Search

Abstract In this study, we introduce a flexible metal grid transparent electrode fabricated using a lift-off process. This transparent electrode consisting of metal thin film with punched-like pattern by hole array was fabricated with 8 um separations. The separation of inkjet-printed etching resistant ink droplets was controlled in order to investigate the relationship between its electrical and optical properties of the electrodes. The aluminum areal density was defined to predict the electrical and optical properties of different arrays. A high and uniform transmittance spectrum appears to extend broadly into the UV region. The figure of merit of the transparent electrode was investigated in order to determine its performance as a transparent electrode. Moreover, there was no significant change in the resistance after 7000 bending cycles, indicating that the array conductor had superior stability. We also demonstrate transparent touch screen panels fabricated using the transparent electrode.

Several electrode materials have been developed to provide high energy density and a long calendar life at a low cost for lithium-ion batteries (LIBs). Iron (III) vanadate (FeVO4), a semiconductor material that follows insertion/extraction chemistry with a redox reaction and provides high theoretical capacity, is an auspicious choice of anode material for LIBs. The correlation is investigated between calcination temperatures, morphology, particle size, physicochemical properties, and their effect on the electrochemical performance of FeVO4 under different binders. The crystallite size, particle size, and tap density increase while the specific surface area (SBET) decreases upon increasing the calcination temperature (500 °C, 600 °C, and 700 °C). The specific capacities are reduced by increasing the calcination temperature and particle size. Furthermore, FeVO4 fabricated with different binders (35 wt.% PAA and 5 wt.% PVDF) and their electrochemical performance for LIBs was explored regarding the effectiveness of the PAA binder. FV500 (PAA and PVDF) initially delivered higher discharge/charge capacities of 1046.23/771.692 mAhg−1 and 1051.21/661.849 mAhg−1 compared to FV600 and FV700 at the current densities of 100 mAg−1, respectively. The intrinsic defects and presence of oxygen vacancy along with high surface area and smaller particle sizes efficiently enhanced the ionic and electronic conductivities and delivered high discharge/charge capacities for FeVO4 as an anode for LIBs.

This study suggested the design of type-variable electronic paper with multiple bottom electrode structures and experimentally investigated the process mechanism of the electrophoretic particle loading method (EPLM) as an electronic ink injection method. The type-variable electronic paper was achieved by constructing the multi-electrode structure that had a structure of four electrodes that can independently apply voltage to one cell. By injecting electronic ink that mixes two types of particles with opposite charges into an electrically neutral color (blue) fluid, we realized electronic paper with a single color, and we then measured the optical characteristics of the panel. We used the EPLM to prevent charged particles that have lost their charge from being injected into the e-paper by using an electric field. In order to confirm the color expression and transmittance control effect using the multi-electrode structure, we conducted reflectance measurement and transmittance measurement experiments. Our experiments confirmed that the expression of more than five colors was possible and that the transmittance was controllable to a minimum of 13.50% and a maximum of 71.18%. This study provides an attractive method to create e-paper as a new form outside the framework of existing e-paper technology.

Organic-inorganic hybrid perovskite materials have attracted tremendous attention as a key material in various optoelectronic devices. Distinctive optoelectronic properties, such as a tunable energy band position, long carrier diffusion lengths, and high charge carrier mobility, have allowed rapid progress in various perovskite-based optoelectronic devices (solar cells, photodetectors, light emitting diodes (LEDs), and lasers). Interestingly, the developments of each field are based on different characteristics of perovskite materials which are suitable for their own applications. In this review, we provide the fundamental properties of perovskite materials and categorize the usages in various optoelectronic applications. In addition, the prerequisite factors for those applications are suggested to understand the recent progress of perovskite-based optoelectronic devices and the challenges that need to be solved for commercialization.

Optimization of ink-jet printing conditions of quantum-dot (QD) ink by cosolvent process and improvement of quantum-dot light-emitting diodes (QLEDs) characteristics assisted by vacuum annealing were analyzed in this research. A cosolvent process of hexane and ortho-dichlorobenzene (oDCB) was optimized at the ratio of 1:2, and ink-jetting properties were analyzed using the Ohnesorge number based on the parameters of viscosity and surface tension. However, we found that these cosolvents systems cause an increase in the boiling point and a decrease in the vapor pressure, which influence the annealing characteristics of the QD emission layer (EML). Therefore, we investigated QLEDs’ performance depending on the annealing condition for ink-jet printed QD EML prepared using cosolvents systems of hexane and oDCB. We enhanced the quality of QD EML and device performance of QLEDs by a vacuum annealing process, which was used to prevent exposure to moisture and oxygen and to promote effective evaporation of solvent in QD EML. As a result, the characteristics of QLEDs formed using ink-jet printed QD EML annealed under vacuum environment increased luminescence (L), current efficiency (CE), external quantum efficiency (EQE), and lifetime (LT50) by 30.51%, 33.7%, 21.70%, and 181.97%, respectively, compared to QLEDs annealed under air environment.

