Advancement in materials for energy-saving lighting devices

This review provides a comprehensive account of energy efficient lighting devices, their working principles and the advancement of these materials as an underpinning to the development of technology. Particular attention has been given to solid state lighting devices and their applications since they have attracted the most interest and are the most promising. Solid state lighting devices including white light emitting diodes (LEDs), organic LEDs (OLEDs), quantum-dot LEDs (QLEDs) and carbon-dot LEDs (CLEDs) are promising energy efficient lighting sources for displays and general lighting. However there is no universal solution that will give better performance and efficiency for all types of applications. LEDs are replacing traditional lamps for both general lighting and display applications, whereas OLEDs are finding their own special applications in various areas. QLEDs and CLEDs have advantages such as high quantum yields, narrow emission spectra, tunable emission spectra and good stability over OLEDs, so applications for these devices are being extended to new types of lighting sources. There is a great deal of research on these materials and their processing technologies and the commercial viability of these technologies appears strong.     

Recent advances in transistor performance of polythiophenes

Polythiophenes have long played a major role in the field of conducting polymers due to their relative ease of synthesis, good thermal and oxidative stability, high charge carrier mobility and ease of processing and they have found widespread use in electronic applications such as field-effect transistors (FETs), organic photovoltaics (OPVs), light-emitting diodes (LEDs) and electrochromic displays (ECDs). In this review, we summarize the most important synthetic approaches to thiophene-, thienothiophene- and other fused thiophene-based polymers, highlight a number of significant findings relating to their properties with an emphasis on device performance in organic field-effect transistors and reflect on existing challenges and future opportunities in the field.     

Progress and perspective of iridium-containing phosphorescent polymers for light-emitting diodes

Phosphorescent polymer light-emitting diodes (PhPLEDs) have become the subject of intensive investigation due to their promising applications for displays and lighting. This review presents recent progress in single iridium-containing phosphorescent polymers for PhPLEDs according to their different emitting colors. These phosphorescent polymers are further classified as main chain, side chain, and chelating-types based on the manner in which the host and dopant units are connected. The relationship between the polymer structures and electroluminescence properties is the main focus of this review. Finally, some important rules for designing new efficient phosphorescent polymers are discussed.     

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.     

Altering the emission properties of conjugated polymers

Many technological applications that have had tremendous impact on our society and lifestyle are exploiting the emission properties of organic species such as conjugated polymers and organic small‐molecule semiconductors. The most prominent case‐in‐point here are possibly organic light‐emitting diodes, which have found use in information displays, touch screens and beyond. To further advance the rapid development of these powerful and versatile technologies, it will be of paramount importance to gain fundamental insights about which strategies and processes we can employ to alter, control and eventually enhance the emission properties of this interesting class of material. In this work, we focus on macromolecular systems and review the most important categories of tools that can be employed to efficiently alter their emission properties by manipulating their molecular architecture and electronic structure; by influencing their molecular ordering, packing motifs and overall microstructure; as well as by utilizing the ability of some of these materials to respond to external stimuli and other physical parameters (pressure, light exposure etc.) and/or to interact with other compounds, including systems of different functionalities. © 2015 Society of Chemical Industry     

Interface‐tailored and nanoengineered polymeric materials for (opto)electronic devices

For plastic (opto)electronic devices such as light‐emitting diodes (LEDs), photovoltaic (PV) cells and field‐effect transistors (FETs), the processes of charge (hole/electron) injection, charge transport, charge recombination (exciton formation), charge separation (exciton diffusion and dissociation) and charge collection are critical to enhance their performance. Most of these processes are relevant to nanoscale and interfacial phenomena. In this review, we highlight the state‐of‐the‐art developments of interface‐tailored and nanoengineered polymeric materials to optimize the performance of (opto)electronic devices. These include (1) interfacial engineering of anode and cathode for polymer LEDs; (2) nanoengineered (C₆₀ and inorganic semiconductor nanoparticles) π‐conjugated polymeric materials for PV cells; and (3) polymer and monolayer dielectrics/interfaces for FETs and light‐emitting and nano‐FETs. Copyright © 2009 Society of Chemical Industry     

