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Since the first demonstration of perovskite solar cells (PSCs) was reported, there have been many efforts to improve the stability by investigating the degradation mechanism. This is because PSCs are considerably vulnerable to the moisture in air. In this letter, we demonstrate highly stable and robust PSCs employing the stack structure by solution-processed fluorocarbon films as a passivation layer, Teflon-AF which exhibits high hydrophobicity for efficient removal of water molecules. Material characterization using x-ray diffraction proves that the improved stability of PSCs under harsh humidity (70%) results from the effective and practical passivation that suppresses the chemical interaction of perovskite films with water molecules. It must be noted that the proposed passivation can be realized by simple spin-coating methods at low temperature of 70 °C, which can open up a promising route to raise the technological interest in the process cost and temperature.

The material compositions of oxide films have been extensively investigated in an effort to improve the electrical characteristics of dielectrics which have been utilized in various electronic devices such as field-effect transistors, and storage capacitors. Significantly, solution-based compositions have attracted considerable attention as a highly effective and practical technique to replace vacuum-based process in large-area. Here, we demonstrate solution-processed composite films consisting of aluminum oxide (Al2O3) and boron nitride (BN), which exhibit remarkable dielectric properties through the optimization process. The leakage current of the optimized Al2O3–BN thin films was decreased by a factor of 100 at 3V, compared to pristine Al2O3 thin film without a loss of the dielectric constant or degradation of the morphological roughness. The characterization by X-ray photoelectron spectroscopy measurements revealed that the incorporation of BN with an optimized concentration into the Al2O3 dielectric film reduced the density of oxygen vacancies which act as defect states, thereby improving the dielectric characteristics.

In this work, we propose a new mixed halide precursor composition for MAPbI 3-x Cl x organic/inorganic perovskite (PRV) solar cells. PRV films made with a new precursor composition of (MAI: PbCl 2 : PbI 2 = 2 : 1 : 1) could be crystallized at lower temperature (70 °C) and shorter annealing duration (60 min), whereas previous standard composition (MAI: PbCl 2 = 3 : 1) requires multi-step and high temperature (from 75 °C to 130 °C) annealing for longer durations (∼100 min). By adopting the suggested composition, much uniform surface morphology of PRV light harvester was obtained even though non-polar solvent washing was not introduced yet. Also, when the suitable toluene washing treatment was introduced, PRV surfaces of highly compact and large crystallites with regular distribution were achieved without any pinhole, which offered significant improvements in fill factor (41 → 65%) and power conversion efficiency (5.85 → 9.39%) of PRV cells. The suggested new precursor composition contributing for surface topography can be widely utilized for inverted planar PRV devices with low-temperature and simple processing.

We demonstrate a practical and robust encapsulation for environment-stable solar window modules based on multi-crystalline silicon solar cells with ultra-violet-curable optically clear resin (OCR) films. Compared to encapsulation with polyvinyl butyral (PVB) films, OCR films significantly improved the operational stability in solar window modules following a harsh damp heat test, at 85 °C of temperature and 85% of relative humidity for 1 k h. Such advance can be realized by suppressed chemical reactions with water molecules in OCR films. We further investigate the optical characteristics of PVB and OCR encapsulation films using ultraviolet/vis. spectrophotometer and Fourier-transform infrared spectroscopy measurements to support the claim. We believe that this is the first module-level demonstration (400 mm × 400 mm) of solar windows encapsulated with OCR films fabricated below 60 °C by using UV curing technology, which exhibit a power conversion efficiency of ∼10%, even after undergoing the damp heat tests.

Wearable triboelectric nanogenerators (TENGs) are considered viable for mobile applications of self-powered electronics operating on human body but limited by relatively low output performance. In this study, the effects of interfacial layers used as hole transport layers (HTLs) which affect triboelectric charge separation on the output performance of TENGs are investigated. Comparative analyses of different interfacial layers prove that the incorporation of single-wall carbon nanotube (SWCNT) random networks into TENGs can reduce the loss of triboelectric charges. Improvements in the charge-repelling force and hole-blocking barrier at the interface between the HTL and electrode enabled the wearable TENGs to achieve output voltages of ∼760 V and currents of ∼51 μA at 3 Hz. Such advances can be realized by optimizing SWCNT-based HTL through a simple and effective bar-printing technology in an ambient atmosphere. Moreover, a practical application of the wearable TENG exhibiting a maximum instantaneous power of 19.2 mW and a power density of 0.77 mWcm−2 with a load resistance of 5 MΩ is demonstrated. Mechanical finger-tapping on wearable TENGs enables operation of small electric devices without energy storage. The utilization of SWCNT-based HTLs fabricated by effective and practical bar-printing can stimulate the development of energy-harvesting technologies based on wearable TENGs.

