Selective Spin Dewetting for Perovskite Solar Modules Fabricated on Engineered Au/ITO Substrates.

We introduce a novel method for fabricating perovskite solar modules using selective spin-coating on various Au/ITO patterned substrates. These patterns were engineered for two purposes: (1) to enhance selectivity of monolayers primarily self-assembling on the Au electrode, and (2) to enable seamless interconnection between cells through direct contact of the top electrode and the hydrophobic Au connection electrode. Utilizing SAMs-treated Au/ITO, we achieved sequential selective deposition of the electron transport layer (ETL) and the perovskite layer on the hydrophilic amino-terminated ITO, while the hole transport layer (HTL) was deposited on the hydrophobic CH3-terminated Au connection electrodes. Importantly, our approach had a negligible impact on the series resistance of the solar cells, as evidenced by the measured specific contact resistivity of the multilayers. A significant outcome was the production of a six-cell series-connected solar module with a notable average PCE of 8.32%, providing a viable alternative to the conventional laser scribing technique.

Assessing the Role of Yarn Placement in Plated Knit Strain Sensors: A Detailed Study of Their Electromechanical Properties and Applicability in Bending Cycle Monitoring.

In this study, we explore how the strategic positioning of conductive yarns influences the performance of plated knit strain sensors fabricated using commercial knitting machines with both conductive and non-conductive yarns. Our study reveals that sensors with conductive yarns located at the rear, referred to as 'purl plated sensors', exhibit superior performance in comparison to those with conductive yarns at the front, or 'knit plated sensors'. Specifically, purl plated sensors demonstrate a higher sensitivity, evidenced by a gauge factor ranging from 3 to 18, and a minimized strain delay, indicated by a 1% strain in their electromechanical response. To elucidate the mechanisms behind these observations, we developed an equivalent circuit model. This model examines the role of contact resistance within varying yarn configurations on the sensors' sensitivity, highlighting the critical influence of contact resistance in conductive yarns subjected to wale-wise stretching on sensor responsiveness. Furthermore, our findings illustrate that the purl plated sensors benefit from the vertical movement of non-conductive yarns, which promotes enhanced contact between adjacent conductive yarns, thereby improving both the stability and sensitivity of the sensors. The practicality of these sensors is confirmed through bending cycle tests with an in situ monitoring system, showcasing the purl plated sensors' exceptional reproducibility, with a standard deviation of 0.015 across 1000 cycles, and their superior sensitivity, making them ideal for wearable devices designed for real-time joint movement monitoring. This research highlights the critical importance of conductive yarn placement in sensor efficacy, providing valuable guidance for crafting advanced textile-based strain sensors.

Combined Ultraviolet Ozone and Thermally Activated Formamidinium Iodide Solution to Fabricate Large Grain FAPbI2.6Br0.3Cl0.1 Films.

In this report, we report the fabrication of a large grain and high crystallinity perovskite film by combined ultraviolet-ozone (UVO) and thermal treatment of formamidinium iodide solution during the fabrication of formamidinium lead halide (FAPbI2.6Br0.3Cl0.1) films by a two-step deposition method. In this process, lead halide films were treated with UVO-treated FAI at different times. In addition, we have observed that hot-casting of UVO-assisted FAI nucleates the α-FAPbI3 phase in as-prepared films. Again, we observed that the annealed hot-cast UVO-assisted FAI increased the grain size and crystallinity in the films. It was observed that the perovskite film fabricated using 10 min UVO-treated FAI solution shows the highest power conversion efficiency (PCE) up to 17.74%. Furthermore, the perovskite film fabricated with the hot-cast at 120 °C with the 10 min UVO-treated FAI solution improved the PCE to 19.22%. This finding would help with fabrication of large grain, smooth, uniform, and pinhole perovskite films by combining UVO and thermally assisted FAI solution.

Effects of the PbBr2:PbI2 Molar Ratio on the Formation of Lead Halide Thin Films, and the Ratio's Application for High Performance and Wide Bandgap Solar Cells.

