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Achieving efficient electron transport is challenging owing to the large energy barrier between the conduction band of n-type metal oxide and the lowest unoccupied molecular orbital (LUMO) of the emissive layer in inverted polymer light-emitting diodes (PLEDs) or the active layer in inverted polymer solar cells (PSCs), which results in unbalanced charge transport, leading to low device efficiencies. Herein, we have demonstrated that the device performance could be enhanced in both PLEDs and PSCs by treating either the interface between the electron transport layer (ETL) and the emissive layer in PLEDs or the active layers with self-assembled dipole monolayer (SADM), ionic liquid molecules (ILM) and polar solvent (PS). The interface engineering results in a reduction of the energy barrier, which results in enhanced electron transport in both devices. Especially, optimized PLEDs and PSCs show an external quantum efficiency (EQE) of 1.38% and a power conversion efficiency (PCE) of 4.21%, which are enhanced by approximately 138- and 1.37-fold, respectively, compared to the reference devices

Annealing Effect of ZnO Seed Layer on Enhancing Photocatalytic Activity of ZnO/TiO 2

Zinc oxide (ZnO)/titanium dioxide (TiO2) nanorods have been synthesized via a hydrothermal method for ZnO nanorods and an electron-beam deposition for TiO2 nanorods. This work examined the effect of annealing ZnO seed layer on the photocatalytic activity of the ZnO/TiO2 nanorods which was determined from photodecomposition of methylene blue under UV irradiation. The photocatalytic activity of the ZnO/TiO2 nanorods was improved with increasing annealing temperature of the seed layer from 300°C to 500°C. Annealing the seed layer at 500°C showed the best photocatalytic activity resulting from high UV absorption ability, a large surface area with flower structure and copious oxygen defects which promote separation of electron-hole pairs reducing electron recombination. The prepared nanorods were characterized by field emission-scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), photoluminescence (PL), and UV-visible spectroscopy

Micro-Segregated Liquid Crystal Haze Films for Photovoltaic Applications: A Novel Strategy to Fabricate Haze Films Employing Liquid Crystal Technology

Herein, a novel strategy to fabricate haze films employing liquid crystal (LC) technology for photovoltaic (PV) applications is reported. We fabricated a high optical haze film composed of low-molecular LCs and polymer and applied the film to improve the energy conversion efficiency of PV module. The technique utilized to fabricate our haze film is based on spontaneous polymerization-induced phase separation between LCs and polymers. With optimized fabrication conditions, the haze film exhibited an optical haze value over 95% at 550 nm. By simply attaching our haze film onto the front surface of a silicon-based PV module, an overall average enhancement of 2.8% in power conversion efficiency was achieved in comparison with a PV module without our haze film

High-Performance Perovskite Light-emitting Diodes via Morphological Control of Perovskite Film

Solution-processable perovskite materials have garnered tremendous attention because of their excellent charge carrier mobility, possibility of a tunable optical bandgap, and high photoluminescence quantum efficiency (PLQE). In particular, the uniform morphology of a perovskite film is the most important factor in realizing perovskite light-emitting diodes (PeLEDs) with high efficiency and full-coverage electroluminescence (EL). In this study, we demonstrate highly efficient PeLEDs that contain a perovskite film with a uniform morphology by introducing HBr into the perovskite precursor. The introduction of HBr into the perovskite precursor results in a perovskite film with a uniform, continuous morphology because the HBr increases the solubility of the inorganic component in the perovskite precursor and reduces the crystallization rate of the perovskite film upon spin-coating. Moreover, PeLEDs fabricated using perovskite films with a uniform, continuous morphology, which were deposited using 6 vol% HBr in a dimethylformamide (DMF)/hydrobromic acid (HBr) cosolvent, exhibited full coverage of the green EL emission. Finally, the optimized PeLEDs fabricated with perovskite films deposited using the DMF/HBr cosolvent exhibited a maximum luminance of 3490 cd m(-2) (at 4.3 V) and a luminous efficiency of 0.43 cd A(-1) (at 4.3 V).ope

Effect of emergency medical service use on time interval from symptom onset to hospital admission for definitive care among patients with intracerebral hemorrhage: a multicenter observational study

