Spontaneous Patterning of High-Resolution Electronics via Parallel Vacuum Ultraviolet

High-Performance Flexible Electronics Fabricated Using a Surface Energy-Directed Assembly Process on Ultrathin Polyimide Substrates

Solution-based processes are emerging in the fabrication of flexible electronics owing to their cost-effectiveness, low-temperature processing capabilities, and vacuum-free operations. Currently, printing techniques, as the most widely used solution-based processes, suffer from low resolution and poor pattern fidelity. Although surface energy-directed assembly (SEDA) process enables unparalleled resolution and fidelity, multilayer fabrication and application on flexible substrates are rarely attempted. Here, a SEDA process is used for fabricating metal oxide thin film transistors (TFTs) on ultrathin and flexible polyimide (PI) substrates with a thickness of ≈35 µm. Comprehensive procedures to render PI substrates hydrophobic as well as to homogenize the hydrophobicity of the PI substrates and as-assembled layers are developed. All-solution-processed flexible TFTs are constructed by assembling indium oxide semiconducting channels, indium tin oxide source/drain electrodes, aluminum oxide gate dielectric layers, and indium tin oxide gate electrodes ordinally. The metal oxide TFTs exhibit excellent electrical properties with an average mobility of 22.01 cm2 V-1 s-1 and stable operation under mechanical strain. Flexible inverters with a high voltage gain of 78 and a high dynamic operation frequency of up to 1 kHz are also constructed, representing new opportunities of the SEDA process for the fabrication of next-generation flexible electronics.

Solution-processed high-k photopatternable polymers for low-voltage electronics

High dielectric constant (k) polymers have been widely explored for flexible, low-power-consumption electronic devices. In this work, solution-processable high-k polymers were designed and synthesized by ultraviolet (UV) triggered crosslinking at a low temperature (60 °C). The highly crosslinked network allows for high resistance to organic solvents and high breakdown strength over 2 MV cm-1. The UV-crosslinking capability of the polymers enables them to achieve a high-resolution pattern with a feature size down to 1 μm. Further investigation suggests that the polar cyano pendants in side chains are responsible for increasing the dielectric constant up to 10 in a large-area device array, thereby contributing to a low driving voltage of 5 V and high field-effect mobility exceeding 20 cm2 V-1 s-1 in indium gallium zinc oxide (IGZO) thin-film transistors (TFTs). In addition, the solution-processable high-k dielectric polymers were utilized to fabricate flexible low-voltage organic TFTs, which show highly reliable and reproducible mechanical stability at a bending radius of 5 mm after 1000 cycles. And also, the high radiation stability of the dielectric polymers was observed in a UV-sensitive TFT device, thereby achieving highly reproducible pattern recognition, which is promising for artificial optic nerve circuits.

Characterization of Particle Transport and Deposition Due to Heterogeneous Dewetting on Low-Cost Inkjet-Printed Devices

This work investigates the deposition patterns left by evaporating particle-laden droplets on heterogeneous surfaces with spatially varying wettability. Spatial differences in receding contact angles give rise to scalloped-shaped contact lines. During evaporation, the contact line recedes in one location and remains pinned in another. This nonuniform contact line recession results in particle self-assembly above areas where the contact line remains pinned but not where it recedes. This behavior is fairly robust across a variety of particle sizes, concentrations, and device geometries. We hypothesize that particle self-assembly in these cases is due to the competition between particle diffusion and evaporative-driven advective flow. Diffusion appears to be more pronounced in regions where the contact line recedes, while advection appears to be more pronounced near the pinned portion of the contact line. As such, particles appear to diffuse away from receding areas and toward pinned areas, where advection transports them to the contact line. The distribution of particle deposition above the pinned regions was influenced by the particle size and the concentration of particles in the droplet. Similar to homogeneous surfaces, deposition was more prevalent at the pinned portion of the contact line for smaller particles and lower concentrations and more uniformly distributed across the entire pinned region for larger particles and higher concentrations. A better understanding of this process may be beneficial in a wide variety of particle separation applications, such as printing, cell patterning, biosensing, and anti-icing.