Electroluminescence in Semiconducting Conjugated Polymers and Oligomers: A Quantum-chemical Perspective

Abstract

We discuss in this contribution the ability of quantum-chemical calculations to describe the essential aspects of one of the most promising applications of semiconducting conjugated polymers and oligomers, i.e., their use as active layers in light-emitting diodes (LEDs). We present an overview of the results of recent theoretical studies that we have performed on oligomers representative of polyparaphenylenevinylene and polythio-phene. We mostly deal with: (i) the modelling of the linear optical properties of the conjugated polymers involved in the emitting layer, taking into account the vibronic structure; (ii) the investigation of the relative locations of. and relaxation phenomena taking place in. the lowest singlet and triplet excited states; and (iii) a general discussion of the various terms contributing to the polaron-exciton binding energy.     

Light-emitting transistor structures based on semiconducting polymers and inorganic nanoparticles

One of the new directions in organic electronics is the development of light-emitting organic field-effect transistors, which combine the light-emitting properties of organic light-emitting diodes and the switching properties of organic field-effect transistors. Optical and electronic properties of novel nanocomposite materials based on semiconducting polymers and inorganic nanoparticles and designed for applications in organic electronics devices were investigated. Light-emitting organic field-effect transistors with composite active layers based on the soluble semiconducting polymers PFO and MEH-PPV and ZnO nanoparticles and having asymmetric electrodes (Al and Au) that inject electrons into ZnO and holes into PFO and MEH-PPV were prepared and investigated. The data are interpreted in the context of the possibility of organic field-effect transistors based on PFO: ZnO and MEH-PPV: ZnO composite films to work in both the unipolar regime and the ambipolar regime. It is shown that the mobility of charge carriers in light-emitting organic field-effect transistors based on PFO: ZnO at 300 K reaches ～0.02 for electrons and ～0.03 cm²/(V s) for holes, increasing with an increase in the concentration of nanoparticles up to ～2 cm²/(V s), a value that is comparable to the maximum mobility values for conducting polymers. Light-emitting organic field-effect transistors based on PFO: ZnO and MEH-PPV: ZnO emit light in the green and orange ranges of the optical spectrum, respectively, their electroluminescence intensities rising with an increase in either the negative bias or the positive bias at the source-drain and the gate as well as with an increase in the concentration of ZnO nanoparticles. The results indicate that light-emitting organic field-effect transistors based on soluble conjugated polymers and semiconducting ZnO nanoparticles are examples of multifunctional devices whose production technology is compatible with the modern ink-jet printing technology of organic electronics.     

1989 Polycyclic Aromatic Hydrocarbon Research Award

Organic electroluminescent devices recently have been focus of attention. Since the first demonstrations in this field, rapid developments have occurred in the usage of organic polyaromatic compounds and their derivatives for the purpose of multi-layer structures, multi-color, and full-color organic light-emitting diode displays. In the part-1 of the present short review, recent technical developments in the preparation and structure of organic light emitting diodes with special attention to organic emitters involving polyaromatic kernels have been considered.     

Novel luminescent polymers containing backbone triphenylamine groups and pendant quinoxaline groups

Novel, conjugated polyfluorene derivatives that comprised an electron-donating triphenylamine group in the backbone and pendant, electron-accepting quinoxaline moieties, were synthesized via the Suzuki coupling reaction and their UV–vis absorption, fluorescence emission and electrochemical properties were investigated. The copolymers were readily soluble in common organic solvents and displayed good film-forming ability and excellent thermal stability. Electroluminescence devices, comprising indium tin oxide/poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonic acid)/emitting polymer/Ba/Al, in which the polymers were employed as emissive layers, exhibited superior performance compared to that of corresponding, poly(9,9-dioctylfluorene) and poly(9,9-dioctylfluorene-co-4,4′-triphenylamine) based devices, indicating that the polymers offer promise as emissive materials in polymeric light-emitting diodes.     

