Large-scale transfer of Ag nanowires from PET to PC film using a roll-to-roll UV lamination process for a capacitive touch sensor.

Demand for flexible transparent sensors for futuristic cars is increasing since such sensors can enhance the freedom of design and aesthetic value in the interior of cars. Herein, we propose a unique roll-to-roll UV lamination process that can expedite large-scale Ag nanowire (AgNW) transfer for a flexible capacitive sensor, using a photocurable resin composed of an epoxy acrylate oligomer, a reactive monomer (1,6-hexanediol diacrylate), and a photoinitiator (1-hydroxycyclohexyl phenyl ketone). The acryl groups in the resin were rapidly crosslinked by UV irradiation, which facilitated the AgNWs transfer from a PET to a PC substrate with the speed of 1050 cm2 min-1 and enhanced the adhesion between the AgNWs and the PC substrate. Systematic experiments were performed to determine optimal fabrication parameters with respect to the UV dose, lamination pressure, and laser dicing conditions. At the optimal fabrication conditions, the sheet resistance of AgNWs on a PC film (PC-AgNW) was as small as 36.79 Ω sq-1, which was only 3.17% deviation from that on a PET film (PET-AgNW). Furthermore, the optical transmittance of the PC-AgNW exceeded 88% over the visible range, and it was greater than that of the PET-AgNW. Notably, the sheet resistance of the PC-AgNW was almost constant after 50 taping and peeling cycles, indicating remarkable adhesion to the substrate. Furthermore, a capacitive touch sensor was fabricated using the PC-AgNW, and its switching signals were presented with and without finger touch.

Fabrication of LuAG:Ce3+ Ceramic Phosphors Prepared with Nanophosphors Synthesized by a Sol-Gel-Combustion Method.

The aim of this study was to investigate properties of ceramic phosphors fabricated using nano Lu3Al5O12:Ce3+ phosphors produced with a sol-gel-combustion method. These nano Lu3Al5O12:Ce3+ phosphors had a size of about 200 nm, leading to high density when fabricated as a ceramic phosphor. We manufactured ceramic phosphors through vacuum sintering. Alumina powder was added to improve properties. We mounted the manufactured ceramic phosphor in a high-power laser beam projector and drove it to determine its optical performance. Ceramic phosphor manufactured according to our route will have a significant impact on the laser-driven lighting industry.

Electron transport and photosynthetic performance in Fragaria × ananassa Duch. acclimated to the solar spectrum modified by a spectrum conversion film.

Functional films have been used in greenhouses to improve the light environment for plant growth. Among them, a spectrum conversion film converting the green light of incident sunlight into red light has been reported to increase the crop productivity. However, the results are not always consistent, and the reasons for the improvement are not fully understood. The objectives of this study were to reveal the cumulative effects of a green-to-red spectrum conversion film (SCF) on the electron transport and photosynthetic performance of Fragaria × ananassa Duch. The photosynthetic efficiency, leaf optical properties, chlorophyll content, chlorophyll fluorescence, growth, and fruit qualities when the plant was grown under a transparent polyethylene film (PE) and SCF were evaluated. The sunlight modified by SCF did not change the leaf optical properties and chlorophyll content but significantly increased the chlorophyll fluorescence parameters related to reduction end electron acceptors at PSI acceptor side and the efficiency of electron transport. Without an increase in nonphotochemical quenching, the effective quantum yields of PSII and PSI of leaves grown under SCF were significantly higher than those parameters when grown under PE. Forty eight days after transplanting, the photosynthetic efficiency and photosynthetic rates of leaves and whole plants increased significantly under SCF compared to PE. The vegetative growth was not affected by SCF, but the fruit weight, sweetness, acidity, and firmness under SCF were significantly improved. These results indicated that sunlight modified by SCF stimulates electron flow and improves photosynthetic capacity and fruit quality of Fragaria × ananassa Duch.

Enhancement of Luminescence Efficiency of Y2O3 Nanophosphor via Core/Shell Structure.