We investigate the effects of the molar ratio (x) of PbBr2 on the phases, microstructure, surface morphology, optical properties, and structural defects of mixed lead halides PbI2(1-x)Br2x for use in solar cell devices. Results indicate that as x increased to 0.3, the surface morphology continued to improve, accompanied by the growth of PbI2 grains. This resulted in lead halide films with a very smooth and continuous morphology, including large grains when the film was formed at x = 0.3. In addition, the microstructure changed from (001)-oriented pure PbI2 to a highly (001)-oriented ß (PbI2-rich) phase. The plausible mechanism for the enhanced morphology of the lead halide films by the addition of PbBr2 is proposed based on the growth of a Br-saturated lead iodide solid solution. Furthermore, iodine vacancies, identified by X-ray photoelectron spectroscopy, decreased as the ratio of PbBr2 increased. Finally, an electrical analysis of the solar cells was performed by using a PN heterojunction model, revealing that structural defects, such as iodine vacancies and grain boundaries, are the main contributors to the degradation of the performance of pure PbI2-based solar cells (including high leakage, low stability, and high hysteresis), which was significantly improved by the addition of PbBr2. The solar cell fabricated at x = 0.3 in air showed excellent stability and performance. The device lost merely 20% of the initial efficiency of 4.11% after 1500 h without encapsulation. This may be due to the dense microstructure and the reduced structural defects of lead halides formed at x = 0.3.

Fibertronic Organic Light-Emitting Diodes toward Fully Addressable, Environmentally Robust, Wearable Displays.

Significant potential of electronic textiles for wearable applications has triggered active studies of luminescent fibers toward smart textile displays. In spite of notable breakthroughs in the lighting fiber technology, a class of information displays with a luminescent fiber network is still underdeveloped due to several formidable challenges such as limited electroluminescence fiber performance, acute vulnerability to chemical and mechanical factors, and lack of decent engineering schemes to form fibers with robust interconnectable pixels for two-dimensional matrix addressing. Here, we present a highly feasible strategy for organic light-emitting diode (OLED) fiber-based textile displays that can overcome these issues by implementing prominent solution options including compatible fabrication method of OLED pixel arrays on adapted fiber configurations and chemically/mechanically sturdy but electrically conductive passivation system. To create solid interconnectable OLED fibers without compromising the high electroluminescence performance, phosphorescence OLED materials are deposited onto process-friendly fibers of rectangular stripes, where periodically patterned OLED pixels are selectively passivated with robust polymer and circumventing metal pads by a stamp-assisted printing method. A woven textile of interlaced interconnectable OLED fibers with perpendicularly arranged conductive fibers serves as a matrix-addressable two-dimensional network that can be operated by the passive matrix scheme. Successful demonstrations of stably working woven OLED textile in the water, as well as under the applied tensile force, support feasibility of the present approach to reify fully addressable, environmentally durable, fiber-based textile displays.

Plasmonically Engineered Textile Polymer Solar Cells for High-Performance, Wearable Photovoltaics.

A practically applicable type of wearable polymer solar cells (PSCs) is presented with the enhanced performance by exploiting simply embodied, plasmonic nanostructures on a commercially available textile platform of optically opaque, geometrically uneven, and physically permeable woven fabrics that are commonly not compatible with organic photovoltaics. On a conformable fabric substrate preferentially processed with organic/inorganic multilayers for both planarization and encapsulation, the fabrication of top-illuminated, inverted type of PSCs with a transparent top electrode consisting of optimized dielectric/metal/dielectric multilayers is conducted, where a nanostructure of disorderly distributed elliptical hemispheres is implanted at an opaque bottom silver electrode by spin-coated silica nanoparticles in advance of depositing this electrode. The nanostructured bottom electrode promotes the light trapping effect at wavelengths of the surface plasmon resonance, as well as reduces the electrical Ohmic loss, thereby achieving a device with the power conversion efficiency of ∼8.71% at the given plasmonic device, where a net improvement of the efficiency is ∼1.46% compared to the planar device comprising otherwise same constituent layers. Systematic studies on optical properties and associated photovoltaic performance in experiments, together with analytic numerical modeling, allow quantitative understanding of the underlying physics, providing optimal rules for tailoring random nanostructures to the textile PSCs in the context of high-performance wearable photovoltaics.