Although conventional skin-attachable electronics exhibit good functionalities, their direct attachment (without any adhesive) to human skin with sufficient conformal contact is challenging. Herein, all-solution-processed on-skin electronics based on self-reconfigurable high-weight-per- volume-gelatin (HWVG) film constructed using an effective, biocompatible water absorption-evaporation technique are demonstrated. Completely conformal contact of self-reconfigurable HWVG films is realized by rapidly inducing anisotropic swelling in the perpendicular direction and covering any curvature on the skin without spatial gap or void after shrinking. A sufficiently thin HWVG film (~2 um) exhibited higher adhesion owing to van der Waals force and the carboxylic acid and amine groups in HWVG film form cross-linkages through intermolecular bonds with human skin. Self-reconfigurable HWVG films with high biocompatibility are optimized to afford a superior efficiency of 87.83 % at a concentration of 20 % (w/v) and a storage modulus of 1822 MPa at 36.5 °C. Furthermore, functional nanoelectrodes consisting of self-reconfigurable silver nanowires/HWVG films for high-performance on-skin sensors allowing the detection of sensitive motion and electrophysiological signals, as well as an armband-type sensor system incorporated with a smartphone for health-care monitoring are demonstrated. Outstanding performances, including stability, reliability, flexibility, re-usability, biocompatibility, and permeability of on-skin electronics based on HWVG films can open-up a prospective route to realizing breathable human-machine interfaces based on biocompatible materials and processes.

In this study, we demonstrate the characteristics of high quality boron nitride (BN) thin films for high performance 2 dimensional nanoelectronics. Such thin films were deposited using solution-pro ...

In this paper, we investigated the strontium doping effects on the electrical and physical characteristics of solution-processed aluminum oxide dielectric layer and its application to low-voltage-operated indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs). With an optimized doping concentration of strontium (5 at%) in aluminum oxide (Al 2 O 3 ), an oxide gate dielectric layer having a dielectric constant of ~7 and low leakage current characteristics (~4 × 10 −7 A/cm 2 at 3 MV/cm) could be achieved by a solution process, which are comparably better than those of pristine Al 2 O 3 film. The enhanced dielectric properties from strontium doping can be attributed to the change in the physical properties of Al 2 O 3 film incorporated with strontium, providing charge relaxation of defect states in Al 2 O 3 film. Also, since the strontium is highly reactive with oxygen, the strontium substitution through a doping leads to more strongly bound structure in an Al 2 O 3 film without considerable lattice distortion. Using the strontium-doped aluminum oxide film as a gate dielectric layer, having a thickness less than 10 nm, solution-processed IGZO TFTs operating at ≤ 1 V were demonstrated showing a field-effect mobility of 1.74 ± 1.10 cm 2 /V s and an on-current level of ~10 −5 A.

Given that power consumption and short-channel effects exist in a trade-off relationship, there has been much effort to investigate short-channel transistors which enable relative reductions in the operating voltage. Recently, the feasibility of transistors operating at ultra-low voltages with a nanometer-scale channel length has been extensively investigated for future nanoelectronics. Here, we demonstrate solution-processed single-walled carbon nanotubes-based thin-film transistors (SWCNT-TFTs) with a sub-20-nm-channel operating at ultra-low voltages which utilize an electromigration technique that induces a broken bridge of nanoparticles. By employing the post-treatment process of thermal annealing in a vacuum, the charge transport of the short-channel SWCNT-TFTs was improved. The origin of such improvements is presumed to reduce the charge impurities, including organic/inorganic residues as defect states, as well as to improve electric contact between the SWCNT and the metal electrode, which strongly affects the one-dimensional charge transport.

In this article, we demonstrate the potential of solution-processed boron nitride (BN) thin films for high performance single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) with low-voltage operation. The use of BN thin films between solution-processed high-k dielectric layers improved the interfacial characteristics of metal-insulator-metal devices, thereby reducing the current density by three orders of magnitude. We also investigated the origin of improved device performance in SWCNT-TFTs by employing solution-processed BN thin films as an encapsulation layer. The BN encapsulation layer improves the electrical characteristics of SWCNT-TFTs, which includes the device key metrics of linear field-effect mobility, sub-threshold swing, and threshold voltage as well as the long-term stability against the aging effect in air. Such improvements can be achieved by reduced interaction of interfacial localized states with charge carriers. We believe that this work can open up a promising route to demonstrate the potential of solution-processed BN thin films on nanoelectronics.

We demonstrate all-solution-processed pressure sensors consisting of carbon-based nano-composites with a wavy configuration using patterned polydimethylsiloxane molds. The sensitivity of the proposed sensors was increased by 36% at the applied pressure levels of 1 k N/ $\text{m}^{2}$ . Significantly, the resistance was mostly recovered after a release from 3 M N/ $\text{m}^{2}$ without conspicuous hysteresis, and a very stable and robust operation was secured during the pressure and release cycle. Compared with the as-supplied pressure-sensitive rubber films, the carbon-based nano-composite with a wavy configuration exhibited gradual changes, including a linear change in the low-pressure regime.

