Organic Host Materials for Solution-Processed Phosphorescent Organic Light-Emitting Diodes

As a new technology for flat-panel displays and general lighting sources, solution-processed phosphorescent organic light-emitting diodes (PhOLEDs) unfurl a bright future, due to their merits of high quantum efficiency and easy fabrication. In recent years, great progress has been made in the device performance of solution-processed PhOLEDs, by developing both high-efficiency organometallic phosphors and novel solution-processable organic host materials. This review highlights recently developed organic host materials for triplet guest emitters in solution-processed PhOLEDs. The solution-processable host materials are classified into three types – small molecule, dendrimer, and polymer – according to their molecular architecture and molecular weight. The material design concept and the relationships between the molecular structure, material properties and device performance are the focus of this discussion. A future strategy for the development of high-performance solution-processed host materials is proposed.     

Recent Advances in Solid-State White Light-Emitting Electrochemical Cells

Compared to organic light-emitting diodes, solid-state light-emitting electrochemical cells (LECs) exhibit advantages of simple device structures, low operation voltages, and compatibility with air-stable metal electrodes. Since the first demonstration of white LECs in 1997, the cells have been studied extensively, due to their potential applications in solid-state lighting. This article reviews the development of white LECs based on conjugated polymers and cationic transition metal complexes. Important achievements of each work on white LECs are highlighted. Finally, the outlook for future development of white LECs is discussed.     

白色有机电致发光材料与器件

综述白色有机电致发光材料和器件的研究进展。归纳了获取白色有机电致发光的途径和方法。分析了多种器件结构的特点及其材料。结合研究过程中存在的某些问题,从器件的发光效率和色纯度角度,讨论了影响发光器件性能的诸因素及其改进措施。     

Theoretical investigation on the white-light emission from a single-polymer system with simultaneous blue and orange emission

White organic light-emitting devices (WOLEDs) have attracted considerable attention because of their good potential for various lighting applications. Among these devices, WOLEDs based on polymers (WPLEDs) are of particular interest. We report here a theoretical investigation of the white-light emission from a single-polymer system with simultaneous blue (polyfluorene as a blue host) and orange (2,1,3-benzothiadiazole-based derivative as an orange dopant) emission. A variety of theoretical methods are used and evaluated to calculate electronic and optical properties of polyfluorene and 2,1,3-benzothiadiazole-based derivatives. Simulated electronic and optical properties are found to agree well with available experimental measurements. The influence of the “CH”/N heterosubstitution on the electronic and optical properties of the 2,1,3-benzothiadiazole-based derivative is considered. Furthermore, we find that the electronic and optical properties of “CH”/N substitution derivatives can be tuned by symmetrically adding suitable electron-donating groups on N,N-disubstituted amino groups, implying good candidates as orange dopants in WPLEDs with polyfluorene as a blue-light-emitting host. Solvent (dichloromethane) effects on the electronic and optical properties of 2,1,3-benzothiadiazole-based derivatives have been investigated. In addition, low reorganization energy values of holes for designed 2,1,3-benzothiadiazole-based derivatives within the framework of the charge hopping model suggest them to be good hole transfer materials.     

Light-emitting devices for wearable flexible displays

Light-emitting devices have potential applications in functional and 'intelligent' textiles and clothing. Much research work has been conducted on electroluminescent devices based on small organic molecules and polymers due to their potential application in new generation displays. An overview is presented of progress in the development of organic and polymer light-emitting devices. The fabrication processes, materials and methods of improving their performance are reviewed. Attention is given to the potential application of flexible displays and the patterning method for producing a full colour display. Analytical methods are also discussed.     

Color stability and suppressed efficiency roll-off in white organic light-emitting diodes through management of interlayer and host properties

Color stability and efficiency roll-off of white light-emitting diodes (WOLEDs) with blue fluorescent and red phosphorescent emitting materials were manipulated by controlling the charge transport properties of interlayer and triplet host materials. A pure white emission was observed in WOLEDs with a bipolar interlayer and a hole transport type triplet host material. A white color coordinate of (0.31, 0.35) and a current efficiency of 14.4 cd/A were obtained. In addition, color index of WOLEDs could be kept stable up to a high luminance of 10,000 cd/m² and an efficiency roll-off was also suppressed.     

