In Situ Characterization of the Triphase Contact Line in a Brush-Coating Process: Toward the Enhanced Efficiency of Polymer Solar Cells

Uniform Molecular Alignment on Ag-Doped Nickel Oxide Films

This study presents the uniform alignment of liquid crystal (LC) molecules on silver (Ag)-doped nickel oxide (NiO) films. The films were fabricated using a solution brush coating process, with Ag doping concentrations of 0, 10, and 20 wt%. X-ray photoelectron spectroscopy confirmed the successful formation of the films, while atomic force microscopy revealed nano/microgroove anisotropic structures, attributed to brush hair movement during coating. X-ray diffraction analysis indicated the films' amorphous nature. Optical transmittance measurements demonstrated their suitability for electronic display applications. Polarized optical microscopy verified uniform LC molecular alignment and effective optical control. The fabricated LC cells exhibited increased LC polar anchoring energy, improving device stability. The polar anchoring energy increased by 1159.02% after Ag doping. Additionally, reduced residual charge was observed, suggesting minimized image sticking. These findings indicate that Ag-doped NiO films are a promising alternative for LC alignment layers in functional LC systems.

Enhanced Electrical and Optical Properties of Bismuth Tantalum Oxide Thin Films through Graphene Oxide Doping

In this study, a hybrid thin film was fabricated by doping graphene oxide in a bismuth tantalum oxide solution in the sol-gel state. The thin film was produced by a brush-coating process. The graphene oxide doping ratios used were 0, 5, and 15 wt %. In the process of producing the thin film, the prepared sol-gel solution generates contraction forces, owing to the shear stress from the bristles of the brush, forming a microgroove structure. This structure was confirmed through atomic force microscopy, transmission electron microscopy, and energy-dispersive spectroscopy analyses. As a result of line profile analysis in atomic force microscopy, the groove heights of the thin film surface at 0, 5, and 15 wt % doping were 110, 130, and 160 nm, respectively, and the width of all grooves was 1 μm. The width of all thin films was approximately 1 μm, and microgrooves were confirmed. Moreover, the hybrid thin-film formation was confirmed by X-ray photoelectron spectroscopy. By comparing the electrical properties of the bismuth tantalum oxide thin film without graphene oxide doping and the thin film doped with 15 wt % graphene oxide, it was demonstrated that the electro-optical properties increased excellently with graphene oxide doping. Typically, the threshold voltage was reduced by approximately 0.26 V. Based on these observations, graphene oxide doped bismuth tantalum oxide hybrid thin films can be considered as promising candidates for thin-film applications in next-generation displays.

High electrical characteristics through graphene oxide doping process on physicochemically reformed inorganic thin films

This study investigated the improvement of the electro-optical properties of a liquid crystal (LC) cell fabricated through brush coating using graphene oxide (GO) doping. The physical deformation of the surface was analyzed using atomic force microscopy. The size of the groove increased as the GO dopant concentration increased, but the direction of the groove along the brush direction was maintained. X-ray photoelectron spectroscopy analysis confirmed that the number of C-C and O-Sn bonds increased as the GO concentration increased. Since the van der Waals force on the surface increases as the number of O-metal bonds increases, we were able to determine why the anchoring energy of the LC alignment layer increased. This was confirmed by residual DC voltage and anchoring energy measurements that were later performed. As the GO concentration increased, the width of the hysteresis curve decreased, indicating that the residual DC voltage decreased. Additionally, the 15% GO-doped sample exhibited a significant increase in its anchoring energy up to 1.34 × 10-3 J/m2, which is similar to that of rubbed polyimide. It also secured a high level of electro-optical properties and demonstrated potential as a next-generation thin-film display despite being produced via a simple brush-coating process.

Self-Aligned Liquid Crystals on Anisotropic Nano/Microstructured Lanthanum Yttrium Strontium Oxide Layer

We propose an efficient alignment method for liquid crystals (LCs). A brush-coating method handles film deposition and LC alignment treatment simultaneously herein, meaning a reduction in the conventional alignment layer treatment process steps. A lanthanum yttrium strontium oxide (LaYSrO) film prepared by the sol-gel process was used for the alignment layer. Topographical details of the brush-coated LaYSrO films (compared with spin-coated films) were investigated by atomic force microscopy. Spin-coated LaYSrO meant that the film formation alone without orientation treatment represented an isotropic surface. On the other hand, the 270 °C-cured brush-coated LaYSrO showed nano/microstructure with directionality. It indicates that brush-hair sweeping induced shearing stress on the sol state of the LaYSrO, which results in surface anisotropy for LC alignment. The uniform LC alignment state was confirmed by polarized optical microscopy and pretilt analysis. The brush-coated LaYSrO shows fine optical transparency compared to plain and indium-tin-oxide coated glasses, and thermal stability up to 150 °C for LC alignment. Competitive electro-optical performances of the brush-coated LaYSrO were verified in a twisted-nematic LC system compared to those of the conventionally used polyimide layer. Consequently, we expect that the brush-coating process can be an innovative technology for LC alignment.

