Enhanced Charge Carrier Mobility Research Articles

(Invited) Less Is More: Thermoelectric Performance Enhancements in Polymer-Free Semiconducting Single-Walled Carbon Nanotube Networks

There is a growing interest in the use of carbon nanostructures for a variety of electronic and optoelectronic technologies, including energy harvesting applications such as photovoltaics (PV) and thermoelectrics (TE). We will present a series of studies aimed at improving the TE performance of semiconducting single-walled carbon nanotube (s-SWCNT) thin film networks. The optical and electrical performance of SWCNT ensembles is often limited by the presence of metallic single-walled carbon nanotube (m-SWCNT). We will demonstrate a polymer-based purification strategy that effectively eliminates these, and other impurities, from the raw material, leaving s-SWCNTs in extremely high purity. Modification of this extraction process produces s-SWCNT thin film networks where the polymer can be completely removed, resulting in close tube-tube contacts in a dense s-SWCNT network. Removal of the polymer in the solid state, rather than in solution, also minimizes nanotube bundling during network formation. By controlling the bundle size and extent of polymer remaining in the s-SWCNT network we demonstrate TE power factors that almost double the performance of s-SWCNT networks previously demonstrated. We trace the improved performance to an enhanced electrical conductivity, resulting from improved doping and strongly enhanced charge carrier mobility, and analyze our data within the framework of a recently developed thermoelectric transport model. Finally, we demonstrate that the removal of the polymer from the s-SWCNT network has negligible impact on the thermal conductivity, which appears to be limited by dopant-induced phonon scattering processes. These observations demonstrate the ability to exert exquisite control of the thermoelectric performance by controlling the composition of the s-SWCNT network and tuning the carrier density (i.e., Fermi energy), and touts SWCNTs as an avenue for realizing thermally stable room temperature thermoelectric devices fashioned from inexpensive and abundant organic constituents.

Separation of Semiconducting Carbon Nanotubes for Flexible and Stretchable Electronics Using Polymer Removable Method.

Electronics that are soft, conformal, and stretchable are highly desirable for wearable electronics, prosthetics, and robotics. Among the various available electronic materials, single walled carbon nanotubes (SWNTs) and their network have exhibited high mechanical flexibility and stretchability, along with comparable electrical performance to traditional rigid materials, e.g. polysilicon and metal oxides. Unfortunately, SWNTs produced en masse contain a mixture of semiconducting (s-) and metallic (m-) SWNTs, rendering them unsuitable for electronic applications. Moreover, the poor solubility of SWNTs requires the introduction of insulating surfactants to properly disperse them into individual tubes for device fabrication. Compared to other SWNT dispersion and separation methods, e.g., DNA wrapping, density gradient ultracentrifugation, and gel chromatography, polymer wrapping can selectively disperse s-SWNTs with high selectivity (>99.7%), high concentration (>0.1 mg/mL), and high yield (>20%). In addition, this method only requires simple sonication and centrifuge equipment with short processing time down to 1 h. Despite these advantages, the polymer wrapping method still faces two major issues: (i) The purified s-SWNTs usually retain a substantial amount of polymers on their surface even after thorough rinsing. The low conductivity of the residual polymers impedes the charge transport in SWNT networks. (ii) Conjugated polymers used for SWNT wrapping are expensive. Their prices ($100-1000/g) are comparable or even higher than those of SWNTs ($10-300/g). These utilized conjugated polymers represent a large portion of the overall separation cost. In this Account, we summarize recent progresses in polymer design for selective dispersion and separation of SWNTs. We focus particularly on removable and/or recyclable polymers that enable low-cost and scalable separation methods. First, different separation methods are compared to show the advantages of the polymer wrapping methods. In specific, we compare different characterization methods used for purity evaluation. For s-SWNTs with high purity, i.e., >99%, short-channel (smaller than SWNT length) electrical measurement is more reliable than optical methods. Second, possible sorting mechanism and molecular design strategies are discussed. Polymer parameters such as backbone design and side chain engineering affect the polymer-SWNT interactions, leading to different dispersion concentration and selectivity. To address the above-mentioned limiting factors in both polymer contamination and cost issues, we describe two important polymer removal and cycling approaches: (i) changing polymer wrapping conformation to release SWNTs; (ii) depolymerization of conjugated polymer into small molecular units that have less affinity toward SWNTs. These methods allow the removal and recycling of the wrapping polymers, thus providing low-cost and clean s-SWNTs. Third, we discuss various applications of polymer-sorted s-SWNTs, including flexible/stretchable thin-film transistors, thermoelectric devices, and solar cells. In these applications, polymer-sorted s-SWNTs and their networks have exhibited good processability, attractive mechanical properties, and high electrical performance. An increasing number of studies have shown that the removable polymer approaches can completely remove polymer residues in SWNT networks and lead to enhanced charge carrier mobility, higher conductivity, and better heterojunction interface.