Recent Advances in Organometallic Polymers as Highly Efficient Electrophosphorescent Emitters

Recent progress and development of organometallic electrophosphorescent polymers, which attracted increasing interest of researchers in the field of phosphorescent light-emitting devices, has been reviewed. The synthesis, structural characterization, photoluminescence, electroluminescence and possible application of electrophosphorescent polymers are surveyed and discussed. This paper is dedicated to the outstanding scientific accomplishments of Professor Ian Manners to the field of inorganic and organometallic polymers.     

Designing π-conjugated polymers for organic electronics

Conjugated polymers have attracted an increasing amount of attention in recent years for various organic electronic devices because of their potential advantages over inorganic and small-molecule organic semiconductors. Chemists can design and synthesize a variety of conjugated polymers with different architectures and functional moieties to meet the requirements of these organic devices. This review concentrates on five conjugated polymer systems with 1D and 2D topological structures, and on one polymer designing approach. This includes (i) conjugated polyphenylenes (polyfluorenes, polycarbazoles, and various stepladder polymers), (ii) other polycyclic aromatic hydrocarbons (PAHs) as substructures of conjugated polymers, (iii) thiophene and fused thiophene containing conjugated polymers, (iv) conjugated macrocycles, (v) graphene nanoribbons, and finally (vi) a design approach, the alternating donor–acceptor (D–A) copolymers. By summarizing the performances of the different classes of conjugated polymers in devices such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and polymer solar cells (PSCs), the correlation of polymer structure and device property, as well as the remaining challenges, will be highlighted for each class separately. Finally, we summarize the current progress for conjugated polymers and propose future research opportunities to improve their performance in this exciting research field.     

Optimization of opto‐electronic property and device efficiency of polyfluorenes by tuning structure and morphology

Polyfluorene‐based oligomers and polymers (PFs) have been studied intensively as active materials for organic optoelectronic devices. In this review, the optimization of the opto‐electronic property and device efficiency of polyfluorenes in the field of light‐emitting diodes (LEDs) and photovoltaic cells (PVs) by tuning structure and morphology are summarized in terms of two typical modification techniques: copolymerization and blending. The relationships between molecular structures, thin film morphologies, opto‐electronic properties and device efficiencies are discussed, and some recent progress in LEDs and PVs is simultaneously reviewed. After the introduction, the basic knowledge of molecular structures and properties of polyfluorene homopolymers is presented as a background for a better understanding of their great potential for opto‐electronic applications. Immediately after this, three different opinions on the origin of low‐energy emission band at 520–540 nm in polyfluorene‐based LEDs are addressed. Rod–coil block copolymers and alternative copolymers are focused on in the next section, which are a vivid embodiment of controlling supramolecular structures and tailoring molecular structures, respectively. In particular, various supramolecular architectures induced by altering coil blocks are carefully discussed. Recent work that shows great improvement in opto‐electronic properties or device performance by blending or doping is also addressed. Additionally, the progress of understanding concerning the mechanisms of exciton dynamics is briefly referred to. Copyright © 2006 Society of Chemical Industry     

Recent advances in conjugated polymers for light emitting devices

A recent advance in the field of light emitting polymers has been the discovery of electroluminescent conjugated polymers, that is, kind of fluorescent polymers that emit light when excited by the flow of an electric current. These new generation fluorescent materials may now challenge the domination by inorganic semiconductor materials of the commercial market in light-emitting devices such as light-emitting diodes (LED) and polymer laser devices. This review provides information on unique properties of conjugated polymers and how they have been optimized to generate these properties. The review is organized in three sections focusing on the major advances in light emitting materials, recent literature survey and understanding the desirable properties as well as modern solid state lighting and displays. Recently, developed conjugated polymers are also functioning as roll-up displays for computers and mobile phones, flexible solar panels for power portable equipment as well as organic light emitting diodes in displays, in which television screens, luminous traffic, information signs, and light-emitting wallpaper in homes are also expected to broaden the use of conjugated polymers as light emitting polymers. The purpose of this review paper is to examine conjugated polymers in light emitting diodes (LEDs) in addition to organic solid state laser. Furthermore, since conjugated polymers have been approved as light-emitting organic materials similar to inorganic semiconductors, it is clear to motivate these organic light-emitting devices (OLEDs) and organic lasers for modern lighting in terms of energy saving ability. In addition, future aspects of conjugated polymers in LEDs were also highlighted in this review.     