Ultrahigh-resolution quantum dot patterning for advanced optoelectronic devices

Quantum dots have attracted significant scientific interest owing to their optoelectronic properties, which are distinct from their bulk counterparts. In order to fully utilize quantum dots for next generation devices with advanced functionalities, it is important to fabricate quantum dot colloids into dry patterns with desired feature sizes and shapes with respect to target applications. In this review, recent progress in ultrahigh-resolution quantum dot patterning technologies will be discussed, with emphasis on the characteristic advantages as well as the limitations of diverse technologies. This will provide guidelines for selecting suitable tools to handle quantum dot colloids throughout the fabrication of quantum dot based solid-state devices. Additionally, epitaxially fabricated single-particle level quantum dot arrays are discussed. These are extreme in terms of pattern resolution, and expand the potential application of quantum dots to quantum information processing.

Ink-Drop Dynamics on Chemically Modified Surfaces

Inkjet printing provides an efficient routine for distributing functional materials into locations with well-designed arrangements. As one of the most critical factors in determining the printing quality, the impacting and depositing behaviors of ink drops largely depend on the wettability of the target surface. In addition to printing on solids with intrinsic wettability, various ink-drop impact dynamics and deposition morphologies have been reported through modifying the surface wettability including both homogeneous and heterogeneous, which opens up possibilities for applications such as advanced optic/electric device fabrication and highly sensitive detection. In this Perspective, we summarize recent progress in the modification methods of solid surface wettability and their capability in modulating the ink-drop impacting and depositing dynamics. The challenges facing ink-drop regulation by chemical modification methodologies are also envisaged at the end of the Perspective.

Patterning Wettability for Open-Surface Fluidic Manipulation: Fundamentals and Applications

Effective manipulation of liquids on open surfaces without external energy input is indispensable for the advancement of point-of-care diagnostic devices. Open-surface microfluidics has the potential to benefit health care, especially in the developing world. This review highlights the prospects for harnessing capillary forces on surface-microfluidic platforms, chiefly by inducing smooth gradients or sharp steps of wettability on substrates, to elicit passive liquid transport and higher-order fluidic manipulations without off-the-chip energy sources. A broad spectrum of the recent progress in the emerging field of passive surface microfluidics is highlighted, and its promise for developing facile, low-cost, easy-to-operate microfluidic devices is discussed in light of recent applications, not only in the domain of biomedical microfluidics but also in the general areas of energy and water conservation.

Noninvasive and Direct Patterning of High-Resolution Full-Color Quantum Dot Arrays by Programmed Microwetting

Although the commercialization of electroluminescent quantum-dot (QD) displays essentially demands multicolor patterning of QDs with sufficient scalability and uniformity, the implementation of QD patterning in a light-emitting diode device is highly challenging, mainly due to the innate vulnerability of QDs and charge-transport layers. Here, we introduce a noninvasive surface-wetting approach for patterning full-color QD arrays on a photoprogrammed hole-transport layer (HTL). To achieve noninvasiveness of QD patterning, surface-specific modification of HTLs was performed without degrading their performance. Moreover, engineering the solvent evaporation kinetics allows area-selective wetting of QD patterns with a uniform thickness profile. Finally, multicolor QD patterning was enabled by preventing cross-contamination between different QD colloids via partial fluoro-encapsulation of earlier-patterned QDs. Throughout the overall QD patterning process, the optoelectronic properties of QDs and hole-transport layers are well preserved, and prototype electroluminescent quantum dot light-emitting diode arrays with high current efficiency and brightness were realized.

Rapid Assembly of Cellulose Microfibers into Translucent and Flexible Microfluidic Paper-Based Analytical Devices via Wettability Patterning

Microfluidic paper-based analytical devices (μPADs) are emerging as powerful analytical platforms in clinical diagnostics, food safety, and environmental protection because of their low cost and favorable substrate properties for biosensing. However, the existing top-down fabrication methods of paper-based chips suffer from low resolution (>200 μm). Additionally, papers have limitations in their physical properties (e.g., thickness, transmittance, and mechanical flexibility). Here, we demonstrate a bottom-up approach for the rapid fabrication of heterogeneously controlled paper-based chip arrays. We simply print a wax-patterned microchip with wettability contrasts, enabling automatic and selective assembly of cellulose microfibers to construct predefined paper-based microchip arrays with controllable thickness. This paper-based microchip printing technology is feasible for various substrate materials ranging from inorganic glass to organic polymers, providing a versatile platform for the full range of applications including transparent devices and flexible health monitoring. Our bottom-up printing technology using cellulose microfibers as the starting material provides a lateral resolution down to 42 ± 3 μm and achieves the narrowest channel barrier down to 33 ± 2 μm. As a proof-of-concept demonstration, a flexible paper-based glucose monitor is built for human health care, requiring only 0.3 μL of sample for testing.