Indium tin oxide-free PEDOT:PSS/SAM/MoO3/Au/MoO3 multilayer electrodes for organic solar cells.

A MoO3/Au/MoO3 (MAM) tri-layer structure was developed as a transparent, low-resistance anode for use in organic solar cells. Transmittance was maximized at 82% using symmetric bottom and top MoO3 layers (each of thickness 30 nm) either side of a 12 nm Au layer. Low sheet resistance also resulted (7.4 ohm per square). The series resistance and optical transmission of devices employing these structures as anodes were tailored by varying the thickness of the top MoO3 layer. Dissolution of the top MoO3 layer in PEDOT: PSS degraded the cells, which could be decreased by the deposition of a self-assembled monolayer of 16-phosphonohexadecanoic acid on the MoO, prior to spin-coating the PEDOT: PSS. Cells fabricated on PEDOT: PSS/SAMs/MAM multilayer electrodes showed a power conversion efficiency of 2.33%, comparable to that of ITO-based organic solar cells. The PEDOT: PSS/SAMs/MAM electrode was shown to be a promising replacement of ITO for use in low-cost optoelectronic devices.

Memory effect of low-temperature processed ZnO thin-film transistors having metallic nanoparticles as charge trapping elements.

In this study, non-volatile memory effect was characterized using the single-transistor-based memory devices based on self-assembled gold nanoparticles (AuNP) as the charge trapping elements and atomic-layer deposited ZnO as the channel layer. The fabricated memory devices showed controllable and reliable threshold voltage shifts according to the program/erase operations that resulted from the charging/discharging of charge carriers in the charge trapping elements. Reliable non-volatile memory properties were also confirmed by the endurance and data retention measurements. The low temperature processes of the key device elements, i.e., AuNP charge trapping layer and ZnO channel layer, enable the use of this device structure to the transparent/flexible non-volatile memory applications in the near future.

High performance flexible organic thin film transistors (OTFTs) with octadecyltrichlorsilane/ Al2O3/poly(4-vinylphenol) multilayer insulators.

The incorporation of a thin, atomic layer deposited Al2O3 layer in between a spin-coated poly-4-vinyl phenol (PVP) organic layer and octadecyltrichlorsilane (OTS) in the multilayer gate dielectric for pentacene organic thin film transistors on a n(+)-Si substrate reduced the gate leakage current and thereby significantly enhanced the current on/off ratio up to 2.8 x 10(6). Addition of the OTS monolayer on the UV-treated Al2O3 improved the crystallinity of the pentacene layer, where the OTS/UV-treated Al2O3 surfaces increased their contact angles to 100 degrees. X-ray diffraction (XRD) analysis revealed a more intense (001) crystal reflectance of pentacene deposited on OTS/UV-treated Al2O3 surface than that on OTS/Al2O3 surface. Moreover, the improved pentacene layer contributed to the field effect mobility (0.4 cm2/Vs) and subsequently improved the electrical performances of organic thin film transistor (OTFT) devices. This PVP/UV treated Al2O3/OTS multilayer gate dielectric stack was superior to those of the device with the single PVP gate dielectrics due to the improved crystallinity of pentacene.

A novel method for patterning of poly(3,4-ethylenedioxythiophene) films using UV exposure-activated self-assembled monolayers.

We have investigated a novel method for patterning of (3, 4-ethylenedioxythiophene) PEDOT, which has involved a selective polymerization of PEDOT on an UV-activated Self-Assembled-Monolayer surface. OTS coated surface has been activated by UV exposure, and the UV-exposed area served as adsorption sites for FeCl3 oxidants, providing a selective deposition of PEDOT films on FeCl3 adsorbed area, and thus leading to the selective patterning of PEDOT films. UV irradiation time and mask pattern dimension are main contributors to patternability: UV irradiation through Cr-mask (3 microm design) lead to approximately 3-5 microm patterns of PEDOT films, depending on the UV exposure time. In addition, a scotch tape peel test revealed excellent adhesion property of PEDOT to SiO2. Consequently, this simple method can be applied to define deep submicron dimensions due to its ability of providing a direct transfer of mask patterns to the substrate.

