Synthesis,Characterization, and Electroluminescent Properties of Iridium(III) 2-Phenylpyridine-type Complexes Containing Trifluoromethyl Substituents and Various Main-Group Moieties

New heteroleptic cyclometalated iridium(III) 2-phenylpyridine-type complexes with trifluoromethyl substituents and various main-group moieties were synthesized and their photophysical, electrochemical, and electroluminescent (EL) properties studied. The emission color can be tuned by a facile derivatization of the phenyl moiety of 2-phenylpyridine with various main-group moieties, and we have prepared new yellowish green to orange triplet emitters with enhanced charge injection/charge transporting features, which can furnish attractive EL performance in phosphorescent organic light-emitting devices (OLEDs). Attempts were also made to fabricate two-color white-light OLEDs based on a combination of fluorescent blue and phosphorescent orange emitters.     

Adhesive lithography for fabricating organic electronic and optoelectronics devices

Improvements in organic electronic materials have led to novel device applications, ranging from large-area flexible displays to lightweight plastic electronics. Progress on these applications would benefit from development of low-cost fabrication techniques for organic semiconductors. In this review, several fabrication processes based on adhesion force (i.e. van der Waals forces, thiol-metal reactions, and cold welding) are introduced. These patterning techniques are dry patterning techniques, i.e., the electronic materials are patterned from the raised regions of molds onto a substrate directly by additive or subtractive patterning methods. Patterning of organic small molecule, polymer thin films and metal electrodes by adhesive lithography is demonstrated. The operating properties of patterned organic light-emitting diodes (OLEDs) and organic thin film transistors (OTFTs) are comparable with the performance of devices fabricated by conventional evaporation deposition methods.     

Mechanism of Ir(ppy)3 Guest Exciton Formation with the Exciplex-Forming TCTA:TPBI Cohost within a Phosphorescent Organic Light-Emitting Diode Environment

Cohosts based on hole transporting and electron transporting materials often act as exciplexes in the form of intermolecular charge transfer complexes. Indeed, exciplex-forming cohosts have been widely developed as the host materials for efficient phosphorescent organic light-emitting diodes (OLEDs). In host–guest systems of OLEDs, the guest can be excited by two competing mechanisms, namely, excitation energy transfer (EET) and charge transfer (CT). Experimentally, it has been reported that the EET mechanism is dominant and the excitons are primarily formed in the host first and then transferred to the guest in phosphorescent OLEDs based on exciplex-forming cohosts. With this, exciplex-forming cohosts are widely employed for avoiding the formation of trapped charge carriers in the phosphorescent guest. However, theoretical studies are still lacking toward elucidating the relative importance between EET and CT processes in exciting the guest molecules in such systems. Here, we obtain the kinetics of guest excitation processes in a few trimer model systems consisting of an exciplex-forming cohost pair and a phosphorescent guest. We adopt the Förster resonance energy transfer (FRET) rate constants for the electronic transitions between excited states toward solving kinetic master equations. The input parameters for calculating the FRET rate constants are obtained from density functional theory (DFT) and time-dependent DFT. The results show that while the EET mechanism is important, the CT mechanism may still play a significant role in guest excitations. In fact, the relative importance of CT over EET depends strongly on the location of the guest molecule relative to the cohost pair. This is understandable as both the coupling for EET and the interaction energy for CT are strongly influenced by the geometric constraints. Understanding the energy transfer pathways from the exciplex state of cohost to the emissive state of guest may provide insights for improving exciplex-forming materials adopted in OLEDs.     

The modification of indium tin oxide with phosphonic acids: mechanism of binding, tuning of surface properties, and potential for use in organic electronic applications

Transparent metal oxides, in particular, indium tin oxide (ITO), are critical transparent contact materials for applications in next-generation organic electronics, including organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs). Understanding and controlling the surface properties of ITO allows for the molecular engineering of the ITO-organic interface, resulting in fine control of the interfacial chemistries and electronics. In particular, both surface energy matching and work function compatibility at material interfaces can result in marked improvement in OLED and OPV performance. Although there are numerous ways to change the surface properties of ITO, one of the more successful surface modifications is the use of monolayers based on organic molecules with widely variable end functional groups. Phosphonic acids (PAs) are known to bind strongly to metal oxides and form robust monolayers on many different metal oxide materials. They also demonstrate several advantages over other functionalizing moieties such as silanes or carboxylic acids. Most notably, PAs can be stored in ambient conditions without degradation, and the surface modification procedures are typically robust and easy to employ. This Account focuses on our research studying PA binding to ITO, the tunable properties of the resulting surfaces, and subsequent effects on the performance of organic electronic devices. We have used surface characterization techniques such as X-ray photoelectron spectroscopy (XPS) and infrared reflection adsorption spectroscopy (IRRAS) to determine that PAs bind to ITO in a predominantly bidentate fashion (where two of three oxygen atoms from the PA are involved in surface binding). Modification of the functional R-groups on PAs allows us to control and tune the surface energy and work function of the ITO surface. In one study using fluorinated benzyl PAs, we can keep the surface energy of ITO relatively low and constant but tune the surface work function. PA modification of ITO has resulted in materials that are more stable and more compatible with subsequently deposited organic materials, an effective work function that can be tuned by over 1 eV, and energy barriers to hole injection (OLED) or hole-harvesting (OPV) that can be well matched to the frontier orbital energies of the organic active layers, leading to better overall device properties.     