倍半硅氧烷基电致发光材料的研究进展

有机电致发光器件(OLED)作为一种新型显示器件,其结构简单、易于制造、成本更低、性能更好,未来在各领域将有很大的应用潜力。其中电致发光材料是OLED的核心材料,是OLED能否工业化生产的关键因素,但目前发光材料仍存在一些不足。多面体倍半硅氧烷(POSS)作为一种笼状无机材料,由于具有良好的耐热性、力学强度、稀释效应,经常与咔唑、芴等有机物杂化,从而有效地改善光电和物理性能,被用作OLED电致发光材料,已得到当前电致发光研发领域的极大关注。本文主要介绍了倍半硅氧烷基电致发光材料的研究进展。     

窄带隙共轭聚合物/富勒烯衍生物光探测器件的研究

基于高灵敏度、宽光谱响应的窄带隙共轭聚合物光探测器件的研究取得了突破性进展,受到了学术界和产业界的高度重视,成为了当前光探测器件研究的热点课题之一.本文概述了窄带隙共轭聚合物作为电子给体与电子受体PC61BM下光伏器件的研究进展及存在的问题.提出了带隙更窄、光谱响应更宽的共轭聚合物的合成与器件的优化研究将具有更大的发展...     

The influence of type-I and type-II triplet multiple quantum well structure on white organic light-emitting diodes

We demonstrate high-efficient white organic light-emitting diodes (WOLEDs) based on triplet multiple quantum well (MQW) structure and focus on the influence on WOLEDs through employing different potential barrier materials to form type-I and type-II MQWs, respectively. It is found that type-I MQW structure WOLEDs based on 1,3,5-tris(N-phenyl-benzimidazol-2-yl)benzene as potential barrier layer (PBL) offers high electroluminescent (EL) performance. That is to say, maximum current efficiency and power efficiency are achieved at about 1,000 cd/m² with 16.4 cd/A and 8.3 lm/W, which increase by 53.3% and 50.9% over traditional three-layer structure WOLEDs, respectively, and a maximum luminance of 17,700 cd/m² is earned simultaneously. The achievement of high EL performance would be attributed to uniform distribution and better confinement of carriers within the emitting layer (EML). However, when 4,7-diphenyl-1,10-phenanthroline or 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline is used as PBL to form type-II MQW structure, poor EL performance is obtained. We attribute that to improper energy level alignment between the interface of EML/PBL, which leads to incomplete confinement and low recombination efficiency of carriers, a more detailed mechanism was argued.     

Fluorinated conjugated polymers in organic bulk heterojunction photovoltaic solar cells

The photovoltaic technology represents a major renewable energy source to harnes the solar power. Over the last two decades, the development of solution-processed bulk heterojunction polymer solar cells has attracted a considerable interest. This has resulted in a significant efficiency improvement through innovation of device architectures and molecular structure design of donor polymers. In this regard, the introduction of fluorinated units along the conjugated backbone has emerged as a successful strategy for further fine-tuning the physical and chemical properties of conducting polymers. In this review, we highlight recent strategies aiming at improving the solar cell performance by variable fluorine substitution of repeating units. Fluorination was found to achieve a modulation of HOMO and LUMO energy levels and optical properties to some extent. Moreover, intermolecular interactions involving fluorine atoms have a significant influence on blend film morphology. The resulting organic photovoltaic solar cells endowed some of the highest power conversion efficiency values reported to date.     

Blue Fluorescence and Bipolar Transport Materials Based on Anthracene and Their Application in OLEDs

The phenomenon of organic electroluminescence (EL) was first discovered from studies on anthracene crystals in the 1960s. Since then, its derivatives have been studied extensively in applications such as organic light-emitting diodes (OLEDs) and organic thin-film transistors because of their excellent EL, transport, and good electrochemical properties. A blue fluorescence emitter based on anthracene is also important in constructing hybrid tandem white OLEDs for lighting applications. This article provides a review about the development of blue host OLED materials based on molecules designed and derived from the core structure of anthracene and their application as bipolar charge-carrier transport materials in OLEDs. The recent development of efficient, stable, blue-doped p-i-n OLEDs with simplified device architecture based on the single common host 2-methyl-9,10-di(2-napthyl)anthracene, with its stable thin-film morphology, large band gap energy, high fluorescence quantum yield, and ambipolar charge-carrier transport properties, is also highlighted.     

