systems for photovoltaics in which intermolecular interactions in self-assembled structures, for example, in electron donor and acceptor phases, maximize charge transport and avoid exciton recombination. Possible pathways to integrate organic and inorganic structures by templating strategies and electrodeposition to create materials relevant to energy challenges including photoconductors and supercapacitors are also described. The final topic discussed is the synthesis of hybrid perovskites in which organic molecules are used to modify both structure and functions, which may include chemical stability, photovoltaics, and light emission.     

Doping Regulation in Polyanionic Compounds for Advanced Sodium-Ion Batteries

It has long been the goal to develop rechargeable batteries with low cost and long cycling life. Polyanionic compounds offer attractive advantages of robust frameworks, long-term stability, and cost-effectiveness, making them ideal candidates as electrode materials for grid-scale energy storage systems. In the past few years, various polyanionic electrodes have been synthesized and developed for sodium storage. Specifically, doping regulation including cation and anion doping has shown a great effect in tailoring the structures of polyanionic electrodes to achieve extraordinary electrochemical performance. In this review, recent progress in doping regulation in polyanionic compounds as electrode materials for sodium-ion batteries (SIBs) is summarized, and their underlying mechanisms in improving electrochemical properties are discussed. Moreover, challenges and prospects for the design of advanced polyanionic compounds for SIBs are put forward. It is anticipated that further versatile strategies in developing high-performance electrode materials for advanced energy storage devices can be inspired.     

Modern synthesis strategies for hierarchical zeolites: Bottom-up versus top-down strategies

Zeolites are well known for their ordered microporous networks, good hydrothermal stability, large surface area, high acidity and selectivity. These excellent properties make zeolites extremely useful for petrochemical processes and refining. However, the presence of only microporous channels also restricts the diffusion of reactants and products into and out of the microporous networks, especially limiting zeolite applications involving bulky molecules. The importance of developing hierarchical zeolites has attracted great attention in recent years due to the prospect of increased accessibility for bulky molecules. Introducing additional mesoporosity, and even macroporosity, into conventional zeolites produces a combination of three different size scales of porosity. It expands the original zeolite hierarchical structure and greatly enhances the mass transport of molecules while maintaining the intrinsic size, shape and transition state selectivity of zeolite. The promising applications of this new zeolite architecture have prompted a multitude of efforts to develop a variety of different synthesis strategies. In this review, we summarized and evaluated the modern synthesis strategies (bottom-up and top-down) for introducing additional meso/macroporosity into microporous zeolites. The advantages and limitations of these different strategies were discussed in detail.     

Layer type tungsten dichalcogenide compounds: their preparation,structure, properties and uses

Tungsten dichalcogenides constitute a well defined family of compounds which crystallize in a layer type structure. These compounds find a wide range of applications in the field of catalysis and as a lubricant at high temperatures and pressures. They have also been investigated successfully as cathode and anode materials in photoelectrochemical cells for solar energy conversion. The layered tungsten dichalcogenides also exhibit superconducting behaviour when intercalated with alkali or alkaline earth metals and different divalent rare earth metals. In the present paper an attempt has been made to review the preparation, crystal structure and band models of tungsten dichalcogenides. Furthermore, we have tried to incorporate the physical, chemical, optical and electrical properties along with intercalation, thermal stability and uses of these compounds.     