A New Class of Luminescent Platinum(II) Complexes of 1,3-Bis(N-alkylbenzimidazol-2′-yl)benzene-Type Ligands and Their Application Studies in the Fabrication of Solution-Processable Organic Light-Emitting Devices

A novel class of luminescent platinum(II) bzimb (1,3-bis(N-alkylbenzimidazol-2′-yl)benzene) complexes has been designed and synthesized. With the incorporation of various substituents on the anionic phenyl ring of the bzimb ligand, the emission color can be readily tuned. Their photophysical, electrochemical and electroluminescence properties have been studied. These platinum(II) bzimb complexes have been demonstrated to be capable of serving as phosphorescent dopants. Efficient solution-processable OLEDs (organic light-emitting devices), with a maximum external quantum efficiency of up to 4.85 %, can be achieved. This class of platinum(II) bzimb complexes represents a promising class of phosphorescent dopants for solution-processable OLEDs.     

反应喷墨打印技术及其在功能材料领域的研究进展

反应喷墨打印技术作为喷墨打印电子技术的重要分支,因其可以在沉积材料的同时可得到器件而受到人们的广泛关注.本文详细阐述了反应喷墨打印技术在功能材料制备领域,特别是在金属材料、高分子材料、无机材料等方面的研究进展,说明了反应喷墨打印用墨水是未来喷墨印刷电子研究的关键技术之一,简要介绍了反应喷墨打印技术与三维打印的联系,指出其在金属电路、有机发光二极管等印刷电子产业领域有广阔的应用前景.     

Metallo-organic Conjugated Systems for Organic Electronics

Polymer/organic optoelectronic devices have been the center of attention for the last two decades for both the academic and industrial research communities, due to their potential as a a low-cost, large-area, solution-processable technology alternative to their conventional, inorganic counterparts. There are several issues, such as the lower efficiencies, lower stabilities, and higher resistances of organic/polymer-based optoelectronic devices. To address these obstacles, significant research activity has been devoted to π-conjugated organics. One of the approaches includes the incorporation of metal complexes in the main conjugation or as a pendant substitution on that. Metallo-organic compounds with transition row elements have been extensively studied in organic electronics due to the easy tunability of their electronic properties, amenable redox matching, and the extended life-time of the triplet state. This has successfully resulted in some high performance electronic devices containing metallo-organic π-conjugated small molecules and polymers. Herein, we review the recent advances made in metallo-organic materials (small molecules and polymers) for organic electronics.     

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.     

$$\pi$$-Conjugated Heterocyclic fused Bithiophene Materials

This article covers the developments on the synthesis and properties of heterocyclic fused π-conjugated bithiophene materials that are potentially applicable in molecular electronics and optoelectronics. This fairly young strategy to efficiently tuning the electronic properties generates materials with very narrow band gaps. The nature of the central bridging heteroatom has a significant impact on the electronic and luminescence properties of these materials leading to intriguing species that can be employed in organic light emitting diodes (OLEDs) or organic field effect transistors (OFETs). So far a variety of heteroelements of group 13–16 (B, Si, Ge, Sn, N, P, S) have been investigated and incorporated into molecular as well as polymeric systems. A significant number of these materials can potentially act as organic emitters, electron or hole transport materials in organic devices but further studies are needed to optimize the necessary properties for the utility of this young class of compound in molecular electronics.     

Stretchable and self-healing polymers and devices for electronic skin

This review covers some of the most recent advances in stretchable and self-healing polymers and devices for Electronic skin (E-skin) applications. Applications for both stretchable and self-healing materials include, but are not limited to, electronics, displays, energy, the environment, and medicine. While the majority of organic materials can generally be rendered flexible, such materials are not stretchable, which is a key mechanical property necessary to realize applications of E-skin for prosthetics, artificial intelligence, systems for robotics, personal health monitoring, biocompatibility, and communication devices. In our effort to survey materials utilized in various components of an electronic device, we report herein recent advances in stretchable and self-healing conductors, semiconductors, and substrates. We highlight some key technologies recently developed in stretchable organic-based sensors, solar cells, light-emitting diodes, and self-healing electronic devices.     

