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     

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.     

Controlling Polymer Solubility: Polyfluorenes with Branched Semiperfluorinated Side Chains for Polymer Light-Emitting Diodes

A series of novel polyfluorenes, soluble exclusively in perfluorinated solvents, were prepared. The new materials were studied with regard to orthogonal processing of organic electronic materials. The desired solubility was achieved by introducing semifluorinated side chains to the fluorene monomers. Since the use of long perfluoroalkyl chains (R^F) is restricted due to public health concerns, a synthetic route for polyfluorenes with short R^F chains branched by aromatic units has been developed. The photophysical behavior of the resulting polymers was investigated in solution and thin films by UV/Vis absorption and photoluminescence spectroscopy. The photoluminescence quantum yields were found to be in the range of those of alkylated polyfluorenes. The electroluminescent properties were studied in single-layer polymer light-emitting diodes, with the new polymers as active materials, which exhibited similar characteristics to previously published single-layer devices with polyfluorenes containing long R^F. The wetting properties of different polyfluorene films containing fluorinated, polar, polyethylene glycol, or nonpolar alkyl groups were investigated by contact angle measurements.     

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.     

Electronic Structures of S-Doped Capped C-SWNT from First Principles Study

The semiconducting single-walled carbon nanotube (C-SWNT) has been synthesized by S-doping, and they have extensive potential application in electronic devices. We investigated the electronic structures of S-doped capped (5, 5) C-SWNT with different doping position using first principles calculations. It is found that the electronic structures influence strongly on the workfunction without and with external electric field. It is considered that the extended wave functions at the sidewall of the tube favor for the emission properties. With the S-doping into the C-SWNT, the HOMO and LUMO charges distribution is mainly more localized at the sidewall of the tube and the presence of the unsaturated dangling bond, which are believed to enhance workfunction. When external electric field is applied, the coupled states with mixture of localized and extended states are presented at the cap, which provide the lower workfunction. In addition, the wave functions close to the cap have flowed to the cap as coupled states and to the sidewall of the tube mainly as extended states, which results in the larger workfunction. It is concluded that the S-doped C-SWNT is not incentive to be applied in field emitter fabrication. The results are also helpful to understand and interpret the application in other electronic devices.     

工业建筑防雷系统剖析

随着工业控制系统内电子设备的数量和规模不断扩大,而电子设备普遍存在着绝缘强度低,过电压耐受能力差的弱点,当其因雷击受到电磁脉冲,特别是闪电电磁脉冲的袭击,会出现不同程度的运行故障．甚至造成巨大损失。因此工业建筑中的电子设备应进行多级分流（不少于三级防雷保护）的防雷措施．确保生产装置安、稳、优地运行。     

Organic materials for organic electronic devices

In recent years, organic electronic devices which use organic materials as an active layer have gained considerable interest as light-emitting devices, energy converting devices and switching devices in many applications. In these organic electronic devices, the organic materials play a key role of managing the device performances and various organic materials have been developed to improve the device performances of organic electronic devices. In this paper, recent developments of organic electronic materials for organic light-emitting diodes and organic solar cells were reviewed.     

Recent advances and prospect of cobalt based microwave absorbing materials

With the advances and extensive application of electromagnetic (EM) waves in electronic and communication devices. EM pollution has been identified as a threat to human health whereby EM interference also affects the proper functioning of electronic devices. Therefore, the fabrication of novel microwave absorbing materials (MAMs) has become important to mitigate EM pollution and protect humans as well as other nearby electronic devices. The use of sole cobalt as MAM has gained significant attention due to its EM properties and suitable saturation magnetization. However, large density, eddy current loss, and poor corrosion resistance are some of the factors that hinder its practical application as an ideal MAMs. In this paper, recent advances towards overcoming these challenges have been reviewed. In particular, ways of regulating the morphology and optimizing the EM properties of cobalt-based MAM. Furthermore, fabrication of high-performance lightweight absorbers with hierarchical structures and formation of cobalt-based hybrid MAM with other lossy materials are discussed. Several factors affecting the microwave absorption performance of cobalt-based MAM are further discussed. Finally, the present limitations as well as prospects are put forward to give a new insight into the design of improved cobalt-based MAM.     