Site-selective growth of two-dimensional materials: strategies and applications

Over the years, there have been major advances in two-dimensional (2D) materials on account of their excellent and unique properties. Among the various strategies for 2D material fabrication, chemical vapor deposition (CVD) is considered as the most promising method to achieve large-area and high-quality 2D film growth. Furthermore, to realize the potential applications of 2D materials in different fields, the integration of 2D materials into functional devices is essential. However, the materials made by common CVD are randomly distributed on substrates, which is disadvantageous for fabricating arrays of devices. To solve this problem, a site-selective growth method was developed to meet the requirement of batch production for practical applications because it achieves control over the locations of products and benefits the subsequent direct integration. Herein, state-of-the-art methods for site-selective synthesis, including seeded growth and patterned growth, are reviewed. Then, the electronic and optoelectronic applications of the as-grown 2D materials are also reviewed. Finally, the remaining challenges and future prospects regarding site-selective methods and applications are discussed.

Layer-By-Layer Printing Strategy for High-Performance Flexible Electronic Devices with Low-Temperature Catalyzed Solution-Processed SiO2

Additive printing techniques have been widely investigated for fabricating multilayered electronic devices. In this work, a layer-by-layer printing strategy is developed to fabricate multilayered electronics including 3D conductive circuits and thin-film transistors (TFTs) with low-temperature catalyzed, solution-processed SiO₂ (LCSS) as the dielectric. Ultrafine, ultrasmooth LCSS films can be facilely formed at 90 °C on a wide variety of organic and inorganic substrates, offering a versatile platform to construct complex heterojunction structures with layer-by-layer fashion at microscale. The high-resolution 3D conductive circuits formed with gold nanoparticles inside the LCSS dielectric demonstrate a high-speed response to the transient voltage in less than 1 µs. The TFTs with semiconducting single-wall carbon nanotubes can be operated with the accumulation mode at a low voltage of 1 V and exhibit average field-effect mobility of 70 cm²  V^-1  s^-1 , on/off ratio of 10⁷ , small average hysteresis of 0.1 V, and high yield up to 100% as well as long-term stability, high negative-gate bias stability, and good mechanical stability. Therefore, the layer-by-layer printing strategy with the LCSS film is promising to assemble large-scale, high-resolution, and high-performance flexible electronics and to provide a fundamental understanding for correlating dielectric properties with device performance.

Rapid generation of hybrid biochemical/mechanical cues in heterogeneous droplets for high-throughput screening of cellular responses

Cells in their native microenvironment are subjected to varying combinations of biochemical cues and mechanical cues in a wide range. Although many signaling pathways have been found to be responsive for extracellular cues, little is known about how biochemical cues crosstalk with mechanical cues in a complex microenvironment. Here, we introduced heterogeneous droplets on a microchip, which were rapidly assembled by combining wettability-patterned microchip and programmed droplet manipulations, for a high-throughput cell screening of the varying combinations of biochemical cues and mechanical cues. This platform constructed a heterogeneous droplet/microgel array with orthogonal gradual chemicals and materials, which was further applied to analyze the cellular Wnt/β-catenin signaling in response to varying combinations of Wnt ligands and substrate stiffness. Thus, this device provides a powerful multiplexed bioassay platform for drug development, tissue engineering, and stem cell screening.