Ultrasensitive room-temperature operable gas sensors utilizing the photocatalytic activity of Na-doped p-type ZnO (Na:ZnO) nanoflowers (NFs) are demonstrated as a promising candidate for diabetes detection. The flowerlike Na:ZnO nanoparticles possessing ultrathin hierarchical nanosheets were synthesized by a facile solution route at a low processing temperature of 40 °C. It was found that the Na element acting as a p-type dopant was successfully incorporated in the ZnO lattice. On the basis of the synthesized p-type Na:ZnO NFs, room-temperature operable chemiresistive-type gas sensors were realized, activated by ultraviolet (UV) illumination. The Na:ZnO NF gas sensors exhibited high gas response (S of 3.35) and fast response time (∼18 s) and recovery time (∼63 s) to acetone gas (100 ppm, UV intensity of 5 mW cm–2), and furthermore, subppm level (0.2 ppm) detection was achieved at room temperature, which enables the diagnosis of various diseases including diabetes from exhaled breath.

High performance of solution-processed, single-wall-carbon-nanotube (SWCNT) thin-film transistors (TFTs) is investigated through the use in the different gatedielectrics of silicon dioxide (SiO2), silicon nitride (SiNx), the bilayers of SiO2 and SiNx, and hexagonal boron-nitride (h-BN) thin films. The different interfacial characteristics affect the electrical characteristics of the SWCNT-TFTs including key device metrics. Significantly, the hysteresis window that is normally observed in drop-casted SWCNT-TFTs was majorly suppressed by the employment of a thin lower dielectric-constant material on a higher dielectricconstant material. Sub-2V operating SWCNT-TFTs with solution-processed h-BN gate dielectrics with good above- and sub-threshold characteristics are also investigated on the basis of interfacial characteristics underlying the device physics. Such performance can be realized by the suppressed interfacial impurity scattering through the chemically clean interface combined with optimized solution-process below 100 °C.

Introduction: Compression of the lateral femoral cutaneous nerve (LFCN), known as meralgia paresthetica (MP), is common. We investigated the topographic anatomy of the LFCN focusing on the inguinal ligament and adjacent structures. Methods: Distances from various bony and soft-tissue landmarks to the LFCN were investigated in 33 formalin-embalmed cadavers. Results: The mean distance from the anterior superior iliac spine (ASIS) to the LFCN was 8.8 mm. In approximately 90% of cases, the LFCN lay

The use of the charge-screening method to obtain high-performance solution-processed zinc–tin-oxide (ZTO) thin-film transistors (TFTs) for transparent flexible displays is investigated. The proposed ZTO TFTs employing solution-processed ferroelectric, poly (vinylidenefluoride-co- trifluoroethylene) (PVDF-TrFE) copolymer exhibit excellent switching characteristics, including a shift in the threshold voltage toward 0 V and a decrease in the OFF-state current and the sub-threshold swing. The long-term stability of ZTO/PVDF-TrFE TFTs against electrical bias combined with visible-light illumination at 60 °C is also demonstrated. The proposed method is based on an all-solution-process that was carried out below 100°C except the metal deposition, and this allows the ZTO TFT matrix to be integrated into transparent display backplanes on flexible substrates.

Cylindrical fullerenes (or carbon nanotubes (CNTs)) have been extensively investigated as potential sensor platforms due to effective and practical manipulation of their physical and chemical properties by functionalization/doping with chemical groups suitable for novel nanocarrier systems. CNTs play a significant role in biomedical applications due to rapid development of synthetic methods, structural integration, surface area-controlled heteroatom doping, and electrical conductivity. This review article comprehensively summarized recent trends in biomedical science and technologies utilizing a promising nanomaterial of CNTs in disease diagnosis and therapeutics, based on their biocompatibility and significance in drug delivery, implants, and bio imaging. Biocompatibility of CNTs is essential for designing effective and practical electronic applications in the biomedical field particularly due to their growing potential in the delivery of anticancer agents. Furthermore, functionalized CNTs have been shown to exhibit advanced electrochemical properties, responsible for functioning of numerous oxidase and dehydrogenase based amperometric biosensors. Finally, faster signal transduction by CNTs allows charge transfer between underlying electrode and redox centres of biomolecules (enzymes).