A Novel Polymeric Substrate with Dual-Porous Structures for High-Performance Inkjet-Printed Flexible Electronic Devices

Inkjet printing has emerged as a promising low-cost and high-performance method for manufacturing printing-based devices. However, the development of optimized substrates for inkjet printing using novel materials is limited. In this study, a novel polymeric substrate optimized for flexible electronic devices is fabricated using thin-film processing and phase inversion of polyethersulfone (PES). The PES film consists of two layers of pores; the upper layer has nano-sized pores that filter the nanoparticles in the conductive ink and allow for high-density aggregation on the substrate, while the lower layer contains micro-scale pores that quickly absorb and drain the ink solvent. The two porous structures lead to higher conductivity and high-resolution printed patterns by minimizing solvent lateral diffusion. Additionally, the PES printing substrate can undergo high-temperature curing of metal nanoparticles, enabling high-resolution pattern printing with low resistance. The PES substrate is highly transparent and flexible, allowing for the fabrication of various printed electronic patterns and the production of high-performance flexible electronic devices.     

Nanographenes as active components of single-molecule electronics and how a scanning tunneling microscope puts them to work

Single-molecule electronics, that is, realizing novel electronic functionalities from single (or very few) molecules, holds promise for application in various technologies, including signal processing and sensing. Nanographenes, which are extended polycyclic aromatic hydrocarbons (PAHs), are highly attractive subjects for studies of single-molecule electronics because the electronic properties of their flat conjugated systems can be varied dramatically through synthetic modification of their sizes and topologies. Single nanographenes provide high tunneling currents when adsorbed flat onto conducting substrates, such as graphite. Because of their chemical inertness, nanographenes interact only weakly with these substrates, thereby preventing the need for special epitaxial structure matching. Instead, self-assembly at the interface between a conducting solid, such as the basal plane of graphite, and a nanographene solution generally leads to highly ordered monolayers. Scanning tunneling spectroscopy (STS) allows the current-voltage characteristics to be measured through a single molecule positioned between two electrodes; the key to the success of STS is the ability to position the scanning tunneling microscopy (STM) tip freely with respect to the molecule in all dimensions, that is, both parallel and perpendicular to the surface. In this Account, we report the properties of nanographenes having sizes ranging from 0.7 to 3.1 nm and exhibiting various symmetry, periphery, and substitution types. The size of the aromatic system and the nature of its perimeter are two essential features affecting its HOMO-LUMO gap and charge carrier mobility in the condensed phase. Moreover, the extended pi area of larger substituted PAHs improves the degree of self-ordering, another key requirement for high-performance electronic devices. Self-assembly at the interface between an organic solution and the basal plane of graphite allows deposition of single molecules within the well-defined environment of a molecular monolayer. We have used STM and STS to investigate both the structures and electronic properties of these single molecules in situ. Indeed, we have observed key electronic functions, rectification and current control through single molecules, within a prototypical chemical field-effect transistor at ambient temperature. The combination of nanographenes and STM/STS, with the PAHs self-assembled in oriented molecular mono- or bilayers at the interface between an organic solution and the basal plane of graphite and contacted by the STM tip, is a simple, reliable, and versatile system for developing the fundamental concepts of molecular electronics. Our future targets include fast reversible molecular switches and complex molecular electronic devices coupled together from several single-molecule systems.     

Biomaterials‐based organic electronic devices

Organic electronic devices have demonstrated tremendous versatility in a wide range of applications including consumer electronics, photovoltaics and biotechnology. The traditional interface of organic electronics with biology, biotechnology and medicine occurs in the general field of sensing biological phenomena. For example, the fabrication of hybrid electronic structures using both organic semiconductors and bioactive molecules has led to enhancements in the sensitivity and specificity within biosensing platforms, which in turn has a potentially wide range of clinical applications. However, the interface of biomolecules and organic semiconductors has also recently explored the potential use of natural and synthetic biomaterials as structural components of electronic devices. The fabrication of electronically active systems using biomaterials‐based components has the potential to produce a large set of unique devices including environmentally biodegradable systems and bioresorbable temporary medical devices. This article reviews recent advances in the implementation of biomaterials as structural components in organic electronic devices with a focus on potential applications in biotechnology and medicine. Copyright © 2010 Society of Chemical Industry     

New directions in structuring and electrochemical applications of boron-doped diamond thin films

Conductive boron-doped diamond electrodes have been shown to be highly suitable as electrochemical detectors in flow injection analysis and high performance liquid chromatographic analysis, achieving high sensitivity and stability for certain species that cannot be detected at other electrodes due to electrode deactivation or high electrochemical oxidation potential. The use of this electrode material for the detection of chlorophenols and theophylline is demonstrated. Apart from the electrochemistry of diamond, various methods have been developed to fabricate well-aligned nanocylindrical diamond films and periodic bulb-like structures, which may be useful for sensors and electronic devices such as field emission displays.     