Dual Surface Architectonics for Directed Self-Assembly of Ultrahigh-Resolution Electronics

The directed self-assembly of electronic circuits using functional metallic inks has attracted intensive attention because of its high compatibility with extensive applications ranging from soft printed circuits to wearable devices. However, the typical resolution of conventional self-assembly technologies is not sufficient for practical applications in the rapidly evolving additively manufactured electronics (AMEs) market. Herein, an ultrahigh-resolution self-assembly strategy is reported based on a dual-surface-architectonics (DSA) process. Inspired by the Tokay gecko, the approach is to endow submicrometer-scale surface regions with strong adhesion force toward metallic inks via a series of photoirradiation and chemical polarization treatments. The prepared DSA surface enables the directed self-assembly of electronic circuits with unprecedented 600 nm resolution, suppresses the coffee-ring effect, and results in a reliable conductivity of 14.1 ± 0.6 µΩ cm. Furthermore, the DSA process enables the layer-by-layer fabrication of fully printed organic thin-film transistors with a short channel length of 1 µm, which results in a large on-off ratio of 10⁶ and a high field-effect mobility of 0.5 cm²  V^-1  s^-1 .

Recent Advancement of Emerging Nano Copper-Based Printable Flexible Hybrid Electronics

Printed copper materials have been attracting significant attention prominently due to their electric, mechanical, and thermal properties. The emerging copper-based flexible electronics and energy-critical applications rely on the control of electric conductivity, current-carrying capacity, and reliability of copper nanostructures and their printable ink materials. In this review, we describe the growth of copper nanostructures as the building blocks for printable ink materials on which a variety of conductive features can be additively manufactured to achieve high electric conductivity and stability. Accordingly, the copper-based flexible hybrid electronics and energy-critical devices printed by different printing techniques are reviewed for emerging applications.

Fluorescence Switchable Conjugated Polymer Microdisk Arrays by Cosolvent Vapor Annealing

Depositing minute light emitters into a regular array is a basic but essential technique in display technology. However, conventional lithographic methodologies involve multistep and energy-consuming processes. Here, we develop a facile method in which organic and polymeric fluorescent dyes spontaneously aggregate to form a patterned microarray. We find that a thin film of fluorescent π-conjugated polymer transforms into micrometer-sized aggregates when exposed to binary organic vapor at ambient temperature. The arrayed microaggregates can be formed over the whole substrate surface when using a quartz substrate that is prepatterned with regular hydrophilic boxes and hydrophobic grids. The resultant microarray is applicable to optical memories and displays when photoswitchable fluorophores are doped into the polymer matrix.

Observation of Wetting Behavior with Ultralow Contact Angle by a Total Reflection and Interference Fringe Method

In order to study the wetting behavior of a liquid film on a surface with ultralow contact angle, the interference fringe method with oblique upward laser is developed. This method allows us to detect the position of contact line precisely and observe the surface profile of very thin film. The contact angle measurement is verified within from 0.007° to 3°. The wetting behavior of silicone oil droplet on a glass substrate is observed. The wetting process can be distinguished with three stages, such as advancing, stable ,and receding stage. In the stable stage, there are two angles near the contact line. And the two angles have opposite variations in trend. It can be seen that there are some reciprocating changes in the two angles and the thickness of the liquid film near the contact line during the stable stage, like the edge of the surf.

Patterning a Superhydrophobic Area on a Facile Fabricated Superhydrophilic Layer Based on an Inkjet-Printed Water-Soluble Polymer Template

An elaborated surface with a superhydrophilic area and a superhydrophobic area was fabricated by inkjet printing a water-soluble polymer template on a superhydrophilic layer. Titanate was used to generate the superhydrophilic layer with an in situ reaction. A water-soluble polymer template was inkjet printed on the facile fabricated superhydrophilic layer. Superhydrophobic treatment was carried out on the inkjet-printed surface with perfluorinated molecules. A superhydrophilic-superhydrophobic patterned surface (SSPS) was obtained by washing out the water-soluble polymer template. Various patterns of SSPS were fabricated with the different water-soluble polymer templates. Then, adhesion and deposition of water droplets were studied on the SSPS with the different wetting abilities on the surface. Meanwhile, a microreaction with a microfluidic chip was realized on the SSPS. In this work, systematic research on fabricating an SSPS based on a facile fabricated superhydrophilic layer with an inkjet-printed water-soluble polymer template is presented. It will have great potential for patterning materials, fabricating devices, and researching interfaces, such as microdroplet self-removal, analyte enrichment, and liquid-liquid interface reaction.