Enhanced Charge Carrier Mobility and Tailored Luminescence of n‐Type Organic Semiconductor through Block Copolymer Supramolecular Assembly

Herein, a novel and viable strategy to fabricate fully solution processable nanostructured n‐type organic semiconducting material through block copolymer supramolecular assembly consisting of polystyrene‐b‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) and an asymmetric perylenebisimide (PBI) has been demonstrated. The block copolymer supramolecular assemblies show hierarchical structure formation in two length scales (lamella within lamella) from synergistic phase separation of block copolymer and PBI molecule inside the comb block. The optical and luminescent studies clearly evidence that the nature of aggregation of the PBI molecules inside the P4VP domain through facial π–π stacking is modified with tailored luminescent properties compared to its pure state. The block copolymer supramolecular assembly with 1:1 mole ratio (4‐vinyl pyridine:PBI) shows almost three‐order enhancement of charge carrier mobility compared to pristine PBI though it has only (0.571) of PBI weight fraction. It is believed that the organic semiconductor polymeric system described here will be useful for preparing luminescent materials, organic electronic and optoelectronic devices. image

Epitaxial Growth of Large-Grain NiSe Films by Solid-State Reaction for High-Responsivity Photodetector Arrays.

Film-based photodetectors have shown superiority for the fabrication of photodetector arrays, which are desired for integrating photodetectors into sensing and imaging systems, such as image sensors. But they usually possess a low responsivity due to low carrier mobility of the film consisting of nanocrystals. Large-grain semiconductor films are expected to fabricate superior-responsivity photodetector arrays. However, the growth of large-grain semiconductor films, normally with a nonlayer structure, is still challenging. Herein, this study introduces a solid-state reaction method, in which the growth rate is supposed to be limited by diffusion and reaction rate, for interface-confined epitaxial growth of nonlayer structured NiSe films with grain size up to micrometer scale on Ni foil. Meanwhile, patterned growth of NiSe films allows the fabrication of NiSe film based photodetector arrays. More importantly, the fabricated photodetector based on as-grown high-quality NiSe films shows a responsivity of 150 A W-1 in contrast to the value of 0.009 A W-1 from the photodetector based on as-deposited NiSe film consisting of nanocrystals, indicating a huge responsivity-enhancement up to four orders of magnitude. It is ascribed to the enhanced charge carrier mobility in as-grown NiSe films by dramatically decreasing the amount of grain boundary leading to scattering of charge carrier.

Functionalization of TiO2 Nanofibers with Ag and Ag2S Nanoparticles for Enhanced Photocatalytic Hydrogen Generation