Enhanced thermal performance of hybrid interface materials supported by 3D thermally conductive SiC framework

The rapid development of microelectronic integration technology is placing increasing demands on the safety performance of electronic devices. Excellent thermal interface materials (TIM) facilitate the dissipation of heat from electronic components, which ensures the safety of electronic equipment. In this work, a three-dimensional (3D) thermally conductive framework is constructed from carbon fibers to form silicon carbide (SiC) in situ. This is followed by vacuum impregnation with paraffin wax (PW) to produce phase change composites (PCCs). The results show that the SiC-based 3D thermally conductive framework has a hierarchical porous network structure, and the PCC indicates enhanced thermal conductivity and good anti-leakage properties. The thermal conductivity of PW @ CF1–Si1-1550 is 0.81 W K⁻¹m⁻¹, which is 4 times that of PW. In addition, the PCC also shows good thermal cycling properties, high thermal storage capacity (179.06 Jg^-1), and good insulation properties. The PCC as described in this paper as TIM have considerable application potential in thermal management.     

Hydrothermal synthesis of tellurium nanorods by using recovered tellurium from waste electronic devices

Tellurium (Te) nanostructures with controlled morphology have received the considerable attention in various applications owing to tunable optic, thermoelectric, photoelectronic, piezoelectric, and electrochemical properties. Herein, we introduce the cost-effective and eco-friendly synthesis of Te nanorods (Te NRs) from end of life electronic devices via hydrothermal methods. The Te NRs show the average diameter of 44.6?nm and a length of 358?nm in presence of polyvinylpyrrolidone, as a stabilizing agent. Moreover, the bismuth and intact p-type semiconductor (i.e., Bi_0.5Sb_1.5Te₃) are selectively recovered as intermediated products. The Te NRs exhibit the NO₂ gas sensing properties with concentration as low as 1?ppm at room temperature and fast response/recovery times of 1.59 and 2.10?s at 1?ppm, respectively. We believe that this powerful approach can be expanded to not only selective recovery of valuable materials but synthesis of various nanomaterials from waste electronic devices.     

Failure Analysis of Modern Silicon Dice

Although the utilization of silicon dice in electronic devices has been in place for approximately 50 years, its widespread application has occurred more recently with the rapid expansion of the consumer markets for digital devices such as cameras, personal computers, video players, and smart phones. In particular, due to the recent market drive in the miniaturization and cost reduction of electronic products, silicon dice are often utilized without encapsulation and mounted directly to the substrate by means of conductive adhesives or BGA mounting. Silicon die often need to be thinned to a few hundred micrometers thickness to fit into compact devices and to reduce parasitics. The intrinsic brittle nature of silicon in combination with the lack of mechanical protection such as encapsulation has made fracture of bare dice a typical failure mechanism in handheld electronic devices. In the current work, we tested to failure {100} silicon dice and obtained mirror–mist boundary measurements for correlation to the fracture strengths of the parts. This work will also present various practical examples of how to reliably conduct failure analysis of fractured silicon dice. The intrinsic brittle nature of silicon in combination with the lack of mechanical protection such as encapsulation has made fracture of bare dice a typical failure mechanism in handheld electronic devices such as cameras, portable computers, tablets, media players, and smart phones. In these products, silicon dice are often utilized without encapsulation and are attached directly to the substrate by means of conductive adhesives or ball grid array mounting. Modern silicon dice used in these products typically have small dimensions and higher flexural strength compared to their predecessors. Prior silicon fractographic findings have investigated low strength failures. In the current work, we extend the quantitative fractography of silicon to the high failure stress regime. We have mechanically tested modern silicon dice to failure by four‐point bending and obtained mirror–mist boundary measurements for correlation to the fracture strengths of the specimens. Two key areas are addressed which improve the practical application of quantitative fractography to modern silicon dice: (1) application of silicon fractography to high flexural strength regimes and (2) development of a systematic means of reliably measuring fracture surface features.     