Amorphous metal-oxide semiconductors (AOSs) such as indium-gallium-zinc-oxide (IGZO) as an active channel have attracted substantial interests with regard to high-performance thin-film transistors (TFTs). Recently, intensive and extensive studies of flexible and/or wearable AOS-based TFTs fabricated by solution-process have been reported for emerging approaches based on device configuration and fabrication process. However, several challenges pertaining to practical and effective solution-process technologies remain to be resolved before low-power consuming AOS-based TFTs for wearable electronics can be realized. In this paper, we investigate the non-thermal annealing processes for sol-gel based metal-oxide semiconductor and dielectric films fabricated by deep ultraviolet (DUV) photo and microwave annealing at low temperature, compared to the conventional thermal annealing at high temperature. A comprehensive investigation including a comparative analysis of the effects of DUV photo and microwave annealing on the degree of metal-oxide-metal networks in amorphous IGZO and high-dielectric-constant (high-k) aluminum oxide (Al2O3) films and device performance of IGZO-TFTs in a comparison with conventional thermal annealing at 400 °C was conducted. We also demonstrate the feasibility of wearable IGZO-TFTs with Al2O3 dielectrics on solution-processed polyimide films exhibiting a high on/off current ratio of 5 × 104 and field effect mobility up to 1.5 cm2/V-s operating at 1 V. In order to reduce the health risk and power consumption during the operation of wearable electronics, the operating voltage of IGZO-TFTs fabricated by non-thermal annealing at low temperature was set below ~1 V. The mechanical stability of wearable IGZO-TFTs fabricated by an all-solution-process except metal electrodes, against cyclic bending tests with diverse radius of curvatures in real-time was investigated. Highly stable and robust flexible IGZO-TFTs without passivation films were achieved even under continuous flexing with a curvature radius of 12 mm.

The aim of this study was to identify the three-dimensional topography of the sphenoid door jamb (SDJ) in the lateral orbital wall and to propose navigational guidelines for safe deep lateral decompression using surgical landmarks. The 120 orbits and SDJs of 60 subjects were three-dimensionally reconstructed using Mimics software. The mean volumes of the orbit and SDJ were 24.3 mm3 and 2.0 mm3, respectively. The mean distances from the lateral orbital margin (LOM) to the anterior and posterior margins of the SDJ were 13.2 and 36.3 mm, respectively. The mean distances from the superior orbital fissure to the LOM and to the posterior margin of the SDJ were 40.2 mm and 4.6 mm, respectively. The mean distances from the inferior orbital fissure (IOF) to the anterior and posterior margins of the SDJ were 3.8 mm and 20.5 mm, respectively. In the superior approach of the orbit, it can be predicted that the area up to 3 cm posterior from the LOM is safe, while 1 cm posterior from the safe zone could be a dangerous zone. In the inferior approach of the orbit, the safe area will be about 1 cm posterior from the anterior tip of the IOF, and the area up to 1 cm posterior from the safe zone should be approached with extreme care.

High dielectric constant (high-k) materials have been extensively investigated for low-voltage operating electronics. In recent years, solution-processed high-k dielectrics have been of technological interests in low fabrication cost, large area process and good film quality, compared to the vacuum-process technology. In this paper, we demonstrate solution-processed aluminum oxide (Al2O3) dielectrics for high performance solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs) operating at low voltage. The material and electrical properties of Al2O3 dielectrics fabricated at different post-annealing temperatures were analyzed by atomic force microscopy, scanning electron microscopy, X-ray diffraction and capacitance-voltage measurements. We also investigate the effect of crystalline Al2O3 dielectrics on the device performance of solution-processed IGZO TFTs. It is concluded that improved interfacial characteristics of crystalline Al2O3 dielectrics enhance the device performance of solution-processed IGZO TFTs operating at 3 V.

Polymer FETs generally have a wide subthreshold regime due to a lot of disorder, mainly originated from domain/grain boundaries. Deep state’s charge transport of polymer transistors has not been investigated due to the difficulty in determining the field-effect mobility in the subthreshold region. In this paper, the features of the charge transport in deep and shallow states of polymer transistors will be discussed in detail through an accurate modeling and an analysis of subthreshold behavior in transistors. Charge transport in shallow states can be described by multiple trap and release transport, while hopping transport models, such as variable range hopping or Gaussian disorder-based model, describe well the deeper state’s charge transport. In addition, the transition between the conduction regimes is a function of temperature and carrier density.

PURPOSES : While road networks are becoming increasingly complex, traffic signs are being indiscriminately installed and operated, which makes drivers who depend on traffic signs to reach their destination confused and unable to understand road information efficiently. In order to promptly and exactly guide road users to their destinations, traffic signs should be able to satisfy the functions of connectivity, visibility, and location suitability. However, the results of a site survey shows that most of the traffic signs currently installed in the Jeollanam-do Province do not satisfy these functions. METHODS : This study analyzed the problems of traffic signs after an actual site survey and focused on a total on 9,353 traffic signs and 70 road routes in Jeollanam-do Province. RESULTS : This study analyzed the problems of traffic signs based on their required functions (connectivity, visibility, suitability) and suggested improvements by establishing a guide system that considered the problems found in the study. CONCLUSIONS : The guide system can be utilized as a basic material that provides efficient road information for future installation and maintenance of traffic signs in Jeollanam-do Province.