We successfully fabricated Y2O3:RE3+ (RE = Eu, Tb, and Dy) core and core-shell nanophosphors by the molten salt method and sol-gel processes with Y2O3 core size of the order of 100~150 nm. The structural and morphological studies of the RE3+-doped Y2O3 nanophosphors are analyzed by using XRD, SEM and TEM techniques, respectively. The concentration and annealing temperature dependent structural and luminescence characteristics were studied for Y2O3:RE3+ core and core-shell nanophosphors. It is observed that the XRD peaks became narrower as annealing temperature increased in the core-shell nanophosphor. This indicates that annealing at higher temperature improves the crystallinity which in turn enhances the average crystallite size. The emission intensity and quantum yield of the Eu3+-doped Y2O3 core and core-shell nanoparticles increased significantly when annealing temperature is varied from 450 to 550 °C. No considerable variation was noticed in the case of Y2O3:Tb3+ and Y2O3:Dy3+ core and core-shell nanophosphors.

Luminescent down-shifting CsPbBr3 perovskite nanocrystals for flexible Cu(In,Ga)Se2 solar cells.

To overcome the parasitic absorption of ultraviolet (UV) light in the transparent conductive oxide (TCO) layer of flexible Cu(In,Ga)Se2 (CIGS) thin film solar cells, a CsPbBr3 perovskite nanocrystal based luminescent down-shifting (LDS) layer was integrated on CIGS solar cells fabricated on a stainless steel foil. The CsPbBr3 perovskite nanocrystal absorbs solar irradiation at wavelengths shorter than 520 nm and emits photons at a wavelength of 532 nm. These down-shifted photons pass the TCO layer without parasitic absorption and are absorbed in the CIGS absorber layer where they generate photocurrent. By minimizing the parasitic absorption in the TCO layer, the external quantum efficiency (EQE) of the CIGS solar cell with the CsPbBr3 perovskite nanocrystal layer is highly improved in the UV wavelength range between 300 and 390 nm. Additionally, in the wavelength range between 500 and 1100 nm, the EQE is improved since the surface reflectance of the CIGS device with the CsPbBr3 perovskite LDS layer was reduced. This is because the CsPbBr3 perovskite nanocrystal layer, which has an effective refractive index of 1.82 at a wavelength of 800 nm, reduces the large refractive index mismatch between air (nair = 1.00) and the TCO layer (nZnO = 1.96 at a wavelength of 800 nm). Both the short circuit current density and power conversion efficiency of the flexible CIGS solar cell integrated with the CsPbBr3 perovskite are improved by 4.5% compared with the conventional CIGS solar cell without the CsPbBr3 perovskite LDS layer.

Multi-bandgap Solar Energy Conversion via Combination of Microalgal Photosynthesis and Spectrally Selective Photovoltaic Cell.

Microalgal photosynthesis is a promising solar energy conversion process to produce high concentration biomass, which can be utilized in the various fields including bioenergy, food resources, and medicine. In this research, we study the optical design rule for microalgal cultivation systems, to efficiently utilize the solar energy and improve the photosynthesis efficiency. First, an organic luminescent dye of 3,6-Bis(4'-(diphenylamino)-1,1'-biphenyl-4-yl)-2,5-dihexyl-2,5-dihydropyrrolo3,4-c pyrrole -1,4-dione (D1) was coated on a photobioreactor (PBR) for microalgal cultivation. Unlike previous reports, there was no enhancement in the biomass productivities under artificial solar illuminations of 0.2 and 0.6 sun. We analyze the limitations and future design principles of the PBRs using photoluminescence under strong illumination. Second, as a multiple-bandgaps-scheme to maximize the conversion efficiency of solar energy, we propose a dual-energy generator that combines microalgal cultivation with spectrally selective photovoltaic cells (PVs). In the proposed system, the blue and green photons, of which high energy is not efficiently utilized in photosynthesis, are absorbed by a large-bandgap PV, generating electricity with a high open-circuit voltage (Voc) in reward for narrowing the absorption spectrum. Then, the unabsorbed red photons are guided into PBR and utilized for photosynthesis with high efficiency. Under an illumination of 7.2 kWh m-2 d-1, we experimentally verified that our dual-energy generator with C60-based PV can simultaneously produce 20.3 g m-2 d-1 of biomass and 220 Wh m-2 d-1 of electricity by utilizing multiple bandgaps in a single system.