Self-folding and aggregation of amyloid nanofibrils

Amyloids are highly organized protein filaments, rich in β-sheet secondary structures that self-assemble to form dense plaques in brain tissues affected by severe neurodegenerative disorders (e.g. Alzheimer's Disease). Identified as natural functional materials in bacteria, in addition to their remarkable mechanical properties, amyloids have also been proposed as a platform for novel biomaterials in nanotechnology applications including nanowires, liquid crystals, scaffolds and thin films. Despite recent progress in understanding amyloid structure and behavior, the latent self-assembly mechanism and the underlying adhesion forces that drive the aggregation process remain poorly understood. On the basis of previous full atomistic simulations, here we report a simple coarse-grain model to analyze the competition between adhesive forces and elastic deformation of amyloid fibrils. We use simple model system to investigate self-assembly mechanisms of fibrils, focused on the formation of self-folded nanorackets and nanorings, and thereby address a critical issue in linking the biochemical (Angstrom) to micrometre scales relevant for larger-scale states of functional amyloid materials. We investigate the effect of varying the interfibril adhesion energy on the structure and stability of self-folded nanorackets and nanorings and demonstrate that these aggregated amyloid fibrils are stable in such states even when the fibril-fibril interaction is relatively weak, given that the constituting amyloid fibril length exceeds a critical fibril length-scale of several hundred nanometres. We further present a simple approach to directly determine the interfibril adhesion strength from geometric measures. In addition to providing insight into the physics of aggregation of amyloid fibrils our model enables the analysis of large-scale amyloid plaques and presents a new method for the estimation and engineering of the adhesive forces responsible of the self-assembly process of amyloid nanostructures, filling a gap that previously existed between full atomistic simulations of primarily ultra-short fibrils and much larger micrometre-scale amyloid aggregates. Via direct simulation of large-scale amyloid aggregates consisting of hundreds of fibrils we demonstrate that the fibril length has a profound impact on their structure and mechanical properties, where the critical fibril length-scale derived from our analysis of self-folded nanorackets and nanorings defines the structure of amyloid aggregates. A multi-scale modeling approach as used here, bridging the scales from Angstroms to micrometres, opens a wide range of possible nanotechnology applications by presenting a holistic framework that balances mechanical properties of individual fibrils, hierarchical self-assembly, and the adhesive forces determining their stability to facilitate the design of de novo amyloid materials.     

An electrochromic device combining polypyrrole and WO3-I. Liquid electrolyte

In this work we assembled an electrochromic device using as active materials an organic conductive polymer and a transition metal oxide. We studied the materials used to assemble the device separately, and in complete devices. These materials were: polypyrrole doped with dodecylsulfate and tungsten oxide. The substrates used were glass slides coated with tin doped indium oxide, and the electrolyte was a propylene carbonate solution of lithium perchlorate. We adjusted the charge balance and the chromatic contrast of the devices by controlling the thickness of the polypyrrole films. To illustrate the results obtained, we describe two devices with different polypyrrole film thicknesses. The chromatic contrast in the visible and near-infrared wavelength range is 40% and the electrical and optical properties of the devices remain unchanged after 10⁴ double potential chronoamperometric steps.     

Phosphorescent chelating polyelectrolytes and their neutral precursors: Synthesis, characterizations, photoluminescence and electroluminescence

Novel chelating polyfluorene polyelectrolytes and their corresponding neutral precursors with Ir complex incorporated into polymer backbone were synthesized by Suzuki polycondensation reaction. The aminoalkyl or quaternized ammonium group provides good solubility of these phosphorescent polymers in alcohols which has a great advantage in fabrication of multi-layer polymer phosphorescent PLEDs. The photophysical and electroluminescent properties of the phosphorescent polyelectrolytes and their neutral precursors were investigated. The phosphorescent emission bands from both polyelectrolytes and neutral polymers which lie at around 640 nm displayed a saturated red emission. Devices fabricated from these phosphorescent polymers with air-stable high work function metals, such as Al, as cathode showed comparable device performance with low work function metals, such as Ba.     

Transfer-printed thin film metal electrodes for high-performance ferroelectric P(VDF-TrFE) devices

Electrodes formation method has been found to be very important in electronic devices using ferroelectric P(VDF-TrFE) copolymer. Depending on the deposition system used, vacuum-based deposition methods such as e-beam or thermal evaporation of metal electrodes has resulted in the performance deterioration, due to damages on the fragile organic surface by highly energetic particles such as intensive short-wavelength radiation, secondary electrons, etc. On the other hand, the transfer-printing of electrodes, which is formed on other substrates, onto the organic surface does not involve any such damages, leading to high-performance devices. Further, the transfer-printing process allows additional advantages of electrode surface tailoring or device fabrication on non-flat micro-rough surfaces. The proposed technique has led to much better performance of InGaZnO-based non-volatile memory transistors, compared to devices based on the direct evaporation of metal electrode. Transfer-printing of electrodes, instead of direct vacuum-based deposition, may lead to higher performing devices based on other organic electronic materials.     