We demonstrate high-performance single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) using the simple and robust method of an interacting fluoropolymer encapsulation with thermal annealing in vacuum to reduce the charge transfer. With an optimized combination of the fabrication process and the device configuration, drop-casted SWCNT-TFTs exhibit a field-effect mobility of $\sim 18$ cm2/ $\text{V}\,\cdot \, \text{s}$ in the linear regime, an ON–OFF-current ratio of $\sim 10^{6}$ , a threshold voltage of around 0 V, and a subthreshold swing of 97 mV/decade, which is among the best results that have been achieved in 2-D random networks of the SWCNTs. We also investigate the instability characteristics in the SWCNT-TFTs encapsulated with fluoropolymer during the prolonged electrical bias-stress. Interestingly, the drop in drain current of the SWCNT-TFTs was partially recovered with a second phenomenon that increases the drain current after a certain time. The hydrophobic surface that the fluoropolymer film possesses, reduced the chemical interaction of charge carriers with the hydroxyl (–OH) functional groups which act as defects in the SWCNT-TFTs.

Optimum cross-sectional shape of an automotive disc brake was developed based on FEM thermal analyses and the Taguchi method. Frictional heat flux and convection heat transfer coefficients were first calculated using equations and applied to the disc to calculate accurate temperature distribution and thermal deformations under realistic braking conditions. Maximum stress was generated in an area with highest temperature under pads and near the hat of ventilated disc and vanes. The SN ratio from Taguchi method and MINITAB was applied to obtain the optimum cross-sectional design of a disc brake on the basis of thermal deformations. The optimum cross-section of a disc can reduce thermal deformation by 15.2 % compared to the initial design.

The rapid and dense assembly of solution-processed single-wall carbon nanotube (SWCNT) semiconducting films is the key enabling factor for their practical applications to large-area electronics and potentially, roll-to-roll based process development. In this study, we demonstrate a significant reduction in the assembly time for a commercial nanotube dispersion (95%-purified semiconducting SWCNT ink), whilst maintaining a high-quality film with better density, by adding a ∼0.1% volume ratio of nitric acid to the dispersion. A rapidly and densely assembled film was formed after deposition for less than 30 seconds, compared to more than several minutes in a commercial reference ink as previously reported by many research groups. The relationships among the zeta potential, pH concentration, and deposition time of the engineered dispersion were also investigated. The electrostatically weakened force of the ionic surfactants in the engineered inks leads to the rapid formation of densely packed SWCNT films, thereby enabling the fabrication of high-performance SWCNT thin film transistors (TFTs) with a field-effect mobility of 18.80 ± 2.08 cm2 V−1 s−1 and on/off ratios of ≥104 in a significantly reduced process time.

We demonstrate high-performance field-effect transistors consisting of hybrid graphene/fluoropolymer films by investigating the molecular interaction with strong carbon–fluorine dipoles and hydrophobic surface characteristics. A simple and reproducible solution-coating method on a chemical vapor deposition grown monolayer graphene was employed with fluoropolymer, amorphous CYTOP, and polycrystalline poly(vinylidene fluoride-co-trifluoroethylene) as an interacting layer. All of the key device metrics, including field-effect mobility, Dirac voltage, residual carrier concentration, ON–OFF current ratio, and electron–hole transport symmetry, were substantially improved. Significantly, the Dirac voltage shifted in both directions toward zero, regardless of its initial positions of the Dirac voltage after molecular encapsulation with fluoropolymers. We also demonstrate the improved stability of hybrid graphene/fluoropolymer films that possesses a hydrophobic surface through repelling hydroxyl (–OH) functional groups from the graphene surface.

We report the effects of interfacial dielectric layers on the field-effect mobility of thin-film transistors (TFTs) with sol-gel based amorphous indium-gallium-zinc oxide (IGZO) films on thermally-grown silicon dioxide (SiO2) and sol-gel based zirconium dioxide (ZrO2) dielectrics. When the field-effect mobility as a function of the channel carrier concentration was extracted, the SiO2 based IGZO-TFT exhibited higher mobility than the ZrO2 based IGZO-TFT at a low carrier concentration. However, the field-effect mobility of the ZrO2 based IGZO-TFT increased as the gate charges increasing due to the gate bias applied. We also investigate the effects of interfacial dielectric layers on the charge transport characteristics in IGZO-TFTs by conducting temperature-dependent field-effect mobility measurements in the temperature range of 120 – 300 K. By analyzing an Arrhenius plot of the results, we confirm that the charge transport of IGZO-TFTs is dominant by the multiple-trapping-and-release model and discuss the effective mobility, which is significantly affected by the interfacial trap level and channel carrier concentration. Finally, we investigate the figure of merit and the activation energy of IGZO-TFTs with ZrO2 dielectrics fabricated by the optimized solution-process developed in this study through comparisons with other sol-gel based amorphous metal-oxide TFTs reported in the literature.