Biomass-derived materials for electrochemical energy storages

During the past decade humans have witnessed dramatic expansion of fundamental research as well as the commercialization in the area of electrochemical energy storage, which is driven by the urgent demand by portable electronic devices, electric vehicles, transportation and storage of renewable energy for the power grid in the clean energy economy. Li-secondary batteries and electrochemical capacitors can efficiently convert stored chemical energy into electrical energy, and are currently the rapid-growing rechargeable devices. However, the characteristic (including energy density, cost, and safety issues, etc.) reported for these current rechargeable devices still cannot meet the requirements for electric vehicles and grid energy storage, which are mainly caused by the limited properties of the key materials (e.g. anode, cathode, electrolyte, separator, and binder) employed by these devices. Moreover, these key materials are normally far from renewable and sustainable. Therefore great challenges and opportunities remain to be realized are to search green and low-cost materials with high performances. A large number of the properties of biomass materials-such as renewable, low-cost, earth-abundant, specific structures, mechanical property and many others-are very attractive. These properties endow that biomass could replace some key materials in electrochemical energy storage systems. In this review, we focus on the fundamentals and applications of biomass-derived materials in electrochemical energy storage techniques. Specifically, we summarize the recent advances of the utilization of various biomasses as separators, binders and electrode materials. Finally, several perspectives related to the biomass-derived materials for electrochemical energy storages are proposed based on the reported progress and our own evaluation, aiming to provide some possible research directions in this field.     

All-conjugated block copolymers

All-conjugated block copolymers of the rod-rod type came into the focus of interest because of their unique and attractive combination of nanostructure formation and electronic activity. Potential applications in a next generation of organic polymer materials for photovoltaic devices ("bulk heterojunction"-type solar cells) or (bio)sensors have been proposed. Combining the fascinating self-assembly properties of block copolymers with the active electronic and/or optical function of conjugated polymers in all-conjugated block copolymers is, therefore, a very challenging goal of synthetic polymer chemistry. First examples of such all-conjugated block copolymers from a couple of research groups all over the world demonstrate possible synthetic approaches and the rich application potential in electronic devices. A crucial point in such a development of novel polymer materials is a rational control over their nanostructure formation. All-conjugated di- or triblock copolymers may allow for an organization of the copolymer materials into large-area ordered arrays with a length scale of nanostructure formation of the order of the exciton diffusion length of organic semiconductors (typically ca. 10 nm). Especially for amphiphilic, all-conjugated copolymers the formation of well-defined supramolecular structures (vesicles) has been observed. However, intense further research is necessary toward tailor-made, all-conjugated block copolymers for specific applications. The search for optimized block copolymer materials should consider the electronic as well as the morphological (self-assembly) properties.     

Protein Needles as Molecular Templates for Artificial Metalloenzymes

Construction of artificial metalloenzymes based on protein assemblies is a promising strategy for the development of new catalysts, because the three-dimensional nanostructures of proteins with defined individual sizes can be used as molecular platforms that allow the arrangement of catalytic active centers on their surfaces. Protein needles/tubes/fibers are suitable for supporting various functional molecules, including metal complexes, synthetic molecules, metal nanoparticles, and enzymes with high densities and precise locations. Compared with bulk systems, the protein tube- and fiber-based materials have higher activities for catalytic reactions and electron transfer, as well as enhanced functions when used in electronic devices. The natural and synthetic protein tubes and fibers are constructed by self-assembly of monomer proteins or peptides. For more precise designs of arrangements of metal complexes, we have developed a new conceptual framework, based on the isolation of a robust needle structure from the cell-puncturing domains of a bacteriophage. The artificial protein needle shows great promise for use in creating efficient catalytic systems by providing the means to arrange the locations of various metal complexes on the protein surface. In this account, we discuss the recent development of protein needle-based metalloenzymes, and the future developments we are anticipating in this field.     

Recent advances in the approaches to recover rare earths and precious metals from E-waste: A mini-review

In the present day, with the rapid rate of advancements in technology, gadgets become obsolete very fast. The chase to keep up with the latest technologies diminishes the gadget's lifespan considerably. Consequently, they are discarded within a short time after their production, resulting in electronic waste (E-waste) being the fastest growing waste stream globally, with an annual production rate of 2.44 million short tonnes. The metals present in such E-waste provide several attractive properties, rendering them crucial in several applications as components of electronic and electrical devices. The major roadblock faced by mankind today is an effective technology with high recovery, low cost, and minimal environmental impact to recycle such electronic waste. In this mini-review, we elucidate the various recycling routes for metal extraction from waste and recent advances in the same. We have attempted to highlight the recent trends adopted by various researchers to recycle and extract valuable metals and rare earths from E-waste. Finally, the challenges and prospects in the extraction of rare earths and precious metals for E-waste research have been clearly brought out and suggestions have been made for future work.