In this study, silicon nitride thin films are deposited on organic polyethylene-naphthalate (PEN) substrates by laser assisted plasma enhanced chemical vapor deposition (LAPECVD) at a low temperature (150 °C) for the purpose of evaluating the encapsulation performance. A plasma generator is placed above the sample stage as conventional plasma enhanced chemical vapor deposition (PECVD) configuration, and the excimer laser beam of 193 nm wavelength illuminated in parallel to the sample surface is coupled to the reaction zone between the sample and plasma source. Major roles of the laser illumination in LAPECVD process are to compete with or complement the plasma decomposition of reactant gases. While a laser mainly decomposes ammonia molecules in the plasma, it also contributes to the photolysis of silane in the plasma state, possibly through the resulting hydrogen radicals and the excitation of intermediate disilane products. It will also be shown that the LAPECVD with coupled laser illumination of 193 nm wavelength improves the deposition rate of silicon nitride thin film, and the encapsulation performance evaluated via the measurement of water vapor transmission rate (WVTR).

We report the local surface potential mapping of pentacene film prepared by physical vapor deposition with scanning kelvin probe microscopy where the sample is scanned under different gate voltages. Surface topography and the corresponding potential maps were obtained simultaneously. Spatial distribution of the surface potential at a low gate voltage is clearly correlated with topographic features. A lower electrostatic potential was measured at the grain boundaries (GBs), suggesting that GBs behave as hole traps. This observation is bolstered by conductive atomic force microscopy (C‐AFM) data, which reveals a higher conductivity within the grains as opposed to the GBs. An increase in gate voltage minimizes the potential differences at the grain and GBs, suggesting a modification in trap occupancy. We expect that these experimental results, along with existing theories, will provide a better understanding of the microstructural‐electrical properties of pentacene film. Research Highlights: Local surface potential mapping of pentacene film with scanning kelvin probe microscopy.Correlation between the surface potential map and topography at a low gate voltage.Decrease of the potential distribution inhomogeneity by the gate voltage increasement.Higher conductivity at inner grain than grain boundary in conductive atomic force microscopy. [ABSTRACT FROM AUTHOR]

Soft hydrated permeable surfaces of hydrogels exhibit unique lubrication behaviors, including frictional hysteresis found in tribo-rheometry measurements. A hydrogel lubrication model that describes the transient behavior was previously developed using the structure kinetics model in the field of rheology and rate-and-state friction model, where the friction change is described as a competition between buildup and breakdown rates. In this study, the model is further modified to include the effect of hydrophilicity of a countersurface. Ultraviolet (UV)/ozone treatment on an aluminum surface significantly removes organic materials, resulting in extremely hydrophilic surface. Friction response of a polyacrylamide hydrogel against untreated and UV/ozone-treated aluminum exhibited noteworthy difference in the trajectory of hysteresis. Model fits were conducted using the modified lubrication model on both hystereses, and the fitting parameters of both hystereses are compared with each other to identify a parameter addressing hydrophilicity. Based on the model fits, we suggest that the hydrophilicity of the countersurface initially prevents the adsorption on the hydrogel surface because it holds water better. However, once water goes out of the contact due to contact pressure, a stronger adsorption occurs, which increases friction and decreases the speed dependence of friction. [ABSTRACT FROM AUTHOR]

