Two‐Dimensional Assembly of Symmetric Colloidal Dimers under Electric Fields

Like atoms and molecules with directional interactions, anisotropic particles could potentially assemble into a much wider range of crystalline arrays and meso‐structures than spherical particles with isotropic interactions. In this paper, the electric‐field directed assembly of geometrically anisotropic particles–colloidal dimers is studied. Rich phase behavior and different assembly regimes are found, primarily arising from the broken radial symmetry in particles. The orientations of individual dimers depend on the frequency of the electric field, the ramping direction of frequency, and the salt concentration. The competition and balance between the hydrodynamic, electric, and Brownian torques determine the orientation of individual particles, while the competition between the electrohydrodynamic force and dipolar interaction determines the aggregation of aligned particles at a given experimental condition. The field distribution near the electrode is critical to understand the orientation and assembly behavior of colloidal dimers on a conducting substrate. This study also demonstrates the effectiveness, the reversibility, and potential opportunity of applying electric field to control the orientation and direct the assembly of non‐spherical particles. In particular, two dimensional close‐packed crystals of perpendicularly aligned dimers are obtained, which shows promise in fabricating 3D photonic crystals based on dimer‐like colloids and field‐directed display.     

High K Capacitors and OFET Gate Dielectrics from Self‐Assembled BaTiO3 and (Ba,Sr)TiO3 Nanocrystals in the Superparaelectric Limit

Nanodielectrics is an emerging field with applications in capacitors, gate dielectrics, energy storage, alternatives to Li‐ion batteries, and frequency modulation in communications devices. Self‐assembly of high k dielectric nanoparticles is a highly attractive means to produce nanostructured films with improved performance—namely dielectric tunability, low leakage, and low loss—as a function of size, composition, and structure. One of the major challenges is conversion of the nanoparticle building block into a reliable thin film device at conditions consistent with integrated device manufacturing or plastic electronics. Here, the development of BaTiO₃ and (Ba,Sr)TiO₃ superparaelectric uniform nanocrystal (8–12 nm) films prepared at room temperature by evaporative driven assembly with no annealing step is reported. Thin film inorganic and polymer composite capacitors show dielectric constants in the tunable range of 10–30, dependent on composition, and are confirmed to be superparaelectric. Organic thin film transistor (TFT) devices on flexible substrates demonstrate the readiness of nanoparticle‐assembled films as gate dielectrics in device fabrication.     

Layer‐by‐Layer Conjugated Extension of a Semiconducting Polymer for High‐Performance Organic Field‐Effect Transistor

A donor–acceptor (D–A) semiconducting copolymer, PDPP‐TVT‐29, comprising a diketopyrrolopyrrole (DPP) derivative with long, linear, space‐separated alkyl side‐chains and thiophene vinylene thiophene (TVT) for organic field‐effect transistors (OFETs) can form highly π‐conjugated structures with an edge‐on molecular orientation in an as‐spun film. In particular, the layer‐like conjugated film morphologies can be developed via short‐term thermal annealing above 150 °C for 10 min. The strong intermolecular interaction, originating from the fused DPP and D–A interaction, leads to the spontaneous self‐assembly of polymer chains within close proximity (with π‐overlap distance of 3.55 Å) and forms unexpectedly long‐range π‐conjugation, which is favorable for both intra‐ and intermolecular charge transport. Unlike intergranular nanorods in the as‐spun film, well‐conjugated layers in the 200 °C‐annealed film can yield more efficient charge‐transport pathways. The granular morphology of the as‐spun PDPP‐TVT‐29 film produces a field‐effect mobility (μ _FET) of 1.39 cm² V^?1 s^?1 in an OFET based on a polymer‐treated SiO₂ dielectric, while the 27‐Å‐step layered morphology in the 200 °C‐annealed films shows high μ _FET values of up to 3.7 cm² V^?1 s^?1.     

Directed Electric Field Z‐Alignment Kinetics of Anisotropic Nanoparticles for Enhanced Ionic Conductivity

In this study, the fast transient evolution of the electric field assisted thickness Z‐direction orientation and assembly of clay particles is studied using a instrumented real time system that simultaneously measures in‐plane and out of plane birefringence. The optical anisotropy master curves are developed, connecting the exposure time and electric field strength with orientation, using a superposition principle. Z‐oriented nanocomposite films manufactured through the R2R process show enhancement through thickness ionic conductivity, useful for membranes of batteries and fuel cells.     