Fabricating High-Resolution Metal Pattern with Inkjet Printed Water-Soluble Sacrificial Layer

The metal pattern plays a crucial role in various optoelectronic devices. However, fabrication of high-resolution metal patterns has serious problems including complicated techniques and high cost. Herein, an inkjet printed water-soluble sacrificial layer was proposed to fabricate a high-resolution metal pattern. The water-soluble sacrificial layer was inkjet printed on a polyethylene glycol terephthalate (PET) surface, and then the printed surface was deposited with a metal layer by evaporating deposition. When the deposited surface was rinsed by water, the metal layer deposited on the water-soluble sacrificial layer could be removed. Various high-resolution metal patterns were prepared, which could be used in electroluminescent displays, strain sensors, and 3D switches. This facile method could be a promising approach for fabricating high-resolution metal patterns.

Fine printing method of silver nanowire electrodes with alignment and accumulation

One-dimensional metal nanowires offer great potential in printing transparent electrodes for next-generation optoelectronic devices such as flexible displays and flexible solar cells. Printing fine patterns of metal nanowires with widths <100 μm is critical for their practical use in the devices. However, the fine printing of metal nanowires onto polymer substrates remains a major challenge owing to their unintended alignment. This paper reports on a fine-printing method for transparent silver nanowires (AgNWs) electrodes miniaturized to a width of 50 μm on ultrathin (1 μm) polymer substrate, giving a high yield of >90%. In this method, the AgNW dispersion, which is swept by a glass rod, is spontaneously deposited to the hydrophilic areas patterned on a hydrophobic-coated substrate. The alignment and accumulation of AgNWs at the pattern periphery are enhanced by employing a high sweeping rate of >3.2 mm s^-1, improving electrical conductivity and pattern definition. The more aligned and more accumulated AgNWs lower the sheet resistance by a factor of up to 6.8. In addition, a high pattern accuracy ≤ 3.6 μm, which is the deviation from the pattern designs, is achieved. Quantitative analyses are implemented on the nanowire alignment to understand the nanowire geometry. This fine-printing method of the AgNW electrodes will provide great opportunities for realizing flexible and high-performance optoelectronic devices.

Wafer-scale and deterministic patterned growth of monolayer MoS2via vapor-liquid-solid method

Vapor transportation is the core process in growing transition-metal dichalcogenides (TMDCs) by chemical vapor deposition (CVD). One inevitable problem is the spatial inhomogeneity of vapors. The non-stoichiometric supply of transition-metal precursors and chalcogens leads to poor control in the products' location, morphology, crystallinity, uniformity and batch to batch reproducibility. The vapor-liquid-solid (VLS) growth method often involves molten precursors (e.g., non-volatile Na2MoO4) at growth temperatures higher than their melting points. The liquid Na2MoO4 can precipitate out solid MoS2 monolayers when saturated with sulfur vapor. Taking advantage of the VLS growth, we attained three kinds of important achievements: (i) a 4-inch-wafer-scale uniform growth of MoS2 flakes on SiO2/Si substrates, (ii) a 2-inch-wafer-scale growth of continuous MoS2 film with the grain size exceeding 100 μm on sapphire substrates, and (iii) a patterned (site-controlled) growth of MoS2 flakes and films. We clarified that the VLS growth thus paves a new way for the high-efficient and scalable synthesis of two-dimensional TMDC monolayers.

Scalable Fabrication of Highly Crystalline Organic Semiconductor Thin Film by Channel-Restricted Screen Printing toward the Low-Cost Fabrication of High-Performance Transistor Arrays