Fabrication of an a-IGZO thin film transistor using selective deposition of cobalt by the self-assembly monolayer (SAM) process.

Interest in transparent oxide thin film transistors utilizing ZnO material has been on the rise for many years. Recently, however, IGZO has begun to draw more attention due to its higher stability and superior electric field mobility when compared to ZnO. In this work, we address an improved method for patterning an a-IGZO film using the SAM process, which employs a cost-efficient micro-contact printing method instead of the conventional lithography process. After a-IGZO film deposition on the surface of a SiO2-layered Si wafer, the wafer was illuminated with UV light; sources and drains were then patterned using n-octadecyltrichlorosilane (OTS) molecules by a printing method. Due to the low surface energy of OTS, cobalt was selectively deposited on the OTS-free a-IGZO surface. The selective deposition of cobalt electrodes was successful, as confirmed by an optical microscope. The a-IZGO TFT fabricated using the SAM process exhibited good transistor performance: electric field mobility (micro(FE)), threshold voltage (V(th)), subthreshold slope (SS) and on/off ratio were 2.1 cm2/Vs, 2.4 V, 0.35 V/dec and 2.9 x 10(6), respectively.

Temperature dependence of bis(triisopropylsilylethynyl)-pentacene nanofilm deposited on octadecyltrichlorosilane self assembled monolayer surface as a transistor channel.

Highly pure 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN) nanofilms were deposited on a hydrophobic OTS-SAM surface at two different substrate temperatures (70 degrees C and 90 degrees C) via the vacuum thermal evaporation (VTE) method. X-ray reflectivity measurements over a wide temperature range (30 degrees C-284 degrees C) revealed that out-of-plane crystallinity of the film (approximately 10 nm) remains intact but in-plane crystallinity starts to become poor from approximately 100 degrees C, and to become much more worse from 260 degrees C. Atomic force microscope images showed that TIPS-PEN films (approximately 55 nm) prepared at the substrate temperature of 90 degrees C or above commonly have a number of huge cracks between enormous crystal domains (up to 3 microm) whereas the films didn't form such morphology below T(s) = 90 degrees C. These results clearly suggest that an optimum substrate temperature of TIPS-PEN nanofilms on OTS-SAM surface must be somewhere between 70 degrees C and 90 degrees C, and the process temperature must be kept below 90 degrees C in order to form and maintain a highly crystalline film for an organic thin film transistor device since in-plane crystallinity of a semiconductor channel deeply affects the performance of a transistor.

Highly efficient phosphor-converted white organic light-emitting diodes with moderate microcavity and light-recycling filters.

We demonstrate the combined effects of a microcavity structure and light-recycling filters (LRFs) on the forward electrical efficiency of phosphor-converted white organic light-emitting diodes (pc-WOLEDs). The introduction of a single pair of low- and high-index layers (SiO(2)/TiO(2)) improves the blue emission from blue OLED and the insertion of blue-passing and yellow-reflecting LRFs enhances the forward yellow emission from the YAG:Ce(3+) phosphors layers. The enhancement of the luminous efficacy of the forward white emission is 1.92 times that of a conventional pc-WOLED with color coordinates of (0.34, 0.34) and a correlated color temperature of about 4800 K.

Mobility enhanced photoactivity in sol-gel grown epitaxial anatase TiO2 films.

Epitaxial anatase thin films were grown on single-crystal LaAlO3 substrates by a sol-gel process. The epitaxial relationship between TiO2 and LaAlO3 was found to be [100]TiO2||[100]LaAlO3 and (001)TiO2||(001)LaAlO3 based on X-ray diffraction and a high-resolution transmission electron microscopy. The epitaxial anatase films show significantly improved photocatalytic properties, compared with polycrystalline anatase film on fused silica substrate. The increase in the photocatalytic activity of epitaxial anatase films is explained by enhanced charge carrier mobility, which is traced to the decreased grain boundary density in the epitaxial anatase film.