In this paper, flexible resistive random access memory (ReRAM) operating at 4 V with sol-gel based zirconium oxide (ZrO2) film at 200 °C is demonstrated. The memory performance of solution-processed ReRAM can be improved by utilizing oxygen-annealing, which results in high-quality metal-oxide dielectric films with suppressed oxygen vacancies. The effects of oxygen-annealing on metal-oxide bonding states are investigated to explain the origin of the improved switching performance in ReRAM. In addition, the conduction mechanism underlying the charge transport in solution-processed ReRAM by oxygen-annealing at 200 °C is investigated in a comparison to that of ReRAM annealed at 400 °C in air. The activation energy of solution-processed ReRAM is determined by an Arrhenius plot from temperature-dependent measurements in the range of 120–300 K. Finally, highly stable and robust flexible ReRAM without a passivation film against cyclic bending tests with curvature radiuses of 10 to 5 mm is demonstrated. We believe that this work provides a practical and effective approach by which to improve the device performance of ReRAM with sol-gel based metal-oxide dielectrics through oxygen-annealing at low temperature, compatible with flexible substrates.

High-performance flexible pH sensors based on nanocomposites of single-wall carbon nanotubes (SWCNTs) and Nafion, fabricated by screen printing on flexible substrates in ambient air are demonstrated. The electrical characteristics and thus the sensing performance of the pH sensors monitoring the change in resistance of printed nanocomposite films in a wide range of pH from 1 to 12 were controlled by the number of printed layers in multi-patterns. The operational stability of the flexible pH sensors was nearly unchanged after 200 cycles of bending tests having a curvature radius of 5 mm, which is essential for intergration of flexible pH sensors into wearable nanoelectronics. The sensing mechanism of the chemiresistive pH sensors based on nanocomposites is investigated in terms of chemical reaction. The hydrogen or hydroxide ions in the pH solution interact with the carbonyl and C H bonds bonds of the nanocomposite film, which induces or withdraws positively charged carriers, respectively. In addition, a real-time pH sensor system integrated into a drone application with wireless communication and data transmitting modules is demonstrated for the simultaneous visualization of processed data and remote detection of targets on the user's smartphone based on a designed Android algorithm.

During the fabrication processes for single-wall carbon nanotube thin-film transistors (SWCNT-TFTs), the impurities of organic residues such as photoresist and developer can be induced, which affects the charge transport. As a result, solution-processed SWCNT-TFTs exhibit poor and non-uniform device performance regardless of the intrinsic electrical characteristics. Here, we demonstrate a patterning technique using a selective surface treatment with solution-processed hydrophobic fluorocarbon copolymer in SWCNT-TFTs. By using the difference of wettability in a selective area, a channel region in SWCNT-TFTs can be patterned without the conventional photolithography and etching process. Furthermore, the optimized surface treatment results in denser random networks of SWCNTs in the channel patterned by such technique, compared to the dropcasted SWCNT. The statistical results of the key device metrics such as mobility and threshold voltage extracted from 30 SWCNT-TFTs conclusively prove the improved device performance of SWCNT-TFTs fabricated by such pattering technique. We believe that this work can provide a promising route to stimulate the process innovation of fabrication for high performance solution-processed electronics based on SWCNT random networks.

There have been constant attempts as regards high-performance thin-film transistors (TFTs) by improving the charge injection between the source/drain electrode (S/D) and the channel. In this paper, we investigate the effect of the electric contact on the device performance of single-wall carbon nanotube (SWCNT) TFTs employing the suitable work function material. In order to realize the electric contacts for the dominant hole injection between the S/D and the SWCNT active channel, a high work function material of molybdenum trioxide (MoOx) fabricated by an optimized process are utilized. The contact resistance is extracted by plotting the width-normalized resistance of SWCNTTFT with Pd and MoOx contacts as a function of channel length. We also demonstrate low-voltage operating SWCNT TFTs on flexible polyimide substrates with the reduced electric contacts. Without a buffer film which has been widely used to improve the device performance of TFT on a flexible substrate, high-performance low-voltage operating SWCNT-TFTs were achieved.

We efficiently controlled surface morphology of planar inverted p-i-n MAPbI 3-x Cl x perovskite solar cells. Dense and pinhole-free perovskite films could be obtained through a dripping anti-solvent blended with chlorobenzene (CBZ) and phenyl-C 61 -butyric acid methyl ester (PCBM). Compared to the control group, conversion efficiency improved from 10.8 (CBZ washing) to 11.4% (blended washing). Main contribution by the blended washing is planarization of surface topography, which can improve shunt resistance and fill factor of photovoltaic devices.