One-dimensional (1D) nanomaterials owing to their unique properties, including semi-directed charge transport, enhanced charge carrier mobility and more active sites, make them intriguing materials for application in photocatalysis. In this work, a simple electrospinning method was used to synthesize 1D TiO2 and TiO2/Ag nanofibers, followed by calcination in air at 500 °C for 2 h to achieve anatase crystalline nanofibers. TiO2/Ag2S composite nanofibers was prepared through hydrothermal treatment of TiO2/Ag nanofibers using Thiourea as the sulfur source for sulfidation. The photocatalytic activities of the as-prepared nanofibers were tested for hydrogen evolution from water with methanol as the sacrificial reagent under the simulated solar irradiation. The results indicate that by incorporating Ag nanoparticles into 1D TiO2 nanofibers largely enhanced the photocatalytic hydrogen evolution with the best Ag nanoparticles loading amount of ~10 at.%. Furthermore, it was found that the efficiency of photocatalytic hydrogen evolution was further improved after sulfidation of TiO2/Ag nanofibers, which indicates that TiO2/Ag2S nanofibers are efficient photocatalyst. Compared with pure TiO2 and TiO2/Ag nanofibers, the TiO2/Ag2S composite nanofibers have the highest photocatalytic activities, and the optimal sulfidation condition was achieved with 150 mg of Thiourea in hydrothermal treatment. The Ag2S nanoparticles have a dual function as improving charge separation and broaden the light absorption spectrum of the photocatalyst. This synthetic methodology described in this work is a promising approach to fabricate nanostructures with high throughput under mild condition for enhanced photocatalytic applications.

Supramolecular control over the morphology of bio-inspired poly(3-hexylthiophene) for organic thin film transistors

We have developed a strategy for modifying the channel layer of organic thin film transistors (OTFTs) through side-chain induced self-organization into a well-ordered film. To obtain selectively self-patterned layers, we treated an adenine-functionalized poly(3-hexylthiophene) (PAT) with adenosine triphosphate (ATP). Using this strategy, interchain charge transport resulting from π-conjugation was selected to control the polymer morphology, without the need of additional chemical synthetic processing. The side chain–induced self-organization can be understood in terms of supramolecular interactions. The π-electrons were delocalized among the thiophene rings, thereby improving the interchain charge transport ability; the resulting planar π-electron system in PAT:ATP resulted in closer intermolecular π–π distances, facilitating enhanced charge carrier mobility within a fibrillar structure. The PAT:ATP-based OTFT device exhibited moderate to improved electronic characteristics, with an average field mobility of 3.2 × 10−4 cm2 V−1 s−1 at −30 V and a threshold voltage (Vth) of 5 V, and an on/off current ratio of 106. This method has great potential for inducing selective intermolecular interactions in fully solution processed electronic devices.

Novel Effects of Compressed CO2 Molecules on Structural Ordering and Charge Transport in Conjugated Poly(3-hexylthiophene) Thin Films.

We report the effects of compressed CO2 molecules as a novel plasticization agent for poly(3-hexylthiophene) (P3HT)-conjugated polymer thin films. In situ neutron reflectivity experiments demonstrated the excess sorption of CO2 molecules in the P3HT thin films (about 40 nm in thickness) at low pressure (P = 8.2 MPa) under the isothermal condition of T = 36 °C, which is far below the polymer bulk melting point. The results proved that these CO2 molecules accelerated the crystallization process of the polymer on the basis of ex situ grazing incidence X-ray diffraction measurements after drying the films via rapid depressurization to atmospheric pressure: both the out-of-plane lamellar ordering of the backbone chains and the intraplane π-π stacking of the side chains were significantly improved, when compared with those in the control P3HT films subjected to conventional thermal annealing (at T = 170 °C). Electrical measurements elucidated that the CO2-annealed P3HT thin films exhibited enhanced charge carrier mobility along with decreased background charge carrier concentration and trap density compared with those in the thermally annealed counterpart. This is attributed to the CO2-induced increase in polymer chain mobility that can drive the detrapping of molecular oxygen and healing of conformational defects in the polymer thin film. Given the universality of the excess sorption of CO2 regardless of the type of polymers, the present findings suggest that CO2 annealing near the critical point can be useful as a robust processing strategy for improving the structural and electrical characteristics of other semiconducting conjugated polymers and related systems such as polymer:fullerene bulk heterojunction films.

Remarkable enhancement of charge carrier mobility of conjugated polymer field-effect transistors upon incorporating an ionic additive.