Aggregation induced emission of diketopyrrolopyrrole (DPP) derivatives for highly fluorescent red films.

A large number of diketopyrrolopyrrole (DPP) compounds showing aggregation induced emission (AIE) have been reported in the past few years. However, although DPP compounds exhibited AIE and excellent luminescence properties, their luminescence properties in solid or film states were not much focused on. Here we synthesized and characterized a series of DPP compounds with triphenylamine (TPA) moieties to investigate the AIE properties in the solid film state depending on the functional groups (TPA, BTPA, and MTPA) attached to the TPA moieties. T2 and D2 thin films showed excellent fluorescence quantum yields of 31% and 26%, respectively, compared to an M2 thin film (9%). The restriction of an intramolecular rotation process could inhibit the aggregation induced quenching process and play a key role in achieving highly fluorescent molecules in the solid state.

Optical design of dental light using a remote phosphor light-emitting diode package for improving illumination uniformity.

The projection-type dental lighting based on the remote phosphor light-emitting diode (LED) package is designed to enhance uniformity of illuminance and correlated color temperature (CCT) on a target plane and to remove glare in the eyes of the patient. This dental lighting enables dentists to illuminate effectively the patient's mouth by increasing the inner area (50 mm×25 mm) described in ISO 9680. The optical module comprised of the LED package and optical lens is modeled to satisfy the inner area wider than 100 mm×50 mm and illuminance over 5,000 lx per the designed optical module. The fabricated prototype dental lighting contains four optical modules, and the maximum illuminance is 22,786 lx. The measured inner area is 105 mm×74 mm, and the ratio of inner area to outer area is about 76%. Also, the CCT variation is below 450 K in total illuminance pattern.

Simple modification of basic dyes with bulky &symmetric WCAs for improving their solubilities in organic solvents without color change.

A simple and easy solubility enhancement of basic dyes was performed with bulky and symmetric weakly coordinating anions (WCAs). The WCAs decreased the ionic character of the dyes by broadening the partial charge distribution and causing a screening effect on the ionic bonding. This new modification with WCAs has advantages in that it has no influence on the optical properties of the dyes. The solubilities of unmodified and modified dyes were tested in several organic solvents. X-ray powder diffraction patterns of the dyes were measured. Color films were prepared with the dyes and their color loci were analyzed to evaluate the optical properties. By the modification with WCAs, commercial basic dyes showed sufficient solubilities for be applied to various applications while preserving their superior optical properties.

Analysis and Characterization of Dye-Based Black Matrix Film of Low Dielectric Constant Containing Phthalocyanine and Perylene Dyes.

For liquid crystal display black matrices of low dielectric constant, greenish zinc phthalocyanine dye and reddish perylene dye exhibiting high solubility and thermal stability were employed to fabricate dye-based black matrices. The spectral, optical, thermal and dielectric properties of the dye-based black matrices were tested, and the surfaces of them were investigated using field emission scanning electron microscopy and atomic force microscopy. The dye-based black matrices had sufficiently low dielectric constants and showed satisfactory thermal stability and weaker light absorption property compared with black matrices containing carbon black, due to the low solubility of the dyes and dye aggregations after a post-baking process.

Improvement of phosphor modeling based on the absorption of Stokes shifted light by a phosphor.

We have found that the emission spectrum of phosphors measured in the powder state differs from that measured for a single phosphor. When the emission spectrum of the powder state is adopted in an optical simulation, the simulated optical properties e.g., the correlated color temperature, color rendering index, and chromaticity coordinates, show a remarkable discrepancy from those of the fabricated LED package. However, the discrepancy is significantly improved when the emission spectrum from a low concentration of phosphor in a silicone binder is employed. We suggest that the discrepancy originates from the absorption of Stokes shifted light by a phosphor.

Comparison between organic sensitizers containing stilbene and azo group as bridging unit for dye sensitized solar cells.

While azo dyes have been widely used in dye industry, the azo dyes have been seldom applied as sensitizers to dye sensitized solar cells. In this study, new metal-free organic sensitizers, ST and AZ, which are same structures except bridging units, were synthesized and evaluated. ST containing stilbene as bridging unit gave higher energy conversion efficiency than AZ containing azo group as bridging unit. As a result of density functional theory (DFT) calculations, ST displayed more localized frontier molecular orbitals at lowest unoccupied molecular orbital (LUMO) states than AZ.