An Orientation‐Controlled Pentacene Film Aligned by Photoaligned Polyimide for Organic Thin‐Film Transistor Applications

We have demonstrated that the photoalignment method could be used to control the structural anisotropy of pentacene films, an active semiconducting layer, in thin‐film transistors (TFTs) with conspicuously anisotropic electrical characteristics. The photoaligned pentacene films were characterized with respect to structure and morphology using X‐ray diffraction and atomic force microscopy. Compared to the pentacene films that are not controlled, a maximal 25‐times increase in field‐effect mobility (up to 0.75 cm V^–1 s^–1) has been achieved in the photoaligned pentacene‐based TFTs by aligning pentacene orientation parallel to the direction of current flow with the help of a photoaligned polyimide layer. Mobility anisotropic ratio in the range of 2.7–8.3 for the current flow parallel and perpendicular to the alignment of the photoaligned pentacene films have been observed for photoaligned pentacene‐based TFTs.     

A Versatile Method to Fabricate Highly In‐Plane Aligned Conducting Polymer Films with Anisotropic Charge Transport and Thermoelectric Properties: The Key Role of Alkyl Side Chain Layers on the Doping Mechanism

A general method is proposed to produce oriented and highly crystalline conducting polymer layers. It combines the controlled orientation/crystallization of polymer films by high‐temperature rubbing with a soft‐doping method based on spin‐coating a solution of dopants in an orthogonal solvent. Doping rubbed films of regioregular poly(3‐alkylthiophene)s and poly(2,5‐bis(3‐dodecylthiophen‐2‐yl)thieno[3,2‐b ]thiophene) with 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄TCNQ) yields highly oriented conducting polymer films that display polarized UV–visible–near‐infrared (NIR) absorption, anisotropy in charge transport, and thermoelectric properties. Transmission electron microscopy and polarized UV–vis–NIR spectroscopy help understand and clarify the structure of the films and the doping mechanism. F₄TCNQ^? anions are incorporated into the layers of side chains and orient with their long molecular axis perpendicular to the polymer chains. The ordering of dopant molecules depends closely on the length and packing of the alkyl side chains. Increasing the dopant concentration results in a continuous variation of unit cell parameters of the doped phase. The high orientation results in anisotropic charge conductivity (σ) and thermoelectric properties that are both enhanced in the direction of the polymer chains (σ = 22 ± 5 S cm^?1 and S = 60 ± 2 µV K^?1). The method of fabrication of such highly oriented conducting polymer films is versatile and is applicable to a large palette of semiconducting polymers.     

Highly Conductive,Bendable, Embedded Ag Nanoparticle Wire Arrays Via Convective Self‐Assembly: Hybridization into Ag Nanowire Transparent Conductors

The optoelectrical properties of Ag nanowire (NW) networks are improved by incorporating the NWs into highly conductive ordered arrays of Ag nanoparticle wires (NPWs) fabricated via surfactant‐assisted convective self‐assembly. The NPW–NW hybrid conductor displays a transmittance (T) of 90% at 550 nm and a sheet resistance (R _s) of 5.7 Ω sq^?1, which is superior to the corresponding properties of the NW network showing a R _s of 14.1 Ω sq^?1 at a similar T. By the modified wettability of a donor substrate and the capillarity of water, the sintered NPW–NW hybrid conductors are perfectly transferred onto an UV‐curable photopolymer film, and the embedded hybrid conductors exhibit excellent electromechanical properties. The R _s and T of the NPW arrays can be predicted by using a simple model developed to calculate the width and height of the hexagonal close‐packed particles formed during the convective self‐assembly. The numerical analysis reveals that the maximum Haacke figure of merit of the NW networks is increased considerably from 0.0260 to 0.0407 Ω^?1 by integration with the NPW array. The highly conductive NPW arrays generated using a simple, low‐cost, and nonlithographic process can be applied to enhancing the performances of other transparent conductors, such as carbon nanotubes, metal oxides, and graphenes.     