Control over the morphology and crystallinity of small-molecule organic semiconductor (OSC) films is of key importance to enable high-performance organic optoelectronic devices. However, such control remains particularly challenging for solution-processed OSC devices because of the complex crystallization kinetics of small-molecule OSC materials in the dynamic flow of inks. Here, a simple yet effective channel-restricted screen-printing method is reported, which uses small-molecule OSCs/insulating polymer to yield large-grained small-molecule OSC thin-film arrays with good crystallization and preferred orientation. The use of cross-linked organic polymer banks produces a confinement effect to trigger the outward convective flow at two sides of the channel by the fast solvent evaporation, which imparts the transport of small-molecule OSC solutes and promotes the growth of small-molecule OSC crystals parallel to the channel. The small-molecule OSC thin-film array produced by screen printing exhibits excellent performance characteristics with an average mobility of 7.94 cm² V^-1 s^-1 and a maximum mobility of 12.10 cm² V^-1 s^-1 , which are on par with its single crystal. Finally, screen printing can be carried out using a flexible substrate, with good performance. These demonstrations bring this robust screen-printing method closer to industrial application and expand its applicability to various flexible electronics.

Spontaneous Additive Nanopatterning from Solution Route Using Selective Wetting

Nanopatterns of functional materials have successfully led innovations in a wide range of fields, but further exploration of their full potential has often been limited because of complex and cost-inefficient patterning processes. We here propose an additive nanopatterning process of functional materials from solution route using selective wetting phenomenon. The proposed process can produce nanopatterns as narrow as 150 nm with high yield over large area at ultrahigh process speed, that is, the speed of solution dragging, of up to ca. 4.6 m·min^-1. The process is highly versatile that it can utilize a wide range of solution materials, control vertical structures including pattern thickness and multistacks, and produce nanopatterns on various substrates with emerging form factors such as foldability and disposability. The solution patterning in nanoscale by selective wetting is enabled by corresponding surface energy patterns in high contrast that are achieved by one-step imprinting onto hydrophobic/hydrophilic bilayers. The mechanisms and control parameters for the solution patterning are revealed by fluid-dynamic simulation. With the aforementioned advantages, we demonstrate 25 400 pixel-per-inch light-emitting pixel arrays and a plasmonic color filter of 10 cm × 10 cm area on a plastic substrate as potential applications.

3D Printing of Bioinspired Liquid Superrepellent Structures

Bioinspired re-entrant structures have been proved to be effective in achieving liquid superrepellence (including anti-penetration, anti-adhesion, and anti-spreading). However, except for a few reports relying on isotropic etching of silicon wafers, most fluorination-dependent surfaces are still unable to repel liquids with extreme low surface energy (i.e., γ < 15 mN m^-1 ), especially those fluorinated solvents. Herein, triply re-entrant structures, possessing superrepellence to water (with surface tension γ of 72.8 mN m^-1 ) and various organic liquids (γ = 12.0-27.1 mN m^-1 ), are fabricated via two-photon polymerization based 3D printing technology. Such structures can be constructed both on rigid and flexible substrates, and the liquid superrepellent properties can be kept even after oxygen plasma treatment. Based on the prepared triply re-entrant structures, micro open capillaries are constructed on them to realize directional liquid spreading, which may be applied in microfluidic platforms and lab-on-a-chip applications. The fabricated arrays can also find potential applications in electronic devices, gas sensors, microchemical/physical reactors, high-throughput biological sensors, and optical displays.

Uniaxial Alignment of Conjugated Polymer Films for High-Performance Organic Field-Effect Transistors

Polymer semiconductors have been experiencing a remarkable improvement in electronic and optoelectronic properties, which are largely related to the recent development of a vast library of high-performance, donor-acceptor copolymers showing alternation of chemical moieties with different electronic affinities along their backbones. Such steady improvement is making conjugated polymers even more appealing for large-area and flexible electronic applications, from distributed and portable electronics to healthcare devices, where cost-effective manufacturing, light weight, and ease of integration represent key benefits. Recently, a strong boost to charge carrier mobility in polymer-based field-effect transistors, consistently achieving the range from 1.0 to 10 cm² V^-1 s^-1 for both holes and electrons, has been given by uniaxial backbone alignment of polymers in thin films, inducing strong transport anisotropy and favoring enhanced transport properties along the alignment direction. Herein, an overview on this topic is provided with a focus on the processing-structure-property relationships that enable the controlled and uniform alignment of polymer films over large areas with scalable processes. The key aspects are specific molecular structures, such as planarized backbones with a reduced degree of conformational disorder, solution formulation with controlled aggregation, and deposition techniques inducing suitable directional flow.