Effect of triplet multiple quantum well structures on the performance of blue phosphorescent organic light-emitting diodes

We investigate multiple quantum well [MQW] structures with charge control layers [CCLs] to produce highly efficient blue phosphorescent organic light-emitting diodes [PHOLEDs]. Four types of devices from one to four quantum wells are fabricated following the number of CCLs which are mixed p- and n-type materials, maintaining the thickness of the emitting layer [EML]. Remarkably, such PHOLED with an optimized triplet MQW structure achieves maximum luminous and external quantum efficiency values of 19.95 cd/A and 10.05%, respectively. We attribute this improvement to the efficient triplet exciton confinement effect and the suppression of triplet-triplet annihilation which occurs within each EML. It also shows a reduction in the turn-on voltage from 3.5 V (reference device) to 2.5 V by the bipolar property of the CCLs.     

Aggregate nanostructures of organic molecular materials

Conjugated organic molecules are interesting materials because of their structures and their electronic, electrical, magnetic, optical, biological, and chemical properties. However, researchers continue to face great challenges in the construction of well-defined organic compounds that aggregate into larger molecular materials such as nanowires, tubes, rods, particles, walls, films, and other structural arrays. Such nanoscale materials could serve as direct device components. In this Account, we describe our recent progress in the construction of nanostructures formed through the aggregation of organic conjugated molecules and in the investigation of the optical, electrical, and electronic properties that depend on the size or morphology of these nanostructures. We have designed and synthesized functional conjugated organic molecules with structural features that favor assembly into aggregate nanostructures via weak intermolecular interactions. These large-area ordered molecular aggregate nanostructures are based on a variety of simpler structures such as fullerenes, perylenes, anthracenes, porphyrins, polydiacetylenes, and their derivatives. We have developed new methods to construct these larger structures including organic vapor-solid phase reaction, natural growth, association via self-polymerization and self-organization, and a combination of self-assembly and electrochemical growth. These methods are both facile and reliable, allowing us to produce ordered and aligned aggregate nanostructures, such as large-area arrays of nanowires, nanorods, and nanotubes. In addition, we can synthesize nanoscale materials with controlled properties. Large-area ordered aggregate nanostructures exhibit interesting electrical, optical, and optoelectronic properties. We also describe the preparation of large-area aggregate nanostructures of charge transfer (CT) complexes using an organic solid-phase reaction technique. By this process, we can finely control the morphologies and sizes of the organic nanostructures on wires, tubes, and rods. Through field emission studies, we demonstrate that the films made from arrays of CT complexes are a new kind of cathode materials, and we systematically investigate the effects of size and morphology on electrical properties. Low-dimension organic/inorganic hybrid nanostructures can be used to produce new classes of organic/inorganic solid materials with properties that are not observed in either the individual nanosize components or the larger bulk materials. We developed the combined self-assembly and templating technique to construct various nanostructured arrays of organic and inorganic semiconductors. The combination of hybrid aggregate nanostructures displays distinct optical and electrical properties compared with their individual components. Such hybrid structures show promise for applications in electronics, optics, photovoltaic cells, and biology. In this Account, we aim to provide an intuition for understanding the structure-function relationships in organic molecular materials. Such principles could lead to new design concepts for the development of new nonhazardous, high-performance molecular materials on aggregate nanostructures.     

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     

One-dimensional electrospun ceramic nanomaterials and their sensing applications

One-dimensional sensing materials that are prepared via electrospinning and controlled annealing exhibit intrinsic properties, such as electron transmissivity, magnetic susceptibility, specific heat capacity, as well as optical and mechanical characteristics. Particularly, the electronic transmission characteristics of the ceramic fiber materials, such as the electrical conductivity, photocurrent, magnetoresistance, nanocontact resistance, and dielectric properties, exhibited great potential for applications in the next generation of electronic sensing devices. First, electrospun ceramic materials with different structural and functional characteristics were reviewed here, after which the strategies for improving their properties, as well as the method for assembling the flexible devices, are summarized. Moreover, the electrospun ceramic nanofibers were detailedly discussed regarding applications in device construction and wearable electronics, such as photosensors, gas sensors, mechanical sensors, and other energy storage devices. Finally, the future development direction of the electrospinning technology for multifunctional and wearable electronics skin was proposed.     

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.     

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.