A Top Coat with Solvent Annealing Enables Perpendicular Orientation of Sub‐10 nm Microdomains in Si‐Containing Block Copolymer Thin Films

Achieving sub‐10 nm high‐aspect‐ratio patterns from diblock copolymer self‐assembly requires both a high interaction parameter (χ, which is determined by the incompatibility between the two blocks) and a perpendicular orientation of microdomains. However, these two conditions are extremely difficult to achieve simultaneously because the blocks in a high‐χ copolymer typically have very different surface energies, favoring in‐plane microdomain orientations. A fully perpendicular orientation of a high‐χ block copolymer, poly(styrene‐block‐dimethylsiloxane) (PS‐b‐PDMS) is realized here using partially hydrolyzed polyvinyl alcohol (PVA) top coats with a solvent annealing process, despite the large surface energy differences between PS and PDMS. The PVA top coat on the block copolymer films under a solvent vapor atmosphere significantly reduces the interfacial energy difference between two blocks at the top surface and provides sufficient solvent concentration gradient in the through‐thickness direction and appropriate solvent evaporation rates within the film to promote a perpendicular microdomain orientation. The effects of interfacial energy differences and the swellability of PVA top coats controlled by the degree of hydrolysis on the orientation of micro­domains are examined. The thickness of the BCP film and top coats also affects the orientation of the BCP film.     

Electrically Conductive Thin Films Prepared from Layer‐by‐Layer Assembly of Graphite Platelets

Layer‐by‐layer (LBL) assembly of carbon nanoparticles for low electrical contact resistance thin film applications is demonstrated. The nanoparticles consist of irregularly shaped graphite platelets, with acrylamide/ββ‐methacryl‐oxyethyl‐trimethyl‐ammonium copolymer as the cationic binder. Nanoparticle zeta (ζζ) potential and thereby electrostatic interactions are varied by altering the pH of graphite suspension as well as that of the binder suspension. Film thickness as a function of zeta potential, immersion time, and the number of layers deposited is obtained using Monte Carlo simulation of the energy dispersive spectroscopy measurements. Multilayer film surface morphology is visualized via field‐emission scanning electron microscopy and atomic‐force microscopy. Thin film electrical properties are characterized using electrical contact resistance measurements. Graphite nanoparticles are found to self‐assemble onto gold substrates through two distinct yet overlapping mechanisms. The first mechanism is characterized by logarithmic carbon uptake with respect to the number of deposition cycles and slow clustering of nanoparticles on the gold surface. The second mechanism results from more rapid LBL nanoparticle assembly and is characterized by linear weight uptake with respect to the number of deposition cycles and a constant bilayer thickness of 15 to 21 nm. Thin‐film electrical contact resistance is found to be proportional to the thickness after equilibration of the bilayer structure. Measured values range from 1.6 mΩ cm^?2 at 173 nm to 3.5 mΩ cm^?2 at 276 nm. Coating volume resistivity is reduced when electrostatic interactions are enhanced during LBL assembly.     

On the Relation between Morphology and FET Mobility of Poly(3‐alkylthiophene)s at the Polymer/SiO2 and Polymer/Air Interface

The influence of the interface of the dielectric SiO₂ on the performance of bottom‐contact, bottom‐gate poly(3‐alkylthiophene) (P3AT) field‐effect transistors (FETs) is investigated. In particular, the operation of transistors where the active polythiophene layer is directly spin‐coated from chlorobenzene (CB) onto the bare SiO₂ dielectric is compared to those where the active layer is first spin‐coated then laminated via a wet transfer process such that the film/air interface of this film contacts the SiO₂ surface. While an apparent alkyl side‐chain length dependent mobility is observed for films directly spin‐coated onto the SiO₂ dielectric (with mobilities of ≈10^?3 cm² V^?1 s^?1 or less) for laminated films mobilities of 0.14 ± 0.03 cm² V^?1 s^?1 independent of alkyl chain length are recorded. Surface‐sensitive near edge X‐ray absorption fine structure (NEXAFS) spectroscopy measurements indicate a strong out‐of‐plane orientation of the polymer backbone at the original air/film interface while much lower average tilt angles of the polymer backbone are observed at the SiO₂/film interface. A comparison with NEXAFS on crystalline P3AT nanofibers, as well as molecular mechanics and electronic structure calculations on ideal P3AT crystals suggest a close to crystalline polymer organization at the P3AT/air interface of films from CB. These results emphasize the negative influence of wrongly oriented polymer on charge carrier mobility and highlight the potential of the polymer/air interface in achieving excellent “out‐of‐plane” orientation and high FET mobilities.     

