Xerox (Canada)

Conjugated polymers have been widely studied as potential semiconductor materials for organic thin-film transistors (TFTs). However, they have provided functionally poor transistor properties when the TFTs are fabricated in air. We have developed a class of liquid crystalline regioregular polythiophenes, PQTs, that possess sufficient air stability to enable achievement of excellent TFT properties under ambient conditions. These polythiophenes exhibit unique self-assembly ability and form highly structured thin films when deposited from solution under appropriate conditions. TFTs fabricated in air with PQT channel layers have provided high field-effect mobility to 0.14 cm2 V-1 s-1 and high current modulation to over 107, together with other desirable transistor properties. These high-performance polythiophenes will therefore help bring the long-standing concept of low-cost organic/polymer transistor circuits closer to commercial reality.

Studies on the long-term degradation of organic light-emitting devices (OLEDs) based on tris(8-hydroxyquinoline) aluminum (AlQ3), the most widely used electroluminescent molecule, reveal that injection of holes in AlQ3 is the main cause of device degradation. The transport of holes into AlQ3 caused a decrease in its fluorescence quantum efficiency, thus showing that cationic AlQ3 species are unstable and that their degradation products are fluorescence quenchers. These findings explain the success of different approaches to stabilizing OLEDs, such as doping of the hole transport layer, introducing a buffer layer at the hole-injecting contact, and using mixed emitting layers of hole and electron transporting molecules.

A microlens fabrication process is described which can be used in applications requiring integration of optical elements (lenses) and microcircuits. The process is fully compatible with 1C fabrication technology and uses commercially available 1C processing materials. The obtained microlenses are of excellent quality and basically show diffraction-limited resolution with ~1-microm spot size. Extensions of the process to production of nonspherical lenses and use of alternative material packages are also discussed.

A facile synthesis of stable silver nanoparticles having a particle size of <10 nm is described. The synthesis involved reduction of silver acetate with a substituted hydrazine, such as PhNHNH2, in the presence of a 1-alkylamine, such as C16H33NH2, in toluene at 25-60 degrees C. Spin-coated thin films or printed electronic features of alkylamine-stabilized silver nanoparticles could be easily converted at 120-160 degrees C into highly conductive films or elements with conductivity of 2-4 x 104 S cm-1. Organic thin-film transistors with printed silver source/drain electrodes of this nature exhibited field-effect transistor properties which are similar to those of the devices using vacuum-deposited silver electrodes.

A stable, high-mobility ZnO thin-film semiconductor was fabricated by thermal treatment of a solution-deposited thin film from a solution of Zn(OAc) 2 /2-ethanolamine in methoxyethanol. This ZnO thin-film semiconductor was composed of closely packed ZnO single crystals (∼30 to 50 nm) having a hexagonal structure assuming a preferred orientation with its c -axis perpendicular to the substrate. Field-effect mobility of 5−6 cm 2 V -1 s -1 and current on-to-off ratio of 10 5 −10 6 were demonstrated with this ZnO thin-film semiconductor in thin-film transistors.

ADVERTISEMENT RETURN TO ISSUEPREVNoteNEXTLigand-Accelerated Catalysis of the Ullmann Condensation: Application to Hole Conducting TriarylaminesH. Bruce Goodbrand and Nan-Xing HuView Author Information Xerox Research Centre of Canada, 2660 Speakman Drive, Mississauga, Ontario, Canada L5K 2L1 Cite this: J. Org. Chem. 1999, 64, 2, 670–674Publication Date (Web):December 31, 1998Publication History Received4 September 1998Published online31 December 1998Published inissue 1 January 1999https://pubs.acs.org/doi/10.1021/jo981804ohttps://doi.org/10.1021/jo981804obrief-reportACS PublicationsCopyright © 1999 American Chemical SocietyRequest reuse permissionsArticle Views7035Altmetric-Citations373LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Anions,Catalysis,Catalysts,Condensation,Ligands Get e-Alerts

Three 8-hydroxyquinolato (q) boron compounds B(C 2 H 5 ) 2 q ( 1 ), BPh 2 q ( 2 ), and B(2-naph) 2 q ( 3 ) have been synthesized by the reaction of 8-hydroxyquinoline with an appropriate BR 3 compound. Compounds 1 − 3 have a tetrahedral geometry as demonstrated by the structure of 1 determined by a single-crystal X-ray diffraction analysis. Compounds 1 − 3 emit a green-blue color at λ max = 495−500 nm when irradiated by UV light. The electroluminescent (EL) properties of 2 and 3 were examined by fabricating EL devices using 2 and 3 as the light-emitting layer, respectively. The devices of 2 produce a yellow-green light with broad emission spectra, attributed to the formation of an exciplex of 2 with the N, N ‘ -di-1-naphthyl- N, N ‘ -diphenylbenzidine (NPB) in the hole transport layer while the intrinsic EL emission of compound 3 was observed. Both 2 and 3 were found to be good electron transport materials in EL devices.