Physicochemically Constructed Unidirectional Aluminum Bismuth Gallium Zinc Oxide Film for Enhanced Nematic Liquid Crystal System Using a Brush-Coating Method

We proposed a convenient brush coating method for liquid crystal (LC) alignment. This method conducted film deposition and alignment layer treatment process simultaneously. Aluminum bismuth gallium zinc oxide (AlBiGaZnO) was used as an alignment layer. After the curing process, a unidirectional AlBiGaZnO film was formed and the surface morphology and chemical composition was verified using scanning electron microscopy and X-ray photoelectron spectroscopy. This oriented structure of the surface was produced by shear-stress which originated from brush movement. That structure induced a surface anisotropic characteristic and resulted in a uniform LC alignment. The uniform and homogeneous LC alignment state on the film was confirmed using polarized optical microscopy and pre-tilt angle analysis. The brush coated AlBiGaZnO film exhibited excellent thermal budget for advanced LC system. The film exhibited enhanced electro-optical performance with a low operating voltage. These results demonstrate the potential of LC alignment technology via the brush coating method.

Meniscus-Assisted Coating with Optimized Active-Layer Morphology toward Highly Efficient All-Polymer Solar Cells

Morphology control is the key to engineering highly efficient solution-processed solar cells. Focusing on the most promising application-oriented photovoltaic all-polymer solar cells (all-PSCs), herein a facile and effective meniscus-assisted-coating (MAC) strategy is reported for preparing high-quality blend films with enhanced crystallinity and an interpenetrating nanofiber network morphology. The all-PSCs based on MAC exhibit excellent optoelectronic properties with efficiencies exceeding 15%, which is the best performance of solution-printing-based all-PSCs, as well as better stability. The crystallization kinetics of the polymer blend film is investigated by in situ UV-vis absorption spectroscopy, and the result explains the linear relationship between the meniscus advance speed and the crystallinity (crystallization rate) of the polymer. To verify the compatibility and universality of this strategy, the MAC strategy is applied to the other three binary systems. By precisely controlling the meniscus advancing speed, 1 cm² all-PSC devices whose efficiencies exceed 12% are fabricated. Such progress demonstrates that the application of the MAC strategy is a promising approach for the fabrication of high-efficiency all-PSCs.

Alignment of organic conjugated molecules for high-performance device applications

High-performance organic semiconductor materials as the electroactive components of optoelectronic devices have attracted much attention and made them ideal candidates for solution-processable, large-area, and low-cost flexible electronics. Especially, organic field-effect transistors (OFETs) based on conjugated semiconductor materials have experienced stunning progress in device performance. To make these materials economically viable, comprehensive knowledge of charge transport mechanisms is required. The alignment of organic conjugated molecules in the active layer is vital to charge transport properties of devices. The present review highlights the recent progress of processing-structure-transport correlations that allow the precise and uniform alignment of organic conjugated molecules over large areas for multiple electronic applications, including OFETs, organic thermoelectric devices (OTEs), and organic phototransistors (OPTs). Different strategies for regulating crystallinity and macroscopic orientation of conjugated molecules are introduced to correlate the molecular packing, the device performance and charge transport anisotropy in multiple organic electronic devices. This article is protected by copyright. All rights reserved.

A robust vertical nanoscaffold for recyclable, paintable, and flexible light-emitting devices

Organic light-emitting devices are key components for emerging opto- and nanoelectronics applications including health monitoring and smart displays. Here, we report a foldable inverted polymer light-emitting diode (iPLED) based on a self-suspended asymmetrical vertical nanoscaffold replacing the conventional sandwich-like structured LEDs. Our empty vertical-yet-open nanoscaffold exhibits excellent mechanical robustness, proven by unaltered leakage current when applying 1000 cycles of 40-kilopascal pressure loading/unloading, sonication, and folding, with the corresponding iPLEDs displaying a brightness as high as 2300 candela per square meter. By using photolithography and brush painting, arbitrary emitting patterns can be generated via a noninvasive and mask-free process with individual pixel resolution of 10 μm. Our vertical nanoscaffold iPLED can be supported on flexible polyimide foils and be recycled multiple times by washing and refilling with a different conjugated polymer capable of emitting light of different color. This technology combines the traits required for the next generation of high-resolution flexible displays and multifunctional optoelectronics.