Electrochemical and optical characterization of cobalt, copper and zinc phthalocyanine complexes.

New phthalocyanine (Pc) derivatives that include the alkyl group in ligand were synthesized based on three core metals such as zinc (Zn), copper (Cu), and cobalt (Co). Electrochemical behaviors and optical properties of the new phthalocyanine derivatives with ligand and different core metal were investigated by using cyclic voltammetry, UV-Visible (UV-Vis) spectroscopy and photoluminescence (PL) spectroscopy. In UV-Vis data, maximum values of 2H, Co, Cu, and Zn complexes were 708 nm and 677 nm, 686 nm, 684 nm, respectively.

Influence of solvent and bridge structure in alkylthio-substituted triphenylamine dyes on the photovoltaic properties of dye-sensitized solar cells.

Three new triphenylamine dyes that contain alkylthio-substituted thiophenes with a low bandgap as a π-conjugated bridge unit were designed and synthesized for organic dye-sensitized solar cells (DSSCs). The effects of the structural differences in terms of the position, number, and shape of the alkylthio substituents in the thiophene bridge on the photophysical properties of the dye and the photovoltaic performance of the DSSC were investigated. The introduction of an alkylthio substituent at the 3-position of thiophene led to a decrease in the degree of redshift and the value of the molar extinction coefficient of the charge-transfer band, and the substituent with a bridged structure led to a larger redshift than that of the open-chain structure. The introduction of bulky and hydrophobic side chains decreased the short-circuit photocurrent (J(sc)), which was caused by the reduced amount of dye adsorbed on TiO(2). This resulted in a decrease in the overall conversion efficiency (η), even though it could improve the open-circuit voltage (V(oc)) due to the retardation of charge recombination. Furthermore, the change in solvents for TiO(2) sensitization had a critical effect on the performance of the resulting DSSCs due to the different amounts of dye adsorbed. Based on the optimized dye bath and molecular structure, the ethylene dithio-substituted dye (ATT3) showed a prominent solar-to-electricity conversion efficiency of 5.20%.

Effect of five-membered heteroaromatic linkers to the performance of phenothiazine-based dye-sensitized solar cells.

Phenothiazine derivatives with various conjugated linkers (furan, thiophene, and 3,4-ethylenedioxythiophene) were synthesized and used in dye-sensitized solar cells to study the effect of conjugated linkers on device performance. Among them, one with furan as a conjugated linker showed a solar energy-to-electricity conversion efficiency (η) of 6.58%, an improvement of over 24% compared with the T2-1 reference cells' 5.29% under AM 1.5 G irradiation.

Lithium-induced supramolecular hydrogel.

We describe a novel anisotropic supramolecular gel made of cyclodextrin-dye, in which physical gelation is completed by lithium salt. Rheological experiment reveals the elastic behaviors of the hydrogel, and high ionic conductivity represents a good mobility of ions inside the gel matrix.

Wood-polyethylene composites using ethylene-vinyl alcohol copolymer as adhesion promoter.

Saw dust-reinforced linear low density polyethylene (LLDPE) (1:1) composites were prepared by using ethylene-vinyl alcohol copolymer (EVAL) as adhesion promoter to improve mechanical strength. To evaluate the optimum vinylalcohol (VA) content in EVAL, various EVAL samples containing different contents of VA were used. The tensile properties of saw dust-LLDPE composites were improved by using EVAL as adhesion promoter in place of ethylene-vinyl acetate copolymer (EVAc). The saw dust-LLDPE composites prepared with EVAL containing 15 mol% VA showed the maximum yield stress and modulus. The tensile stress increased with addition of EVAL up to 3wt% on the wood filler, and then leveled off in the range of 3-10 wt%. However, the elongation was decreased with increasing VA content. Hydrogen bonding interaction between saw dust and EVAL was detected by FT-IR spectra. When EVAL consisting with 15 mol% VA was used, good adhesion between saw dust and LLDPE matrix was confirmed by SEM fractography.