Poly(4,8-dialkyl-2,6-bis(3-alkylthiophen-2-yl)benzo[1,2- b:4,5- b ‘]dithiophene) 1 represents a new class of polymer semiconductors which self-assemble into higher structural orders without thermal annealing and provide excellent field-effect transistor performance with mobility up to 0.25 cm 2 V -1 s -1 when used as a solution-processed thin-film semiconductor in thin-film transistors.

Abstract Herein a novel synthetic route is described for the production of thermally stable, structurally well‐defined two‐dimensional (2D) hexagonal mesoporous nanocrystalline anatase (meso‐nc‐TiO 2 ), with a large pore diameter, narrow pore‐size distribution, high surface area, and robust inorganic walls comprised of nanocrystalline anatase. The synthetic approach involves the evaporation‐induced co‐assembly of a non‐ionic amphiphilic triblock‐copolymer template and titanium tetraethoxide, but with a pivotal change in the main solvent of the system, where the commonly used ethanol is replaced with 1‐butanol. This seemingly minor modification in solvent type from ethanol to 1‐butanol turns out to be the key synthetic strategy for achieving a robust, structurally well‐ordered meso‐nc‐TiO 2 material in the form of either thick or thin films. The beneficial “solvent” effect originates from the higher hydrophobicity of 1‐butanol than ethanol, enhancing microphase separation and templating, lower critical micelle concentration of the template in 1‐butanol, and the ability to increase the relative concentration of the inorganic precursor to template in the co‐assembly synthesis. Moreover, thin films with dimensions of several centimeters that are devoid of cracks down to the length scale of the mesostructure itself, having high porosity, well‐defined mesostructural features, and semi‐crystalline pore walls were straightforwardly and reproducibly obtained as a result of the physicochemical property advantages of 1‐butanol over ethanol within our synthesis scheme.

The time-dependent Smoluchowski equation with a Coulomb potential is solved analytically for a general boundary condition, and expressions for the distribution function, reaction rate, and survival probability are given. The expressions are evaluated numerically and the long-time behavior is derived. The theoretical results apply to experiments involving ion recombination without an electric field (or where there is a time delay in the application of the field), to scavenging experiments, and to fluorescence quenching.

Proper functionalization of indolo[3,2-b]carbazole led to a new class of high-performance organic semiconductors suitable for organic thin-film transistor (OTFT) applications. While 5,11-diaryl-substituted indolo[3,2-b]carbazoles without long alkyl side chains provided amorphous thin films upon vacuum deposition, those with sufficiently long alkyl side chains such as 5,11-bis(4-octylphenyl)indolo[3,2-b]carbazole self-organized readily into highly crystalline layered structures under similar conditions. OTFTs using channel semiconductors of this nature exhibited excellent field-effect properties, with mobility up to 0.12 cm(2) V(-1) s(-1) and current on/off ratio to 10(7). As this class of organic semiconductors has relatively low HOMO levels and large band gaps, they also displayed good environmental stability even with prolonged exposure to amber light, an appealing characteristic for OTFT applications.

A generalized model of multiple trapping from a band of extended or localized states is used to study timedependent charge transport in amorphous solids. The model differs from a conventional multiple-trapping model by including a distribution of trap release rates for a constant trap energy. An extensive analysis of transient photocurrent experiments on $a\ensuremath{-}\mathrm{S}\mathrm{e}$ is carried out to determine the transport parameters for this case. It is found that a small number of parameters can be used to analyze the experimental results over a wide range of temperature and sample thickness. The results of the analysis are interpreted in terms of trapcontrolled hopping, which is a special case of the generalized multiple-trapping model. The asymptotic value of the theoretical photocurrent transient is obtained for the multiple-trapping model, and the results of Scher and Montroll are recovered for the case of extreme or anomalous dispersion, which occurs for $a\ensuremath{-}\mathrm{S}\mathrm{e}$ at low temperature ($T\ensuremath{\simeq}140$ K). The density of trapping sites is estimated, and the difficulties associated with considering a continuous distribution of trap release rates are discussed. It is concluded that the generalized multiple-trapping model, defined by simple first-order rate equations, is capable of describing detailed shapes of photocurrent transients, including dispersive and nondispersive charge transport.

Structurally ordered organic semiconductor nanoparticles, which form a stable nanoparticle dispersion in an appropriate liquid, are generated from regioregular poly(3,3‴-didodecylquarterthiophene) (PQT-12). This dispersion enables facile solution fabrication of high-performance semiconductor layers composed of extensive crystalline domains of lamellar π–π stacks (see Figure), yielding organic thin-film transistors with excellent field-effect-transistor properties.