Printable and Flexible Copper-Silver Alloy Electrodes with High Conductivity and Ultrahigh Oxidation Resistance

Printable and flexible Cu-Ag alloy electrodes with high conductivity and ultrahigh oxidation resistance have been successfully fabricated by using a newly developed Cu-Ag hybrid ink and a simple fabrication process consisting of low-temperature precuring followed by rapid photonic sintering (LTRS). A special Ag nanoparticle shell on a Cu core structure is first created in situ by low-temperature precuring. An instantaneous photonic sintering can induce rapid mutual dissolution between the Cu core and the Ag nanoparticle shell so that core-shell structures consisting of a Cu-rich phase in the core and a Ag-rich phase in the shell (Cu-Ag alloy) can be obtained on flexible substrates. The resulting Cu-Ag alloy electrode has high conductivity (3.4 μΩ·cm) and ultrahigh oxidation resistance even up to 180 °C in an air atmosphere; this approach shows huge potential and is a tempting prospect for the fabrication of highly reliable and cost-effective printed electronic devices.

Spatially Uniform Thin-Film Formation of Polymeric Organic Semiconductors on Lyophobic Gate Insulator Surfaces by Self-Assisted Flow-Coating

Surface hydrophobization by self-assembled monolayer formation is a powerful technique for improving the performance of organic field-effect transistors (OFETs). However, organic thin-film formation on such a surface by solution processing often fails due to the repellent property of the surface against common organic solvents. Here, a scalable unidirectional coating technique that can solve this problem, named self-assisted flow-coating, is reported. Producing a specially designed lyophobic-lyophilic pattern on the lyophobic surface enables organic thin-film formation in the lyophobic surface areas by flow-coating. To demonstrate the usefulness of this technique, OFET arrays with an active layer of poly(2,5-bis(3-hexadecylthiophene-2-yl)thieno[3,2-b]thiophene) are fabricated. The ideal transfer curves without hysteresis behavior are obtained for all OFETs. The average field-effect hole mobility in the saturation regime is 0.273 and 0.221 cm²·V^-1·s^-1 for the OFETs with the channels parallel and perpendicular to the flow-coating direction, respectively, and the device-to-device variation is less than 3% for each OFET set. Very small device-to-device variation is also obtained for the on-state current, threshold voltage, and subthreshold swing. These results indicate that the self-assisted flow-coating is a promising coating technique to form spatially uniform thin films of polymeric organic semiconductors on lyophobic gate insulator surfaces.

Controlled Growth of Large-Area Aligned Single-Crystalline Organic Nanoribbon Arrays for Transistors and Light-Emitting Diodes Driving

ABSTRACT

Organic field-effect transistors (OFETs) based on organic micro-/nanocrystals have been widely reported with charge carrier mobility exceeding 1.0 cm² V^-1 s^-1, demonstrating great potential for high-performance, low-cost organic electronic applications. However, fabrication of large-area organic micro-/nanocrystal arrays with consistent crystal growth direction has posed a significant technical challenge. Here, we describe a solution-processed dip-coating technique to grow large-area, aligned 9,10-bis(phenylethynyl) anthracene (BPEA) and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) single-crystalline nanoribbon arrays. The method is scalable to a 5 × 10 cm² wafer substrate, with around 60% of the wafer surface covered by aligned crystals. The quality of crystals can be easily controlled by tuning the dip-coating speed. Furthermore, OFETs based on well-aligned BPEA and TIPS-PEN single-crystalline nanoribbons were constructed. By optimizing channel lengths and using appropriate metallic electrodes, the BPEA and TIPS-PEN-based OFETs showed hole mobility exceeding 2.0 cm² V^-1 s^-1 (average mobility 1.2 cm² V^-1 s^-1) and 3.0 cm² V^-1 s^-1 (average mobility 2.0 cm² V^-1 s^-1), respectively. They both have a high on/off ratio (I _on/I _off) > 10⁹. The performance can well satisfy the requirements for light-emitting diodes driving.

Controllable domain morphology in coated poly(lactic acid) films for high-efficiency and high-precision transportation of water droplet arrays

Construction of superhydrophobic surfaces with tunable adhesion force has attracted considerable attention in past decades.