In this paper, we demonstrate the highly sensitive carbon nanotube (CNT) sensors for the detection of sub-ppm nitric oxide (NO) gas operating at room temperature. Such achievement can be realized by functionalizing CNT thin films with amine-based polymers through a solution-process technology at low temperature. In addition to high sensitivity, functionalized CNT sensors exhibit high selectivity towards NO gas, which is an effective and practical factor for health-care monitoring nano-electronics. We also investigated the effect of a post-cleaning treatment on the sensing performance of functionalized CNT thin films for sub-ppm NO gas sensors. We believe that this work can open-up new routes to realize high performance human-interactive electronics for respiratory diseases detection in exhaled air.

In this paper, we investigate the origin of photo-induced instability in amorphous metal-oxide based thin-film transistors (oxide-TFTs) by exploring threshold voltage (Vth) shift in transfer characteristics. The combination of photo irradiation and prolonged gate bias stress enhanced the shift in Vth in amorphous hafnium-indium-zinc-oxide (a-HfIZO) TFTs. Such results stem from the extended trapped charges at the localized defect states related to oxygen vacancy which play a role in a screening effect on the electric field induced by gate voltage. We also demonstrate the chemically clean interface in oxide-TFTs by employing oxygen annealing which reduces the density of trap states, thereby resulting in improved photo-induced stability. We believe that this work stimulates the research society of transparent electronics by providing a promising approach to suppress photo-induced instability in metal-oxide TFTs.

This thesis aims to improve the safety of bicycle traffic for activating the use of bicycle, main means of non-powered and non-carbon transportation in order to cope with worldwide crisis such as climate change and energy depletion and to implement sustainable traffic system. In this regard, I analyzed the problem of bicycle roads currently installed and operated, and developed the bicycle accident forecasting model. Following are the processes for this. First, this study presented the current status of bicycle road in Korea as well as accident data, collect the data on bicycle traffic accidents generated throughout the country for recent 3 years (2009~2011) and analyzed the features of bicycle traffic accidents based on the data. Second, this study selected the variable affecting the number of bicycle accidents through accident feature analysis of bicycle accidents at Jeollanam-do, and developed accident forecast model using the multiple regression analysis of `SPSS Statistics 21`. At this time, the number of accidents due to extension per road types (crossing, crosswalk, other single road) was used. To verify the accident forecast model deduced, this study used the data on bicycle accident generated in Gwangju, 2011, and compared the prediction value with actual number of accidents. As a result, it was found out that reliability of accident forecast model was secured through reconciling with actual number of cases except certain data. Third, this study carried out field survey on the bicycle road as well as questionnaire on satisfaction of bicycle road and use of bicycle for analysis of bicycle road problems, and presented safety improvement measures for the problems deduced as well as bicycle activation plans. This study is considered to serve as the fundamental data for planning and reorganizing of bicycle road in the future, and expected to improve safety of bicycle users and to promote activation of bicycle use as the means of transportation.

In this study, the electrical characteristics of Ni-CNT-SiO2-SiC structured 4H-SiC MIS capacitors were investigated. The effect of CNTs in the gate/insulator interface have been characterized by C–V measurement at 300 to 500K and J–V have also been measured. The experimental flat-band voltage tends to change with or without CNTs. Current densities of both devices are observed a negligible difference up to 3 V. It has been found that adding CNTs and/or change of temperature can help to control the positive and/or negative flat-band voltage shift.

We investigate photo-induced instability in thin-film transistors (TFTs) consisting of amorphous indium-gallium-zinc-oxide (a-IGZO) as active semiconducting layers by comparing with hydrogenated amorphous silicon (a-Si:H). An a-IGZO TFT exhibits a large hysteresis window in the illuminated measuring condition but no hysteresis window in the dark condition. On the contrary, a large hysteresis window measured in the dark condition in a-Si:H was not observed in the illuminated condition. Even though such materials possess the structure of amorphous phase, optical responses or photo instability in TFTs looks different from each other. Photo-induced hysteresis results from initially trapped charges at the interface between semiconductor and dielectric films or in the gate dielectric which possess absorption energy to interact with deep trap-states and affect the movement of Fermi energy level. In order to support our claim, we also perform CV characteristics in photo-induced hysteresis and demonstrate thermal-activated hysteresis. We believe that this work can provide important information to understand different material systems for optical engineering which includes charge transport and band transition.