Studies of electroluminescence degradation mechanisms in small-molecule-based organic light-emitting devices (OLEDs) are reviewed. Luminescence degradation due to the growth of visible nonemissive defects, widely referred to as "dark spots", as well as device catastrophic failure phenomena are addressed briefly. A special emphasis is given to intrinsic degradation phenomena that cause the decrease in the electroluminescence efficiency of the OLEDs during operation. In the discussion of intrinsic degradation, some widely accepted models that have been proposed to explain the degradation behavior are introduced and reviewed in view of experimental observations. These models are (i) the morphological instability model, (ii) the unstable cationic AlQ3 model, (iii) the indium migration model, (iv) the mobile ionic impurities model, and (v) the immobile positive charge accumulation model.

Given the emergence of data science and machine learning throughout all aspects of society, but particularly in the scientific domain, there is increased importance placed on obtaining data. Data in materials science are particularly heterogeneous, based on the significant range in materials classes that are explored and the variety of materials properties that are of interest. This leads to data that range many orders of magnitude, and these data may manifest as numerical text or image-based information, which requires quantitative interpretation. The ability to automatically consume and codify the scientific literature across domains—enabled by techniques adapted from the field of natural language processing—therefore has immense potential to unlock and generate the rich datasets necessary for data science and machine learning. This review focuses on the progress and practices of natural language processing and text mining of materials science literature and highlights opportunities for extracting additional information beyond text contained in figures and tables in articles. We discuss and provide examples for several reasons for the pursuit of natural language processing for materials, including data compilation, hypothesis development, and understanding the trends within and across fields. Current and emerging natural language processing methods along with their applications to materials science are detailed. We, then, discuss natural language processing and data challenges within the materials science domain where future directions may prove valuable.

Printed organic thin-film transistors (OTFTs) have received great interests as potentially low-cost alternative to silicon technology for application in large-area, flexible, and ultra-low-cost electronics. One of the critical materials for TFTs is semiconductor, which has a dominant impact on the transistor properties. We review here the structural studies and design of thiophene-based polymer semiconductors with respect to solution processability, ambient stability, molecular self-organization, and field-effect transistor properties for OTFT applications. We show that through judicial monomer design, delicately controlled pi-conjugation, and strategically positioned pendant side-chain distribution, novel solution-processable thiophene polymer semiconductors with excellent self-organization ability to form extended lamellar pi-stacking orders can be developed. OTFTs using semiconductors of this nature processed in ambient conditions have provided excellent field-effect transistor properties.

Herein we report a novel self-assembly synthesis, structural and optical characterization of mesoporous Bragg stacks (MBS) composed of spin-coated multilayer stacks of mesoporous TiO(2) and mesoporous SiO(2). Investigation of the optical response of MBS to the infiltration of alcohols and alkanes into its pores reveals better sensitivity and selectivity than conventional Bragg reflectors. Furthermore, we demonstrate that the chemical sensing ability can be tuned via layer thickness, composition and surface properties.

Thin-film transistor (TFT) backplanes fabricated by using jet printing as the only patterning method are reported. Additive and subtractive printing processes are combined to make 128×128 pixel active matrix arrays with 340μm pixel size. The semiconductor used, a regioregular polythiophene, poly[5,5′-bis(3-dodecyl-2-thienyl)-2,2′-bithiophene]; (PQT-12) is deposited by inkjet printing and exhibits average TFT mobility of 0.06cm2∕Vs, on/off ratios of 106, and minimal bias stress. The printed TFTs have high yield with a narrow performance distribution. The pixel design benefits from the registration accuracy of jet printing and it is shown that the electrical performance is suitable for addressing capacitive media displays.

The transport properties of high-performance thin-film transistors (TFT) made with a regioregularpoly(thiophene) semiconductor (PQT-12) are reported. The room-temperature field-effect mobility of the devices varied between 0.004 and $0.1\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$ and was controlled through thermal processing of the material, which modified the structural order. The transport properties of TFTs were studied as a function of temperature. The field-effect mobility is thermally activated in all films at $T&lt;200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and the activation energy depends on the charge density in the channel. The experimental data are compared to theoretical models for transport, and we argue that a model based on the existence of a mobility edge and an exponential distribution of traps provides the best interpretation of the data. The differences in room-temperature mobility are attributed to different widths of the shallow localized state distribution at the edge of the valence band due to structural disorder in the film. The free carrier mobility of the mobile states in the ordered regions of the film is the same in all structural modifications and is estimated to be between 1 and $4\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$.

We report electroluminescence degradation studies of tris (8-hydroxyquinoline) aluminum (Alq3) organic light-emitting devices (OLEDs) under ambient conditions. Alq3 films and organic bilayer anode/naphthyl-substituted benzidine derivative/Alq3/cathode devices are studied via electroluminescence, photoluminescence, polarization microscopy and atomic force microscopy, and via microscopic infrared spectroscopy. Results reveal that humidity induces the formation of crystalline Alq3 structures in originally amorphous films. The same phenomenon is found to occur in OLEDs and causes cathode delamination at the Alq3/cathode interface that results in the formation of black (nonemissive) spots in the devices.