High‐Performance n‐Channel Thin‐Film Field‐Effect Transistors Based on a Nanowire‐Forming Polymer

A new electrontransport polymer, poly{[N,N′‐dioctylperylene‐3,4,9,10‐bis(dicarboximide)‐1,7(6)‐diyl]‐alt‐[(2,5‐bis(2‐ethyl‐hexyl)‐1,4‐phenylene)bis(ethyn‐2,1‐diyl]} (PDIC8‐EB), is synthesized. In chloroform, the polymer undergoes self‐assembly, forming a nanowire suspension. The nanowire's optical and electrochemical properties, morphological structure, and field‐effect transistor (FET) characteristics are investigated. Thin films fabricated from a PDIC8‐EB nanowire suspension are composed of ordered nanowires and ordered and amorphous non‐nanowire phases, whereas films prepared from a homogeneous PDIC8‐EB solution consist of only the ordered and amorphous non‐nanowire phases. X‐ray scattering experiments suggest that in both nanowires and ordered phases, the PDIC8 units are laterally stacked in an edge‐on manner with respect to the film plane, with full interdigitation of the octyl chains, and with the polymer backbones preferentially oriented within the film plane. The ordering and orientations are significantly enhanced through thermal annealing at 200 °C under inert conditions. The polymer film with high degree of structural ordering and strong orientation yields a high electron mobility (0.10 ± 0.05 cm² V^?1 s^?1), with a high on/off ratio (3.7 × 10⁶), a low threshold voltage (8 V), and negligible hysteresis (0.5 V). This study demonstrates that the polymer in the nanowire suspension provides a suitable material for fabricating the active layers of high‐performance n‐channel FET devices via a solution coating process.     

Engineering of Self‐Assembled Domain Architectures with Ultra‐high Piezoelectric Response in Epitaxial Ferroelectric Films

Substrate clamping and inter‐domain pinning limit movement of non‐180° domain walls in ferroelectric epitaxial films thereby reducing the resulting piezoelectric response of ferroelectric layers. Our theoretical calculations and experimental studies of the epitaxial PbZr_xTi_1–xO₃ films grown on single crystal SrTiO₃ demonstrate that for film compositions near the morphotropic phase boundary it is possible to obtain mobile two‐domain architectures by selecting the appropriate substrate orientation. Transmission electron microscopy, X‐ray diffraction analysis, and piezoelectric force microscopy revealed that the PbZr_0.52Ti_0.48O₃ films grown on (101) SrTiO₃ substrates feature self‐assembled two‐domain structures, consisting of two tetragonal domain variants. For these films, the low‐field piezoelectric coefficient measured in the direction normal to the film surface (d₃₃) is 200 pm V^–1, which agrees well with the theoretical predictions. Under external AC electric fields of about 30 kV cm^–1, the (101) films exhibit reversible longitudinal strains as high as 0.35 %, which correspond to the effective piezoelectric coefficients in the order of 1000 pm V^–1 and can be explained by elastic softening of the PbZr_xTi_1–xO₃ ferroelectrics near the morphotropic phase boundary.     

Layer‐by‐Layer Synthesis of Thick Mesoporous TiO2 Films with Vertically Oriented Accessible Nanopores and Their Application for Lithium‐Ion Battery Negative Electrodes

TiO₂ films of varying thicknesses (up to ≈1.0 µm) with vertically oriented, accessible 7–9 nm nanopores are synthesized using an evaporation‐induced self‐assembly layer‐by‐layer technique. The hypothesis behind the approach is that epitaxial alignment of hydrophobic blocks of surfactant templates induces a consistent, accessible mesophase orientation across a multilayer film, ultimately leading to continuous, vertically aligned pore channels. Characterization using grazing incidence X‐ray scattering, scanning electron microscopy, and impedance spectroscopy indicates that the pores are oriented vertically even in relatively thick films (up to 1 µm). These films contain a combination of amorphous and nanocrystalline anatase titania of value for electrochemical energy storage. When applied as negative electrodes in lithium‐ion batteries, a capacity of 254 mAh g^?1 is obtained after 200 cycles for a single‐layer TiO₂ film prepared on modified substrate, higher than on unmodified substrate or nonporous TiO₂ film, due to the high accessibility of the vertically oriented channels in the films. Thicker films on modified substrate have increased absolute capacity because of higher mass loading but a reduced specific capacity because of transport limitations. These results suggest that the multilayer epitaxial approach is a viable way to prepare high capacity TiO₂ films with vertically oriented continuous nanopores.     

Determination of crystal orientation in organic thin films using optical microscopy

The electrical behavior of devices based on highly crystalline thin films of organic semiconductors is inherently anisotropic. Thin film optimization requires simple and accessible means to characterize the orientation of the constituent crystals. The standard polarized light microscopy (PLM) provides a contrast between different crystallites but fails to distinguish crystals with relative orientation of 90°. In this paper, we discuss two methods that enable the unambiguous identification of crystal orientation in thin films of optically anisotropic materials: PLM with a full-wave retardation plate and differential interference contrast (DIC). The latter is standard on most microscopes and delivers images with high contrast and good color balance.As an illustration, we use DIC to extract the optical properties of highly crystalline thin films of three high-performance organic semiconductors: rubrene, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C₈-BTBT). Building on the relation between optical properties and crystal orientation, we demonstrate how DIC characterizes the in-plane crystal orientation of these thin films. This leads to the identification of the fast growth direction of the crystal front.     