Several electrode materials have been developed to provide high energy density and a long calendar life at a low cost for lithium-ion batteries (LIBs). Iron (III) vanadate (FeVO4), a semiconductor material that follows insertion/extraction chemistry with a redox reaction and provides high theoretical capacity, is an auspicious choice of anode material for LIBs. The correlation is investigated between calcination temperatures, morphology, particle size, physicochemical properties, and their effect on the electrochemical performance of FeVO4 under different binders. The crystallite size, particle size, and tap density increase while the specific surface area (SBET) decreases upon increasing the calcination temperature (500 °C, 600 °C, and 700 °C). The specific capacities are reduced by increasing the calcination temperature and particle size. Furthermore, FeVO4 fabricated with different binders (35 wt.% PAA and 5 wt.% PVDF) and their electrochemical performance for LIBs was explored regarding the effectiveness of the PAA binder. FV500 (PAA and PVDF) initially delivered higher discharge/charge capacities of 1046.23/771.692 mAhg−1 and 1051.21/661.849 mAhg−1 compared to FV600 and FV700 at the current densities of 100 mAg−1, respectively. The intrinsic defects and presence of oxygen vacancy along with high surface area and smaller particle sizes efficiently enhanced the ionic and electronic conductivities and delivered high discharge/charge capacities for FeVO4 as an anode for LIBs. [ABSTRACT FROM AUTHOR]

In this work, we introduce an indirect X‐ray detector with organic photodiode (OPD). OPD, as a photodetector, is attractive due to its easy fabrication of even large area or flexible form factor. The top electrode of OPD is fabricated with a translucent organic‐metal‐organic (OMO) structure to absorb more light energy by the surface plasmonic effect at the organic‐metal interface. In addition, the new fabricated OPD has a microcavity effect, which is generated between the top and bottom electrodes, makes the broad absorption spectrum of CuPc (active layer) narrower, and tune to the narrow Gd2O2S scintillator emission wavelength. Through X‐ray experiments, the microcavity effect was shown to be useful and controllable by varying the thickness of C60 in the bulk heterojunction (BHJ) structure of the active layers which are composed of C60 and CuPc. [ABSTRACT FROM AUTHOR]

Summary: Halide perovskite solar cells (PSCs) have gained enormous attention due to their favorable features such as bandgap tunability, considerable free carrier diffusion length, low‐cost fabrication, and comparable efficiency to that of conventional silicon solar cells. Among several PSCs' structures, the inverted structure is the most suitable candidate for diverse portable applications since they can take advantage of the previously developed organic solar cells' structure. However, the single transporting layer system of the inverted‐structured PSCs makes it challenging to achieve high efficiency and operational stability. Here, we introduce a unique transporting layer system that adopts 8‐hydroxyquinolinolato‐lithium (Liq) as a buffer layer at the interface between [6,6]‐phenyl C71 butyric acid methyl ester (PC70BM) and Ag electrode. By introducing the Liq, we effectively decreased the potential energy barrier and iodide accumulation at the interface between PC70BM and Ag electrode, which resulted in an efficient and stable PSC. In the optimized structure, the power conversion efficiency and stability (T80) increased from 9.5% and 100 h to 10.13% and 200 h, respectively. [ABSTRACT FROM AUTHOR]

Silicon nitride thin film was fabricated using laser‐assisted plasma‐enhanced chemical vapor deposition (LAPECVD) with 193 nm ArF excimer laser. In order to achieve damage‐resistive and reliable thin film encapsulation, the deposition of silicon nitride was performed in two‐step that laser‐assisted CVD (LACVD) and LAPECVD performed on the LACVD thin film. [ABSTRACT FROM AUTHOR]

Fabricating an electron extraction layer (EEL) with a metal doping transition metal oxide (TMO) in inorganic–organic hybrid perovskite solar cells (PeSCs) and organic solar cells (OSCs) is a simple and efficient process for enhancing photovoltaic properties. Here, the universal benefits and common factors that influence both PeSCs and OSCs as a result of changes in Al‐doped TiO2 properties are investigated. These common factors are identified in two separate mechanisms. The first involves surface smoothing of TiO2 films, which affects the formation of a high crystalline active layer and reduces recombination between the electron extraction and active layers. The second involves bandgap widening of TiO2, which reduces the activation energy and enhances the quenching efficiency of devices. These factors are demonstrated in various measurements. The results will help in understanding the fundamental benefits of Al‐doped TiO2 in solution‐processed thin‐film solar cells. [ABSTRACT FROM AUTHOR]

We fabricated an organic light emitting diode using poly(9‐vinylcarbazole) : tris[2‐(p‐tolyl)pyridine]iridium(III) emitting layer fabricated by nozzle jet printing. Uniform thin films were formed onto both of glass and PEN substrate. Bending test of the flexible OLEDs was also demonstrated and its performance was stably maintained until 300 cycles of bending. [ABSTRACT FROM AUTHOR]