Organic semiconductors with high charge carrier mobilities are crucial for flexible electronic applications. Apart from designing new conjugated frameworks, different strategies have been explored to increase charge carrier mobilities. We report a new and simple approach to enhancing the charge carrier mobility of DPP-thieno[3,2-b]thiophene-conjugated polymer by incorporating an ionic additive, tetramethylammonium iodide, without extra treatments into the polymer. The resulting thin films exhibit a very high hole mobility, which is higher by a factor of 24 than that of thin films without the ionic additive under the same conditions. On the basis of spectroscopic grazing incidence wide-angle x-ray scattering and atomic force microscopy studies as well as theoretical calculations, the remarkable enhancement of charge mobility upon addition of tetramethylammonium iodide is attributed primarily to an inhibition of the torsion of the alkyl side chains by the presence of the ionic species, facilitating a more ordered lamellar packing of the alkyl side chains and interchain π-π interactions.

Hybrid quantum dot-tin disulfide field-effect transistors with improved photocurrent and spectral responsivity

We report an improved photosensitivity in few-layer tin disulfide (SnS2) field-effect transistors (FETs) following doping with CdSe/ZnS core/shell quantum dots (QDs). The hybrid QD-SnS2 FET devices achieve more than 500% increase in the photocurrent response compared with the starting SnS2-only FET device and a spectral responsivity reaching over 650 A/W at 400 nm wavelength. The negligible electrical conductance in a control QD-only FET device suggests that the energy transfer between QDs and SnS2 is the main mechanism responsible for the sensitization effect, which is consistent with the strong spectral overlap between QD photoluminescence and SnS2 optical absorption as well as the large nominal donor-acceptor interspacing between QD core and SnS2. We also find enhanced charge carrier mobility in hybrid QD-SnS2 FETs which we attribute to a reduced contact Schottky barrier width due to an elevated background charge carrier density.

X-ray imaging with scintillator-sensitized hybrid organic photodetectors

Medical X-ray imaging requires cost-effective and high-resolution flat-panel detectors for the energy range between 20 and 120 keV. Solution-processed photodetectors provide the opportunity to fabricate detectors with a large active area at low cost. Here, we present a disruptive approach that improves the resolution of such detectors by incorporating terbium-doped gadolinium oxysulfide scintillator particles into an organic photodetector matrix. The X-ray induced light emission from the scintillators is absorbed within hundreds of nanometres, which is negligible compared with the pixel size. Hence, optical crosstalk, a limiting factor in the resolution of scintillator-based X-ray detectors, is minimized. The concept is validated with a 256 × 256 pixel detector with a resolution of 4.75 lp mm−1 at a MTF = 0.2, significantly better than previous stacked scintillator-based flat-panel detectors. We achieved a resolution that proves the feasibility of solution-based detectors in medical applications. Time-resolved electrical characterization showed enhanced charge carrier mobility with increased scintillator filling, which is explained by morphological changes.

Formulation Of SnO2/graphene Nanocomposite Modified Electrode For Synergitic Electrochemcial Detection Of Dopamine

Pristine SnO2 and SnO2/Graphene (SnO2/GN) nanocomposites were prepared via facile hydrothermal method with amended electro catalytic activity towards Dopamine (DA) sensing. X-Ray Diffraction (XRD) pattern revealed the formation of tetragonal crystal system of SnO2 that was retained in both pure metal oxide and composite. Fourier Transform – Infrared (FT-IR) transmission spectra evidenced the stretching and bending vibration modes of pure SnO2 and SnO2/GN nanocomposites. The in-plane bending modes of SnO2 and graphatic peaks in graphene oxide (GO) and composite were identified in Raman spectral analysis. Morphology of synthesized materials and uniform distribution of SnO2 on graphene sheet in SnO2/GN composite were observed in Field Emission-Scanning Electron Microscope (FE-SEM). Electrochemical performance of SnO2 and SnO2/GN nanocomposite on modified Glassy Carbon (GC) electrode was evaluated for direct DA sensing using Cyclic Voltammetry (CV), Differential Pulse Voltammetry (DPV) and Chrono Amperometric techniques. The SnO2/GN nanocomposite showed enhanced charge carrier mobility towards DA in presence of interferences like Ascorbic acid (AA) and Uric acid (UA) compared to pristine SnO2. The limit of detection was calculated as (0.7μM) for (SnO2/GN) which is better than bare SnO2 (6.675 μM). These synergetic behaviors depicting SnO2/GN composite can serve as a promising electrode in sensor transducers in near future.