Fabrication and Electrochemical Properties of Epitaxial Samarium‐Doped Ceria Films on SrTiO3‐Buffered MgO Substrates

Thin films of samarium‐oxide‐doped (20 mol%) ceria (SDC) are grown by pulsed‐laser deposition (PLD) on (001) MgO single‐crystal substrates. SrTiO₃ (STO) prepared by PLD is used as a buffer layer on the MgO substrates to enable epitaxial growth of the fluorite‐structured SDC film; the STO layer provides a proper crystalline match between SDC and MgO, resulting in highly crystalline, epitaxial SDC films grown in the (001) orientation. Film conductivity is evaluated by electrochemical impedance spectroscopy measurements, which are performed at various temperatures (400–775 °C) in a wide range of oxygen partial pressure (pO₂) values (10^?25?1 atm) in order to separate ionic and electronic conductivity contributions. At 700 °C, SDC/STO films on (100) MgO exhibit a dominant ionic conductivity of about 7 × 10^?2 S cm^?1, down to pO₂ values of about 10^?15 atm. The absence of grain boundaries make the SDC/STO/MgO heterostructures stable to oxidation‐reduction cycles at high temperatures, in contrast to that observed for the more disordered SDC/STO films, which degraded after hydrogen exposure.     

Porous Nanofilm Biomaterials Via Templated Layer‐by‐Layer Assembly

Hydrogel‐like biomaterials are often too soft to support robust cell adhesion, yet methods to increase mechanical rigidity (e.g., covalent cross‐linking the gel matrix) can compromise bioactivity by suppressing the accessibility or activity of embedded biomolecules. Nanoparticle templating is reported here as a strategy toward porous, layer‐by‐layer assembled, thin polyelectrolyte films of sufficient mechanical rigidity to promote strong initial cell adhesion, and that are capable of high bioactive species loading. Latex nanoparticles are incorporated during layer‐by‐layer assembly, and following 1‐ethyl‐3‐[3‐dimethylaminopropyl]carbodiimide/N‐hydroxysulfosuccinimide (EDC‐NHS) cross‐linking of the polyelectrolyte film, are removed via exposure to tetrahydrofuran (THF). THF exposure results in only a partial reduction in film thickness (as observed by ellipsometry), suggesting the presence of internal pore space. The attachment, spreading, and metabolic activity of pre‐osteoblastic MC3T3‐E1 cells cultured on templated, cross‐linked films are statistically similar to those on non‐templated films, and much greater than those on non‐cross‐linked films. Laser scanning confocal microscopy and quartz crystal microgravimetry indicate a high capacity for bioactive species loading (ca. 10% of film mass) in nanoparticle templated films. Porous nanofilm biomaterials, formed via layer‐by‐layer assembly with nanoparticle templating, promote robust cell adhesion and exhibit high bioactive species loading, and thus appear to be excellent candidates for cell‐contacting applications.     

The Role of Morphology in Optically Switchable Transistors Based on a Photochromic Molecule/p‐Type Polymer Semiconductor Blend

The correlation between morphology and optoelectronic performance in organic thin‐film transistors based on blends of photochromic diarylethenes (DAE) and poly(3‐hexylthiophene) (P3HT) is investigated by varying molecular weight (M_w = 20–100 kDa) and regioregularity of the conjugated polymer as well as the temperature of thermal annealing (rt‐160 °C) in thin films. Semicrystalline architectures of P3HT/DAE blends comprise crystalline domains, ensuring efficient charge transport, and less aggregated regions, where DAEs are located as a result of their spontaneous expulsion from the crystalline domains during the self‐assembly. The best compromise between field‐effect mobility (μ) and switching capabilities is observed in blends containing P3HT with M_w = 50 kDa, exhibiting μ as high as 1 × 10^?3 cm² V^?1 s^?1 combined with a >50% photoswitching ratio. Higher or lower M_w than 50 kDa are found to be detrimental for field‐effect mobility and to lead to reduced device current switchability. The microstructure of the regioregular P3HT blend is found to be sensitive to the thermal annealing temperature, with an increase in μ and a decrease in current modulation being observed as a response to the light‐stimulus likely due to an increased P3HT‐DAE segregation, partially hindering DAE photoisomerization. The findings demonstrate the paramount importance of fine tuning the structure and morphology of bicomponent films for leveraging the multifunctional nature of optoelectronic devices.     