We demonstrate ZnO nanowire based UV sensor by laser-induced hydrothermal growth of ZnO nanowire. By inducing a localized temperature rise using focused laser, ZnO nanowire array at ~15 μm size consists of individual nanowires with ~8 μm length and 200~400 nm diameter is readily synthesized on gold electrode within 30 min at the desired position. The laser-induced growth process is consecutively applied on two different points to bridge the micron gap between the electrodes. The resultant photoconductive Zn ONW interconnections display 2~3 orders increase in the current upon the UV exposure at a fixed voltage bias. It is also confirmed that the amount of photocurrent can be easily adjusted by changing the number of ZnO NW array junctions. The device exhibits clear response to the repeated UV illumination, suggesting that this process can be usefully applied for the facile fabrication of low-cost UV sensor array. [ABSTRACT FROM AUTHOR]

Organic-inorganic hybrid perovskite materials have attracted tremendous attention as a key material in various optoelectronic devices. Distinctive optoelectronic properties, such as a tunable energy band position, long carrier diffusion lengths, and high charge carrier mobility, have allowed rapid progress in various perovskite-based optoelectronic devices (solar cells, photodetectors, light emitting diodes (LEDs), and lasers). Interestingly, the developments of each field are based on different characteristics of perovskite materials which are suitable for their own applications. In this review, we provide the fundamental properties of perovskite materials and categorize the usages in various optoelectronic applications. In addition, the prerequisite factors for those applications are suggested to understand the recent progress of perovskite-based optoelectronic devices and the challenges that need to be solved for commercialization. [ABSTRACT FROM AUTHOR]

Optimization of ink-jet printing conditions of quantum-dot (QD) ink by cosolvent process and improvement of quantum-dot light-emitting diodes (QLEDs) characteristics assisted by vacuum annealing were analyzed in this research. A cosolvent process of hexane and ortho-dichlorobenzene (oDCB) was optimized at the ratio of 1:2, and ink-jetting properties were analyzed using the Ohnesorge number based on the parameters of viscosity and surface tension. However, we found that these cosolvents systems cause an increase in the boiling point and a decrease in the vapor pressure, which influence the annealing characteristics of the QD emission layer (EML). Therefore, we investigated QLEDs' performance depending on the annealing condition for ink-jet printed QD EML prepared using cosolvents systems of hexane and oDCB. We enhanced the quality of QD EML and device performance of QLEDs by a vacuum annealing process, which was used to prevent exposure to moisture and oxygen and to promote effective evaporation of solvent in QD EML. As a result, the characteristics of QLEDs formed using ink-jet printed QD EML annealed under vacuum environment increased luminescence (L), current efficiency (CE), external quantum efficiency (EQE), and lifetime (LT50) by 30.51%, 33.7%, 21.70%, and 181.97%, respectively, compared to QLEDs annealed under air environment. [ABSTRACT FROM AUTHOR]

• Direct measurement of residual solvent in printed organic thin films • Decrease in amount of residual solvent when dried at high temperature and nitrogen environment • Troubling in triplet energy transfer at phosphorescent emitter by the polaronic effect of residual solvent molecules • Limited efficiency of organic light emitting diodes (OLEDs) by high amount of residual solvent. Using printed organic materials to fabricate organic light emitting diodes (OLEDs) is a low-cost process and one of the most innovative deposition technologies. Nozzle jet printing is a facile method with the advantages of high speed and large area fabrication. However, the printing process leaves residual solvent in the deposited organic films. How that remaining solvent affects the performance of the OLEDs, and the fundamental mechanism of that effect, is still unclear. In this study, we investigated the effect of residual solvent in a jet printed phosphorescent emissive layer. Gas chromatography-mass spectrography (GC–MS) was used to measure the amount of residual solvent, which was dependent on the film drying environment. The printed phosphorescent films exhibited weak intersystem crossing and decreased coupling between the vibrational states of the tris[2-(p-tolyl)pyridine]iridium(III) (Ir(mppy) 3) in measurements of ultraviolet–visible absorption (UV–vis Abs), photoluminescence (PL), and electroluminescence (EL). The deterioration of the photophysical characteristics of the phosphorescence was attributed to the polaronic effect of the residual solvent molecules. The dipoles of the solvent molecules influenced the orbitals of surrounding organic molecules, and those perturbations induced nonradiative relaxation of the excitons. There was no shift in the peaks, but the intensities of the photophysical measurements decreased, indicating that the deterioration in phosphorescence was not chemical degradation. Finally, when the amount of residual solvent increased, the current density and the efficiency of the fabricated OLED decreased. The residual solvent also resulted in efficiency roll-off at high luminance in the devices. [ABSTRACT FROM AUTHOR]