Survey on Langmuir–Blodgett Films of Polymer and Polymeric Composite

This article presents a concise review of research performed in the field of Langmuir–Blodgett films. Various types of conducting polymers, piezoelectric/pyroelectric polymers, and ferroelectric polymers have been utilized for fabrication of polymeric and composite Langmuir–Blodgett films. The Langmuir–Blodgett polymers may reveal fine Langmuir–Blodgett behavior such as mechanical robustness, heat resistance, and chemical stability. Moreover, polymers offer recompenses of synthetic tailoring, low-cost, and volume production toward enhanced performance Langmuir–Blodgett materials. The applications of Langmuir–Blodgett films have been reviewed in sensors, electroluminescence devices, polymeric light-emitting diode, and microelectronic devices. Langmuir–Blodgett films represent exciting area of materials science demanding recent research attention.     

Phosphonate-functionalized polyfluorene and its application in organic optoelectronic devices

Conjugated polar polymers, in which the conjugated backbones are chemically anchored with functional polar side groups, can be processed with water/alcohol solvents, and thus multilayered device architectures can be easily realized via sequential solution processing of the toluene-soluble emissive polymer and alcohol-soluble electron-transporting polymer without intermixing. Regarding their use in organic optoelectronic devices, the success in achieving efficient charge injection and intimate contact between metal electrodes and organic semiconductors is very vital for enhancing the device performance. In this short review, it gives a brief review to neutral alcohol-soluble phosphonate-functionalized polyfluorene, mainly concerning the electronic structure at the phosphonate-functionalized polyfluorene/aluminum cathode interface and its successful application in multilayered polymer optoelectronic devices including polymer light-emitting diodes and polymer solar cells.     

Novel optoelectronic devices based on single semiconductor nanowires (nanobelts)

ABSTRACT: Semiconductor nanowires (NWs) or nanobelts (NBs) have attracted more and more attention due to their potential application in novel optoelectronic devices. In this review, we present our recent work on novel NB photodetectors, where a three-terminal metal-semiconductor field-effect transistor (MESFET) device structure was exploited. In contrast to the common two-terminal NB (NW) photodetectors, the MESFET-based photodetector can make a balance among overall performance parameters, which is desired for practical device applications. We also present our recent work on graphene nanoribbon/semiconductor NW (SNW) heterojunction light-emitting diodes (LEDs). Herein, by taking advantage of both graphene and SNWs, we have fabricated, for the first time, the graphene-based nano-LEDs. This achievement opens a new avenue for developing graphene-based nano-electroluminescence devices. Moreover, the novel graphene/SNW hybrid devices can also find use in other applications, such as high-sensitivity sensor and transparent flexible devices in the future.     

Light-emitting devices with conjugated polymers

This article introduces a previous study and tremendous progress in basic theoretical modeling, material developments and device engineering for polymer light-emitting devices (PLEDs).     

Vacuum-deposited perovskite CsPbBr3 thin-films for temperature-stable Si based pure-green all-inorganic light-emitting diodes

Metal halide perovskite light-emitting diodes (PeLEDs) are excellent candidates in the field of lighting and display due to their outstanding optical-electrical properties. However, the solution-processed technology of perovskite films and the organic electron/hole transport layers of PeLEDs make it still challenging to improve the operational stability of devices. Herein, we successfully prepared highly luminescent CsPbBr₃ perovskite films via vacuum-deposited method and then fabricated all-inorganic PeLEDs with the heterostructure of p-NiO/CsPbBr₃/n-Si. Our device exhibits pure-green emission with a wavelength of 527 nm, a narrow full width at half-maximum of 18 nm, and a maximum luminance of 51933 cd/m², representing one of the best brightness pure-green PeLEDs. Most importantly, the PeLEDs exhibited great thermal stability with a heat resistance up to 80 °C. The electroluminescence peak position of the PeLEDs remains consistent when the ambient temperature increases from 40 °C to 110 °C. Moreover, the all-inorganic PeLEDs can maintain their good luminescence performance after seven thermal cycling tests (30 °C–100 °C). This work not only demonstrated a facile strategy to prepare high-quality pure-green CsPbBr₃ perovskite films, but also provided an important all-inorganic device structure for high thermal stability of PeLED.