Role of the dopant aluminum for the growth of sputtered ZnO:Al investigated by means of a seed layer concept

This work elucidates the effect of the dopant aluminum on the growth of magnetron-sputtered aluminum-doped zinc oxide (ZnO:Al) films by means of a seed layer concept. Thin (<100 nm), highly doped seed layers and subsequently grown thick (∼800 nm), lowly doped bulk films were deposited using a ZnO:Al2O3 target with 2 wt. % and 1 wt. % Al2O3, respectively. We investigated the effect of bulk and seed layer deposition temperature as well as seed layer thickness on electrical, optical, and structural properties of ZnO:Al films. A reduction of deposition temperature by 100 °C was achieved without deteriorating conductivity, transparency, and etching morphology which renders these low-temperature films applicable as light-scattering front contact for thin-film silicon solar cells. Lowly doped bulk layers on highly doped seed layers showed smaller grains and lower surface roughness than their counterpart without seed layer. We attributed this observation to the beneficial role of the dopant aluminum that induces an enhanced surface diffusion length via a surfactant effect. The enhanced surface diffusion length promotes 2D-growth of the highly doped seed layer, which is then adopted by the subsequently grown and lowly doped bulk layer. Furthermore, we explained the seed layer induced increase of tensile stress on the basis of the grain boundary relaxation model. The model relates the grain size reduction to the tensile stress increase within the ZnO:Al films. Finally, temperature-dependent conductivity measurements, optical fits, and etching characteristics revealed that seed layers reduced grain boundary scattering. Thus, seed layers induced optimized grain boundary morphology with the result of a higher charge carrier mobility and more suitable etching characteristics. It is particularly compelling that we observed smaller grains to correlate with an enhanced charge carrier mobility. A seed layer thickness of 5 nm was sufficient to induce the beneficial effects.

Cationic Water-Soluble Conjugated Polyelectrolytes/Graphene Oxide Nanocomposites as Efficient Green Hole Injection Layers in Organic Light Emitting Diodes

The current research presents using a nanocomposite comprising of a cationic conjugated polyelectrolyte (CPE), poly[(2,5-bis(2-(N,N-diethylammonium bromide)ethoxy)-1,4-phenylene)-alt-1,4-phenylene] or (PPPNEt2·HBr), with graphene oxide (GO) as a new hole injection layer (HIL) for organic light emitting diodes. It is demonstrated that using the designed ionically functionalized water-soluble conjugated polymers instead of polyethylene dioxythiophene:polystyrenesulfonate (PEDOT:PSS) is a promising approach to overcome the strong acidic nature of PEDOT:PSS besides excluding its nonconductive PSS part. As the other aspiration of this work, we introduce a good partner for dissolving and spin-casting of GO as a simple and economic technique to use the hole conductive and electron blocking nature of GO in the hole injection portion of assembled devices. Using this new binary blend showed enhanced charge carrier mobility, good electroluminescence, and J–V characteristics in comparison with conventional devices. Such improvement is interpreted with induced ion space charge of HIL at the interface and resulting electric field screening effect due to ion migration.

Rational Design of Small Molecular Donor for Solution‐Processed Organic Photovoltaics with 8.1% Efficiency and High Fill Factor via Multiple Fluorine Substituents and Thiophene Bridge

A series of tetrafluorine‐substituted small molecules with a D1‐A‐D2‐A‐D1 linear framework based on indacenodithiophene and difluorobenzothiadiazole is designed and synthesized for application as donor materials in solution‐processed small‐molecule organic solar cells. The impacts of thiophene π‐bridge and multiple fluorinated modules on the photophysical properties, the energy levels of the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO), charge carrier mobility, the morphologies of blend films, and their photovoltaic properties as electron donor material in the photoactive layer are investigated. By incorporating multiple fluorine substituents of benzothiadiazole and inserting two thiophene spacers, the fill factor (FF), open‐circuit voltage, and short‐circuit current density are dramatically improved in comparison with fluorinated‐free materials. With the solvent vapor annealing treatment, further enhancement in charge carrier mobility and power conversion efficiency (PCE) are achieved. Finally, a high PCE of 8.1% with very‐high FF of 0.76 for BIT‐4F‐T/PC71BM is achieved without additional additive, which is among one of the highest reported for small‐molecules‐based solar cells with PCE over 8%. The results reported here clearly indicate that high PCE in solar cells based small molecules can be significantly increased through careful engineering of the molecular structure and optimization on the morphology of blend films by solvent vapor annealing.