Self‐Organization of Ink‐jet‐Printed Triisopropylsilylethynyl Pentacene via Evaporation‐Induced Flows in a Drying Droplet

We have demonstrated the influence of evaporation‐induced flow in a single droplet on the crystalline microstructure and film morphology of an ink‐jet‐printed organic semiconductor, 6,13‐bis((triisopropylsilylethynyl) pentacene (TIPS_PEN), by varying the composition of the solvent mixture. The ringlike deposits induced by outward convective flow in the droplets have a randomly oriented crystalline structure. The addition of dichlorobenzene as an evaporation control agent results in a homogeneous film morphology due to slow evaporation, but the molecular orientation of the film is undesirable in that it is similar to that of the ring‐deposited films. However, self‐aligned TIPS_PEN crystals with highly ordered crystalline structures were successfully produced when dodecane was added. Dodecane has a high boiling point and a low surface tension, and its addition to the solvent results in a recirculation flow in the droplets that is induced by a Marangoni flow (surface‐tension‐driven flow), which arises during the drying processes in the direction opposite to the convective flow. The field‐effect transistors fabricated with these self‐aligned crystals via ink‐jet printing exhibit significantly improved performance with an average effective field‐effect mobility of 0.12 cm² V^–1 s^–1. These results demonstrate that with the choice of appropriate solvent ink‐jet printing is an excellent method for the production of organic semiconductor films with uniform morphology and desired molecular orientation for the direct‐write fabrication of high‐performance organic electronics.     

Ultrathin,Organic, Semiconductor/Polymer Blends by Scanning Corona‐Discharge Coating for High‐Performance Organic Thin‐Film Transistors

A new thin‐film coating process, scanning corona‐discharge coating (SCDC), to fabricate ultrathin tri‐isopropylsilylethynyl pentacene (TIPS‐PEN)/amorphous‐polymer blend layers suitable for high‐performance, bottom‐gate, organic thin‐film transistors (OTFTs) is described. The method is based on utilizing the electrodynamic flow of gas molecules that are corona‐discharged at a sharp metallic tip under a high voltage and subsequently directed towards a bottom electrode. With the static movement of the bottom electrode, on which a blend solution of TIPS‐PEN and an amorphous polymer is deposited, SCDC provides an efficient route to produce uniform blend films with thicknesses of less than one hundred nanometers, in which the TIPS‐PEN and the amorphous polymer are vertically phase‐separated into a bilayered structure with a single‐crystalline nature of the TIPS‐PEN. A bottom‐gate field‐effect transistor with a blend layer of TIPS‐PEN/polystyrene (PS) (90/10 wt%) operated at ambient conditions, for example, indeed exhibits a highly reliable device performance with a field‐effect mobility of approximately 0.23 cm² V^?1 s^?1: two orders of magnitude greater than that of a spin‐coated blend film. SCDC also turns out to be applicable to other amorphous polymers, such as poly(α‐methyl styrene) and poly(methyl methacrylate) and, readily combined with the conventional transfer‐printing technique, gives rise to micropatterned arrays of TIPS‐PEN/polymer films.     

Favorable Molecular Orientation Enhancement in Semiconducting Polymer Assisted by Conjugated Organic Small Molecules

A bimodal texturing effect of semiconducting polymers is investigated by incorporating conjugated small molecules to significantly improve the charge transport characteristics via formation of 3D transport pathways. Solution blending of the electron‐transporting polymer, poly{[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)} (P(NDI2OD‐T2)), with small molecular crystals of tetrathiafulvalene and tetracyanoquinodimethane is used, and the thin film microstructures are studied using a combination of atomic force microscopy, transmission electron microscopy, 2D grazing incidence X‐ray diffraction, and surface‐sensitive near‐edge X‐ray absorption fine structure. Blended thin films show edge‐on and face‐on bimodal texture with long‐range order and microstructure packing orientation preferable for electron transport through the channel in organic field‐effect transistors, which is confirmed by high electron mobility 1.91 cm² V^?1 s^?1, small contact resistance, and low energetic disorder according to temperature dependence of the field‐effect mobility. Structural changes suggest a 3D network charge transport model via lamella packing and bimodal orientation of the semiconducting polymers.