Application of electroreflectance analysis for organic semiconductor thin films

Many organic semiconductors with conjugate bond structure possess photoconductivity. Conduction mechanism of organic materials exhibits ‘dualism’ since both intramolecular as well as inter-molecular aspects are involved in the excitation, absorption and transport of charge carriers. Modulation spectroscopy promises to be the most accurate method for analysis of organic photoconductors, especially of thin films. In this technique a periodic perturbation is applied to the material under study and the effect of the perturbation is separated from reflection or absorption while scanning through a given wavelength range by use of lock-in phase sensitive detection method. In electromodulation, particularly in electrolyte electromodulation, the applied field on the material produces changes in the dielectric function which corresponds to the change in reflectance. When the applied field is low the line-shape of spectrum is third-derivative like in comparison with the unmodulated reflectance spectrum. Using Aspnes three-point method the transitions corresponding to critical points can be determined. When the field is intermediate Franz-Keldysh oscillations, which are dc bias dependent, appear on the higher energy side of the transition energy from which the role of intra-molecular as well as intermolecular aspects in conduction mechanism can be understood and the carrier concentration could be determined. Though the electroreflectance method has been developed for inorganic semiconductors, it could be effectively applied for organic/molecular semiconductors as well if the constituent molecules are assumed to be the lattices. The study of organic photoconductors is very important since they are more and more promising especially in photocopying, photovoltaic and solar cells.     

Nanoscale Engineering of Heterostructured Anode Materials for Boosting Lithium‐Ion Storage

Rechargeable lithium‐ion batteries (LIBs), as one of the most important electrochemical energy‐storage devices, currently provide the dominant power source for a range of devices, including portable electronic devices and electric vehicles, due to their high energy and power densities. The interest in exploring new electrode materials for LIBs has been drastically increasing due to the surging demands for clean energy. However, the challenging issues essential to the development of electrode materials are their low lithium capacity, poor rate ability, and low cycling stability, which strongly limit their practical applications. Recent remarkable advances in material science and nanotechnology enable rational design of heterostructured nanomaterials with optimized composition and fine nanostructure, providing new opportunities for enhancing electrochemical performance. Here, the progress as to how to design new types of heterostructured anode materials for enhancing LIBs is reviewed, in the terms of capacity, rate ability, and cycling stability: i) carbon‐nanomaterials‐supported heterostructured anode materials; ii) conducting‐polymer‐coated electrode materials; iii) inorganic transition‐metal compounds with core@shell structures; and iv) combined strategies to novel heterostructures. By applying different strategies, nanoscale heterostructured anode materials with reduced size, large surfaces area, enhanced electronic conductivity, structural stability, and fast electron and ion transport, are explored for boosting LIBs in terms of high capacity, long cycling lifespan, and high rate durability. Finally, the challenges and perspectives of future materials design for high‐performance LIB anodes are considered. The strategies discussed here not only provide promising electrode materials for energy storage, but also offer opportunities in being extended for making a variety of novel heterostructured nanomaterials for practical renewable energy applications.     

Thermoelectricity in fullerene-metal heterojunctions

Thermoelectricty in heterojunctions, where a single-molecule is trapped between metal electrodes, has been used to understand transport properties at organic-inorganic interfaces. (1) The transport in these systems is highly dependent on the energy level alignment between the molecular orbitals and the Fermi level (or work function) of the metal contacts. To date, the majority of single-molecule measurements have focused on simple small molecules where transport is dominated through the highest occupied molecular orbital. (2, 3) In these systems, energy level alignment is limited by the absence of electrode materials with low Fermi levels (i.e., large work functions). Alternatively, more controllable alignment between molecular orbitals and the Fermi level can be achieved with molecules whose transport is dominated by the lowest unoccupied molecular orbital (LUMO) because of readily available metals with lower work functions. Herein, we report molecular junction thermoelectric measurements of fullerene molecules (i.e., C(60), PCBM, and C(70)) trapped between metallic electrodes (i.e., Pt, Au, Ag). Fullerene junctions demonstrate the first strongly n-type molecular thermopower corresponding to transport through the LUMO, and the highest measured magnitude of molecular thermopower to date. While the electronic conductance of fullerenes is highly variable, due to fullerene's variable bonding geometries with the electrodes, the thermopower shows predictable trends based on the alignment of the LUMO with the work function of the electrodes. Both the magnitude and trend of the thermopower suggest that heterostructuring organic and inorganic materials at the nanoscale can further enhance thermoelectric performance, therein providing a new pathway for designing thermoelectric materials.