In this study, silicon nitride thin films are deposited on organic polyethylene-naphthalate (PEN) substrates by laser assisted plasma enhanced chemical vapor deposition (LAPECVD) at a low temperature (150 °C) for the purpose of evaluating the encapsulation performance. A plasma generator is placed above the sample stage as conventional plasma enhanced chemical vapor deposition (PECVD) configuration, and the excimer laser beam of 193 nm wavelength illuminated in parallel to the sample surface is coupled to the reaction zone between the sample and plasma source. Major roles of the laser illumination in LAPECVD process are to compete with or complement the plasma decomposition of reactant gases. While a laser mainly decomposes ammonia molecules in the plasma, it also contributes to the photolysis of silane in the plasma state, possibly through the resulting hydrogen radicals and the excitation of intermediate disilane products. It will also be shown that the LAPECVD with coupled laser illumination of 193 nm wavelength improves the deposition rate of silicon nitride thin film, and the encapsulation performance evaluated via the measurement of water vapor transmission rate (WVTR). [ABSTRACT FROM AUTHOR]

In this work, operationally and mechanically stable organic field‐effect transistors (OFETs) are demonstrated on aramid fiber‐based paper enabled by a simple and universal surface planarization method. By employing a nanoimprint lithography‐inspired surface smoothening method, rough aramid paper is successfully smoothened from a scale of several tens of micrometers to a sub‐nanometer‐scale surface roughness. Owing to the sub‐nanometer‐scale surface roughness of the aramid paper, the OFETs fabricated on the aramid paper exhibit decent field‐effect mobility (0.25 cm2 V−1 s−1) with a high current on‐to‐off ratio (>107), both of which are comparable with those of OFETs fabricated on rigid silicon substrates. Moreover, the OFETs fabricated on the aramid paper exhibit both high operational and mechanical stability; this is indicated by a bias‐stress‐induced threshold voltage shift (∆VTH ≈ 4.27 V under an excessive gate bias stress of 1.7 MV cm−1 for 1 h 30 min) comparable to that of OFETs on a rigid silicon substrate, moderate field‐effect mobility, and a threshold voltage stability under 1000 bending cycles with a compressive strain of 1%. The demonstration of highly stable OFETs on paper enabled by the simple planarization method will expand the potential use of various types of paper in electronic applications. [ABSTRACT FROM AUTHOR]

We demonstrate the improvement in the efficiency of planar heterojunction perovskite solar cells by employing cadmium selenide tetrapods (CdSe TPs) as an electron extraction layer. The insertion of the CdSe TP layer between the titanium oxide (TiO2) and perovskite film facilitates electron transfer at the TiO2/perovskite interface, as indicated by the significantly quenched steady-state photoluminescence of the perovskite film. Furthermore, we observed a conductivity enhancement of the perovskite film by introducing the CdSe TP layer. The combination of both effects induced by the TPs leads to enhancement in the carrier extraction as well as decreased recombination losses in the perovskite solar cells. As a result, an efficiency of 13.5% (1 sun condition) is achieved in the perovskite solar cells that incorporate the CdSe TP layer, which is 10% higher than that of the device without the CdSe TP layer. [ABSTRACT FROM AUTHOR]

In this paper, a 4H-SiC trench MOS barrier Schottky (TMBS) rectifier with an enhanced sidewall layer (ESL) is proposed. The proposed structure has a high doping concentration at the trench sidewall. This high doping concentration improves both the reverse blocking and forward characteristics of the structure. The ESL–TMBS rectifier has a 7.4% lower forward voltage drop and a 24% higher breakdown voltage. However, this structure has a reverse leakage current that is approximately three times higher than that of a conventional TMBS rectifier owing to the reduction in energy barrier height. This problem is solved when ESL is used partially, since its use provides a reverse leakage current that is comparable to that of a conventional TMBS rectifier. Thus, the forward voltage drop and breakdown voltage improve without any loss in static and dynamic characteristics in the ESL–TMBS rectifier compared with the performance of a conventional TMBS rectifier. [ABSTRACT FROM AUTHOR]