We report on the restoration of the electronic characteristics of waferscale chemical vapor deposition (CVD) monolayer graphene field-effect transistors (GFETs) by reducing the impurity concentration. An optimized electropolishing process on copper foils combined with carbon-fluorine encapsulation using a suitable amorphous fluoropolymer enables reducing the surface roughness of graphene and screening out interfacial impurity scattering, which leads to an improvement in all key device metrics. The conductivity at the Dirac point is substantially reduced, resulting in an increase in the on-off current ratio. In addition, the field-effect mobility increased from 1817 to 3918 cm2/V-s, the impurity concentration decreased from 1.1 × 1012 to 2.1 × 1011 cm−2 and the electron and hole transport became more symmetric. Significantly, favorable shifts toward zero voltage were observed in the Dirac point. We postulate that the smoother surface due to electropolishing and a pool of strong dipole-dipole moments in the flouropolymer coating provide a charge buffer that relaxes the fluctuation in the electron-hole puddles. We also investigate the long-term stability in GFETs encapsulated with fluoropolymer, which exhibit a high hydrophobicity that suppresses the chemical interaction with water molecules. Open image in new window

We have investigated tunable threshold voltage in solution-processed single-walled carbon nanotube thin-film transistors (SWCNT TFTs) employing a simple and reproducible method of chemical encapsulation. Compared to a pristine one, SWCNT TFTs encapsulated with ammonium hydroxide (NH4OH) and nitric acid (HNO3) exhibit a negative shift and a positive shift in threshold voltage, respectively. Such results can be explained by the modification of the energy band at the interface between the source metal electrode and the SWCNT network. By using the Y-function method, we also characterized electrical properties such as field-effect mobility, threshold voltage, and contact resistance for TFTs treated with NH4OH or HNO3. The technique to favorably tune threshold voltage in solution-processed SWCNTs is significant for constituting CNT-based nanoelectronics.

We investigated the aging effect on solution-processed InZnO thin-film transistors (TFTs) according to In:Zn composition ratio and exposure time in an air environment. In order to improve the aging effect, microwave irradiation (MWI) for post-deposition annealing was introduced as an alternative to conventional thermal annealing and both methods were compared. A dramatic shift in threshold voltage (Vth) and degradation in subthreshold slope values (SS) were observed in devices treated with thermal annealing, whereas the degradation was improved in devices treated with MWI annealing. The improved values were different according to the In:Zn composition ratio. The MWI annealing not only assists with intermolecular bonding, but also suppresses the formation of oxygen vacancy (VO) and the oxygen in hydroxide (MOH) from the X-ray photoelectron spectroscopy (XPS) analysis. The samples annealed by MWI exhibited superior long-term stability in an air environment as well as reliability against gate bias stress. We believe that MWI may be promising for fabrication of devices based on flexible and transparent electronics with the merits of low-temperature processing and excellent electrical performance.

Air-stable n-doping of carbon nanotubes is presented by utilizing SiN(x) thin films deposited by plasma-enhanced chemical vapor deposition. The fixed positive charges in SiN(x), arising from (+)Si ≡ N3 dangling bonds induce strong field-effect doping of underlying nanotubes. Specifically, an electron doping density of ∼ 10(20) cm(-3) is estimated from capacitance voltage measurements of the fixed charge within the SiN(x). This high doping concentration results in thinning of the Schottky barrier widths at the nanotube/metal contacts, thus allowing for efficient injection of electrons by tunnelling. As a proof-of-concept, n-type thin-film transistors using random networks of semiconductor-enriched nanotubes are presented with an electron mobility of ∼ 10 cm(2)/V s, which is comparable to the hole mobility of as-made p-type devices. The devices are highly stable without any noticeable change in the electrical properties upon exposure to ambient air for 30 days. Furthermore, the devices exhibit high uniformity over large areas, which is an important requirement for use in practical applications. The work presents a robust approach for physicochemical doping of carbon nanotubes by relying on field-effect rather than a charge transfer mechanism.

Adopting an efficient charge transport layer is crucial to improve the photovoltaic (PV) performances of organo-lead halide perovskite (PRV) solar cells. In this study, we suggest a novel hybrid hole-transport layer (HTL) consisting of single-walled carbon nanotubes (SWNTs) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) for inverted-planar PRV devices. The SWNTs were drop-cast on ITO/glass substrates, and they were partly grown perpendicular to the substrates. Then, we coated PEDOT:PSS to cover the SWNTs for complete electron-blocking. A PRV light-harvester was spin-cast on the hybrid HTL, and the vertical SWNTs protruded into the PRV through penetrating the PEDOT:PSS. Steady-state photoluminescence spectroscopy evidenced that the SWNTs/PEDOT:PSS hybrid HTL showed enhanced charge-carrier quenching properties. The hybrid HTL also revealed negligible parasitic absorption loss checked by UV-Vis spectroscopy. These contributed to improve the average power conversion efficiency from 9.4% to 11.0% (up to 12.5% for the best cell) based on fabricated 90 devices. Furthermore, significant suppression of current–voltage hysteresis was attained by employing the hybrid HTL. This study not only manifests unprecedented utilization of the SWNTs for the HTL in inverted planar PRV cells but also paves the way for the development of high-performance and reliable PRV solar cells compatible with flexible processing at low temperature (