Controllable feature sizes of highly conductive poly(3,4-ethylenedioxythiophene) nanofilms patterned on SiO2 surface.

In this paper, we report a novel patterning method for a poly(3,4-ethylenedioxythiophene) (PEDOT) nanofilm deposited on an OTS monolayer-coated silicon wafer substrate by the vapor phase polymerization method. To scrutinize the adhesion improvement, electrical conductivity and feature controllability, patterned PEDOT nanofilms were investigated with a Scotch tape peel test, I-V curve measurement, and optical and atomic force microscopes. The scrutinization strongly indicates that the adhesion improvement is most likely due to direct chemical bonds formed between ethylenedioxythiophene (EDOT) molecules and photo-oxidized OTS monolayer during a vapor phase polymerization reaction. The investigation also discovered that the feature size of the film can be chemically controlled by the reaction between OTS and reactive atomic oxygen gases, and the patterned films generally show a noticeably good electrical conductivity (approximately 500 S/cm at merely approximately 100 nm thick film). These results successfully demonstrate that the patterned PEDOT nanofilms are qualified enough to be employed as an electrode component of an OTFT device since the electrode materials must show an electrical conductivity of at least 50 S/cm or higher.

Significantly improved adhesion of poly(3,4-ethylenedioxythiophene) nanofilms to amino-silane monolayer pre-patterned SiO2 surfaces.

This study reports a novel patterning method for highly pure poly(3,4-ethylenedioxythiophene) (PEDOT) nanofilms having a particularly strong adhesion to a SiO2 surface. An oxidized silicon wafer substrate was micro-contact printed with n-octadecyltrichlorosilane (OTS) monolayer, and subsequently its negative pattern was self-assembled with three different amino-functionalized alkylsilanes, (3-aminopropyl)trimethoxysilane (APS), N-(2-aminoethyl)-3-aminopropyltrimethoxy silane (EDAS), and (3-trimethoxysilylpropyl) diethylenetriamine (DETS). Then, PEDOT nanofilms were selectively grown on the aminosilane pre-patterned areas via the vapor phase polymerization method. To evaluate the adhesion and patterning, the PEDOT nanofilms and SAMs were investigated with a Scotch tape test, contact angle analyzer, optical and atomic force microscopes. The evaluation revealed that the newly developed bottom-up process can successfully offer a strongly adhered and selectively patterned PEDOT nanofilm on an oxidized Si wafer surface.

Layer-by-layer assembled charge-trap memory devices with adjustable electronic properties.

We describe a versatile approach for preparing flash memory devices composed of polyelectrolyte/gold nanoparticle multilayer films. Anionic gold nanoparticles were used as the charge storage elements, and poly(allylamine)/poly(styrenesulfonate) multilayers deposited onto hafnium oxide (HfO2)-coated silicon substrates formed the insulating layers. The top contact was formed by depositing HfO2 and platinum. In this study, we investigated the effect of increasing the number of polyelectrolyte and gold nanoparticle layers on memory performance, including the size of the memory window (the critical voltage difference between the 'programmed' and 'erased' states of the devices) and programming speed. We observed a maximum memory window of about 1.8 V, with a stored electron density of 4.2 x 1012 cm-2 in the gold nanoparticle layers, when the devices consist of three polyelectrolyte/gold nanoparticle layers. The reported approach offers new opportunities to prepare nanostructured polyelectrolyte/gold nanoparticle-based memory devices with tailored performance.

Emergence of vanA Genotype Vancomycin-Resistant Enterococci with Low or Moderate Levels of Teicoplanin Resistance in Korea.

In Korea, vancomycin-resistant enterococci have become important nosocomial pathogens since the late 1990s, and most vancomycin-resistant enterococcal isolates have been VanA phenotype-vanA genotype strains. In 2001, we experienced an outbreak of VanB phenotype-vanA genotype vancomycin-resistant enterococci at a university hospital. This is the first report of VanB-vanA vancomycin-resistant enterococci from humans in Korea.