Enhanced thermoelectric performance of highly conductive poly(3,4-ethylenedioxythiophene)/carbon black nanocomposites for energy harvesting

The thermoelectric performance of para-methylbenzenesulfonate (p-MeBzs) doped highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) can be improved by the use of carbon black fillers. Thermoelectric nanocomposites were prepared via chemical polymerization. Dodecylbenzenesulfonic acid (DBSA) was introduced before polymerization to act simultaneously as a surfactant for formation of micelles of carbon black and as a doping agent. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) were employed to characterize the morphology of PEDOT coated carbon black and PEDOT. Electrical conductivity of the composites improved with increase in weight percentage of carbon black from 0% to 30%. Extended chain conformations and increase in electron delocalization reduces the carrier hopping barriers. These contribute to the enhancement of charge carrier mobility. Although electrical conductivity is directly proportional to the increase in the filler content, Seebeck coefficient is more or less constant. Relatively small changes of thermal conductivity can be attributed to the phonon scattering effect in both the carbon black and the thermally insulating PEDOT layers. This study reports that the power factor of the composite was estimated to be 0.993μW/mK2 for 10wt% filler content and was more than 1.7 times higher than that for pure PEDOT, and the maximum figure of merit (ZT) value was 0.0012 at room temperature.

Organic phototransistors using poly(3-hexylthiophene) nanofibres

Here we report the fabrication of nanofibre-based organic phototransistors (OPTs) using preformed poly(3-hexylthiophene) (P3HT) nanofibres. OPT performance is analysed based on two important parameters: photoresponsivity R and photosensitivity P. Before testing the devices as OPTs, the normal organic field-effect transistor (OFET) operation is characterized, revealing a surface-coverage-dependent performance. With R reaching 250 A W−1 in the on-state (VGS = −40 V) and P reaching 6.8 × 103 in the off-state (VGS = 10 V) under white light illumination (Iinc = 0.91 mW cm−2), the best nanofibre-based OPTs outperform the OPTs fabricated from a solution of P3HT in chlorobenzene, in which no preformed fibres are present. The better performance is attributed to an increase in active layer crystallinity, a better layer connectivity and an improved edge-on orientation of the thiophene rings along the polymer backbone, resulting in a longer exciton diffusion length and enhanced charge carrier mobility, linked to a decreased interchain coupling energy. In addition, the increased order in the active layer crystallinity induces a better spectral overlap between the white light emission spectrum and the active layer absorption spectrum, and the absorption of incident light is maximised by the favourable parallel orientation of the polymer chains with respect to the OPT substrate. Combining both leads to an increase in the overall light absorption. In comparison with previously reported solution-processed organic OPTs, it is shown here that no special dielectric surface treatment or post-deposition treatment of the active device layer is needed to obtain high OPT performance. Finally, it is also shown that, inherent to an intrinsic gate-tuneable gain mechanism, changing the gate potential results in a variation of R over at least five orders of magnitude. As such, it is shown that R can be adjusted according to the incident light intensity.

Pulsed laser deposition and optical band gap engineering in multinary transparent conducting oxide thinfilms

Synthesis of ternary and multinary oxide-based films offers the possibility of tuning electrical and optical properties of the existing materials over wide range. Here we report about synthesis and characterization of Zn1.9Sn0.9In0.1Ga0.1O4, Zn1.9Sn0.9In0.2O4, and Zn1.9Sn0.9Ga0.2O4 grown by a pulsed laser deposition method. These compounds have been synthesized on the base of Zn2SnO4 by substituting Zn2+ and Sn4+cations with group-III elements such as In3+ and Ga3+. The newly synthesized films are shown to possess a very smooth surface with lower RMS components and exhibit dense grown crystallites with homogenous distribution of small grains. Highly textured growth of inverse cubic spinel structured thinfilms along (111) direction is identified from X-ray diffraction studies. Raman analysis provided supplementary evidences for XRD results. Giant increases of the band gap from 3.60eV to 3.90eV have been reported by the development of multinary compounds. The electrical features obtained from Van der Pauw Hall measurements show enhanced charge carrier mobility, resistivity and moderate charge carrier concentrations.