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.     

Enhanced electroluminescence from a conjugated polymer/ionomer blend

Poly [2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and poly (sodium 4-styrenesulfonate) ionomer (PSS-ionomer) blends were used as emitting layers in polymer light-emitting diodes (LEDs). The polymers were blended in various ratios, and their luminescent properties were compared with those of a MEH-PPV/polystyrene (PS) blend system. The MEH-PPV/PSS-ionomer and MEH-PPV/PS devices showed a much higher luminescent efficiency when compared with pure polymer devices, due to the dilution effect. The MEH-PPV/PSS-ionomer blend device achieved a more enhanced luminescent efficiency as compared with that of the MEH-PPV/PS device, due to polar groups in the PSS-ionomer, which may enhance the electron injection from the cathode to the emitting molecules. In addition, the turn-on voltage of the MEH-PPV/PSS-ionomer based on LEDs was also dramatically decreased.     

Eco-friendly Mn-doped CsPbCl3 perovskite nanocrystal glass with blue-red emission for indoor plant lighting

Mn-doped CsPbCl₃ perovskite nanocrystal (PeNC) glass was prepared by melt quenching and in situ crystallization. Under the protection of robust glass, PeNCs exhibit excellent moisture resistance and thermal stability. The combination effect of thermal quenching and energy transfer of exciton to Mn²⁺ enables its promising applications in the field of temperature sensor. Interestingly, by matching with ultraviolet chips, all-inorganic blue-red emitting conversion device consisting of PeNC glass was prepared for light-emitting diodes (LEDs), which can meet the light requirements of plant growth. The cultivation results indicated that the growth of cabbages using PeNC plant cultivation LEDs was greater than those cultivated using commercial w-LEDs (white light-emitting diodes). Therefore, Mn-doped CsPbCl₃ PeNCs can be used as a new generation of solid fluorescent materials in the field of indoor plant cultivation LEDs.     

Conjugated polymers/semiconductor nanocrystals hybrid materials--preparation, electrical transport properties and applications

This critical review discusses specific preparation and characterization methods applied to hybrid materials consisting of π-conjugated polymers (or oligomers) and semiconductor nanocrystals. These materials are of great importance in the quickly growing field of hybrid organic/inorganic electronics since they can serve as active components of photovoltaic cells, light emitting diodes, photodetectors and other devices. The electronic energy levels of the organic and inorganic components of the hybrid can be tuned individually and thin hybrid films can be processed using low cost solution based techniques. However, the interface between the hybrid components and the morphology of the hybrid directly influences the generation, separation and transport of charge carriers and those parameters are not easy to control. Therefore a large variety of different approaches for assembling the building blocks--conjugated polymers and semiconductor nanocrystals--has been developed. They range from their simple blending through various grafting procedures to methods exploiting specific non-covalent interactions between both components, induced by their tailor-made functionalization. In the first part of this review, we discuss the preparation of the building blocks (nanocrystals and polymers) and the strategies for their assembly into hybrid materials' thin films. In the second part, we focus on the charge carriers' generation and their transport within the hybrids. Finally, we summarize the performances of solar cells using conjugated polymer/semiconductor nanocrystals hybrids and give perspectives for future developments.     

Design of photonic crystals for light-emitting diodes

Photonic crystals (PCs) can greatly enhance the optoelectronic performance of light-emitting diodes (LEDs) due to their distinctive color, photonic band gap, etc. Therefore, many scholars have conducted extensive research based on the high light extraction efficiency, good monochromaticity, and other excellent optoelectronic properties of PC LEDs. This review discusses the main principles of photonic crystals to improve the optoelectronic performance of LEDs and summarizes 12 structural applications of photonic crystal LEDs, such as PC slabs, Bragg grating, backside reflectors, surface PC, embedded PC, dual PC, PC beads, CPC, PC thin films, LIPC, defective PC, and composite architectures with other materials that boost LED optoelectronic qualities. In summary, it is found that photonic crystals can not only greatly improve the light extraction efficiency of LEDs but also improve other optoelectronic properties such as luminescent color and directional radiation angle, and reduce the manufacturing cost of LEDs. Photonic crystal LEDs are expected to be a strong candidate for future lighting technology. Finally, the prospects and challenges of PC LEDs are summarized.     