Direct Writing Large-Area Multi-Layer Ultrasmooth Films by an All-Solution Process: Toward High-Performance QLEDs

With increasing the film area/layer, deteriorating in both smoothness and uniformity of thin-films frequently happen, which remains a barrier for making large-area quantum dot light-emitting diodes (QLEDs) by solution processes. Here, we demonstrated a facile all-solution process guided by the conical fiber array to write multi-layer ultrasmooth thin-films directly in centimeter scale. The side-by-side fibrous array helps to align surface tensions at the tri-phase contact line to facilitate large-area homogeneous deposition, which was verified by theoretical simulation. The Laplace pressure along individual conical fiber contributes to the steady liquid transfer. Thin-films with small roughness (<2.03 nm) and large-area (2×2 cm² ) uniformity were prepared sequentially on the target substrate, leading to large-area high-performance QLEDs. The result offers new insights for fabricating large-area high-performance thin-film devices.

Shear Induced TiO2 Nano Structure Using Brush-Coating for Liquid Crystal Alignment

We have developed a very useful and cost-effective liquid crystal (LC) alignment layer of brush-coated TiO2 that is solution-processable for twisted nematic (TN) LC cells. TiO2 was prepared via the sol-gel method. The TiO2 solution was brush-coated on the substrate, followed by an annealing process. During the brush-coating process, a retracting force is generated on the deposited TiO solutions along the coating direction. The annealing process hardens the TiO2 and generates shearing stress arising from the retracting force along the brush-coating direction. The shearing stress created highly oriented nano/microstructure and uniformly aligned LCs with a stable pretilt angle of 0.6°. TN mode LC cells based on brush-coated TiO2 exhibited a performance of 12.5 ms of response and a threshold voltage of 1.8 V. Our brush-coated TiO2 incorporates two steps of the film deposition and alignment process into one step.

Pen drawing display

As advancements in science and technology, such as the Internet of things, smart home systems, and automobile displays, become increasingly embedded in daily life, there is a growing demand for displays with customized sizes and shapes. This study proposes a pen drawing display technology that can realize a boardless display in any form based on the user's preferences, without the usual restrictions of conventional frame manufacturing techniques. An advantage of the pen drawing method is that the entire complex fabrication process for the display is encapsulated in a pen. The display components, light-emitting layers, and electrodes are formed using felt-tip drawing pens that contain the required solutions and light-emitting materials. The morphology and thickness of each layer is manipulated by adjusting the drawing speed, number of drawing cycles, and substrate temperature. This study is expected to usher in the upcoming era of customized displays that can reflect individual user needs.

Molecularly Aligned Hexa- peri-hexabenzocoronene Films by Brush-Coating and Their Application in Thin-Film Transistors

The facile Chinese brush-coating method was used to prepare oriented thin films of hexa- peri-hexabenzocoronene (HBC) derivatives on the silicon substrate. As a result of the directional solution-coating, the D_{3 h}-symmetry (HBC-1,3,5-Ph-C12) and the C₁-symmetry (HBC-1,2,4-Ph-C12) derivatives displayed an anisotropic alignment, with mostly edge-on orientation on SiO₂ surfaces modified with various silane-based monolayers. On these silane-modified surfaces, the higher symmetry molecule HBC-1,3,5-Ph-C12 developed a hexagonally packed superstructure, which provided greater π orbital overlap and presumably the electronic coupling between neighboring molecules. In particular, the use of an octyltrichlorosilane (OTS)-modified surface enabled brush-coated thin films to have higher anisotropic orientation, crystallinity, and favorable molecular arrangement. In contrast, the growth of the hexagonal packing of low-symmetry derivative HBC-1,2,4-Ph-C12 was only achieved on the phenyltrichlorosilane and OTS surfaces. Thin-film transistors based on these brush-coated films gave a maximum mobility of 0.1 and 0.056 cm² V^-1 s^-1, which are 2 orders of magnitude improvement over the devices with unoriented films prepared by spin-coating. The results indicate that the molecular packing of discotic liquid crystals on the silane-modified surface is sensitively influenced by the molecular symmetry, which affects intermolecular interactions as well as molecule/surface interactions. This study provides a simple way to fabricate aligned films for HBC derivatives for transistor application.