Discotic Liquid Crystal‐Functionalized Gold Nanorods: 2‐ and 3D Self‐Assembly and Macroscopic Alignment as well as Increased Charge Carrier Mobility in Hexagonal Columnar Liquid Crystal Hosts Affected by Molecular Packing and π–π Interactions

Gold nanorods functionalized with triphenylene‐based discotic liquid crystal (LC) motifs show striking self‐assembly behavior both on transmission electron microscopy (TEM) grids as well as in the bulk enforced by the π–π‐stacking of triphenylene groups of adjacent nanorods. TEM images confirm that these discotic LC nanorods form ribbons of parallel‐stacked nanorods several hundred nanometer long. The pursued silane conjugation approach to decorate the nanorods allows for the preparation of dispersions of the nanorods in the hexagonal columnar phases of parent discotic LCs, where the nanorods can be macroscopically aligned with almost 80% efficiency by a simple shearing protocol. Doping the parent host materials with about 1% by weight of the discotic LC‐capped nanorods also reduces the lattice parameter and the intracolumnar packing, which gives rise to enhanced charge carrier mobility in these hosts as determined by time‐of‐flight measurements.

Proton intercalated two-dimensional WO3 nano-flakes with enhanced charge-carrier mobility at room temperature.

Quasi two-dimensional (Q2D) semiconducting metal oxides with enhanced charge carrier mobility hold tremendous promise for nano-electronics, photonics, catalysis, nano-sensors and electrochromic applications. In addition to graphene and metal dichalcogenides MX2 (M = Mo, W; X = S, Se, Te), 2D sub-stoichiometric WO(3-x) is gaining importance as a promising semiconductor material for field-effect-transistor (FET) based devices. A combination of high permittivity, suppression of the Coulomb effects, and their stratified structure enhances the carrier mobility in such a material. Additionally, the sub-stoichiometry of this semiconductor oxide allows the reduction of the bandgap and increase of the free charge carriers at the same time. Here, we report for the first time H(+) intercalated WO(3) FETs, made of Q2D nano-flakes, with enhanced charge-carrier mobility exceeding 319 cm(2) V(-1) s(-1) comparable with the charge-carrier mobility of Q2D dichalcogenides MoS(2) and WSe(2). Analyses indicate that the enhanced electrical properties of the sub-stoichiometric WO(3-x) depend on the oxygen vacancies in the intercalated nano-flakes. These findings confirmed that Q2D sub-stoichiometric WO(3-x) is a promising material for various functional FET devices.

2,6-Diphenyl- and -distyryl-capped 3,7-dialkoxybenzo[1,2-b:4,5-b']dithiophenes and their dithieno-annulated higher homologs: structural phase transition with enhanced charge carrier mobility.

Synthesis of the title benzo[1,2-b:4,5-b']dithiophenes was achieved using 2-ethylhexyl 3,7-dihydroxybenzo[1,2-b:4,5-b']dithiophene-2,6-dicarboxylate as the common starting material. The effect of the introduction of phenyl and styryl groups as well as thieno-annulation to the benzo[1,2-b:4,5-b']dithiophene core on π-conjugation was estimated by means of absorption and emission spectrometry and cyclic voltammetry. The phase behaviours of the compounds were also observed by differential scanning calorimetry and the dithieno-annulated higher homologs were found to show a solid-solid (crystalline-crystalline) phase transition. Then, intrinsic charge carrier mobilities in the π-systems were measured by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) method and the values were in the range of 0.04-0.17 cm(2) V(-1) s(-1). Remarkably, the thieno-annulated and phenyl-capped derivative showed a temperature/phase-dependent hole mobility profile with 3-fold increment in the second crystalline phase above 100 °C.