Improving the performance of polymer light‐emitting devices with chemical tools

This review presents the strategies that have been employed to build polymer light‐emitting devices as far as the chemical design of fully conjugated polymers and device structure engineering are concerned. In particular, it gives an overview of the wealth of materials used as single emissive layers imagined by chemists in the quest for the improvement of the efficiency of devices with simplified structures. We give selected examples of the efforts made to synthesize materials that can transport both positive and negative charge carriers. The last part is devoted to the attention paid to highly emissive materials with a special focus on single conjugated electro‐phosphorescent polymers. © 2013 Society of Chemical Industry     

Recent Advances in Solution-Processed White Organic Light-Emitting Materials and Devices

Solution-processed white organic light-emitting diodes (WOLEDs) have drawn great attention both in the academic and industrial research communities due to the potential application in low-cost, large-area, solid-state lightings. Issues related to the device efficiencies are largely hampering progress in this field. Alongside the development of new materials and novel device architectures, distinct progress has been made for such white devices. In particular, the all-phosphorescent light-emitting strategy has been intensively developed in recent years, mainly focusing on a host guest, doping-system-based, single-active-layer structure and a solution-processed, multilayer device structure. Novel approaches, including white single polymers and excimer-/exciplex-based white devices, have also appeared as a promising choice and received great attention. As a prerequisite, the issue of the morphology of the emissive layer is also important and has an influence on the optoelectronic behavior of the device. Herein, major advances in solution-processed WOLEDs based on polymers, dendrimers, or solution-processed small molecules are summarized. Special attention is focused on the main progress in high-efficiency, solution-processed WOLEDs with the key strategies mentioned above and the morphology issue in these systems. The remaining challenges in pursuing the development of reliable and energy-saving lighting devices are also discussed.     

苯并噻二唑共轭有机分子合成研究进展

2,1,3-苯并噻二唑(BTD)共轭有机分子具有优异的光电特性,广泛应用于有机发光二极管、太阳能电池、液晶、荧光探针、光电管等方面。综述了以金属催化的偶联反应为关键步骤的2,1,3-苯并噻二唑(BTD)共轭有机分子的合成方法,包括Suzuki偶联反应,Stille偶合反应,Heck偶联反应,Sonogashir偶联反应,Nigishi偶联反应,Ullmann偶联反应等。     

Review of electronic and optical properties of semiconducting π‐conjugated polymers: applications in optoelectronics

A general overview of the optoelectronic properties of π‐conjugated polymers is presented. Two types of polymer are discerned: interchangeable structures of the same energy (degenerate), such as polyacetylene; and non‐degenerate polymers, such as poly(para‐phenylene). The band structures of degenerate and non‐degenerate polymers are related to their conductivities in doped and non‐doped states. In both cases, disorder and impurities play an important role in conductivity. Polarons, bipolarons and excitons are detailed with respect to doping and charge transfers. Given the fibrillic nature of these materials, the variable range hopping (VRH) law for semiconducting polymers is modified to account for metallic behaviours. Optoelectronic properties—electroluminescence and photovoltaic activity—are explained in terms of HOMO and LUMO bands, polaron‐exciton and charge movement over one or more molecules. The properties of H‐ or J‐type aggregates and their effects on transitions are related to target applications. Device structures of polymer light‐emitting diodes are explicitly linked to optimising polaron recombinations and overall quantum efficiencies. The particularly promising use of π‐conjugated polymers in photovoltaic devices is discussed. Copyright © 2004 Society of Chemical Industry     

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