Objective This study evaluated whether emergency medical service (EMS) use was associated with early arrival and admission for definitive care among intracerebral hemorrhage (ICH) patients. Methods Patients with ICH were enrolled from 29 hospitals between November 2007 and December 2012, excluding those patients with subarachnoid hemorrhage, traumatic ICH, and missing information. The patients were divided into four groups based on visit type to the definitive hospital emergency department (ED): direct visit by EMS (EMS-direct), direct visit without EMS (non-EMS-direct), transferred from a primary hospital by EMS (EMS-transfer), and transferred from a primary hospital without EMS (non-EMS-transfer). The outcomes were the proportions of participants within early (<1 hr) definitive hospital ED arrival from symptom onset (pS2ED) and those within early (<4 hr) admission from symptom onset (pS2AD). Adjusted odds ratios were calculated to determine the association between EMS use and outcomes with and without inter-hospital transfer. Results A total of 6,564 patients were enrolled. The adjusted odds ratios (95% confidence intervals) for pS2ED were 22.95 (17.73–29.72), 1.11 (0.67–1.84), and 7.95 (6.04–10.46) and those for pS2AD were 5.56 (4.70–6.56), 0.96 (0.71–1.30), and 2.35 (1.94–2.84) for the EMS-direct, EMS-transfer, and non-EMS-direct groups compared with the non-EMS-transfer group, respectively. Through the interaction model, EMS use was significantly associated with early arrival and admission among direct visiting patients but not with transferred patients. Conclusion EMS use was significantly associated with shorter time intervals from symptom onset to arrival and admission at a definitive care hospital. However, the effect disappeared when patients were transferred from a primary hospital

Spin crossover in the cyanide-bridged Mo(V)Mn(III) single-chain magnet containing Fe(II) cations

A 1D Mo(V)Mn(III) chain compound balanced by {Fe[ HC(3,5-Me(2)pz)(3)](2)}(2+) dications was prepared. This complex displays a typical single-chain magnet character associated with the Mo(V)Mn(III) chain and a spin crossover phenomenon arising from cationic Fe(II) subunits. The spin crossover behavior tends to slightly affect single-chain magnetic properties at low temperature.National Research Foundation of Korea; Korean Government[2011-0003264]; Ministry of Education, Science and Technology[NRF20110018396

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Department of Materials Science and EngineeringSecuring eco-friendly renewable energy is one of the essential tasks of modern society. Solar energy has been considered the most promising energy sources, as it is one the most abundant and evenly distributed eco-friendly, renewable energy sources. Solar cells are therefore key energy conversion devices in realizing a new era of eco-friendly renewable energy. Perovskite solar cells (PeSCs) are newly emerged thin-film solar cells that have undergone intensive research over the last 10 years owing to advantages such as the outstanding optoelectronic properties of metal halide perovskite materials and the potential low costs resulting from solution-based manufacturing at low temperatures. These semiconductor devices are composed of several layers, including a perovskite light-absorbing layer, charge extraction layers, electrodes, and substrates. Controlling the conditions in the interfaces between these layers is key to realizing the high-performance of PeSCs. Interfacial engineering is an effective way to solve critical problems such as compatibility issues surrounding the coating, high density of defects at the surface, and unfavorable energy level alignments at the interfaces between layers. The simplicity of semi-transparent PeSCs fabrication with transparent electrodes on top of the cell has led to semi-transparent PeSCs attracting attention for utilization in Building Integrated Photovoltaics (BIPV) and perovskite/Si tandem solar cells. Therefore, the aesthetic aspect of PeSCs is considered important, and the development of interlayers for use in semi-transparent PeSCs is a new requirement. In this study, we deal with the critical problems that can occur at the interfaces between the layers in PeSCs and the introduction of a well-designed interlayer for solving the problems at the interfaces. Different interlayers are newly developed for the three interfaces in PeSCs, allowing the realization of highly efficient and aesthetic semi-transparent PeSCs. Chapter 2 describes the development of conjugate polyelectrolytes (CPEs) that are synthesized based on poly(fluorene-co-phenylene) by varying the ionic density of the side-chains in each repeating unit. The effect of CPEs as an interlayer between the hydrophobic hole extraction layer and the perovskite layer is investigated in p-i-n structure PeSCs. CPEs have both a hydrophobic conjugated polymer backbone and hydrophilic ionic side chains in their structure. Amphiphilic CPEs improve the compatibility between the hydrophobic hole extraction layer and the hydrophilic perovskite solutions. Additionally, ions from the side chains of CPEs efficiently passivate the interfacial defects of the perovskite. The compatibilizing and defect passivating properties of CPE were further improved by optimizing the ionic density of the repeating units. In Chapter 3, polyethyleneimine (PEI) is introduced as an interlayer between the C60 electron extraction layer and the indium zinc oxide (IZO) transparent top electrode in semi-transparent PeSCs. PEI, which contains high number of amines, effectively reduces the surface tension between the C60 and IZO, resulting in the lateral growth of IZO on the C60 and lower interfacial resistance. In addition, PEI induces an interfacial dipole that forms between the C60 and the IZO, changing the energy level alignment so that it is more favorable for electron extraction. In Chapter 4, ethylene-vinyl acetate (EVA) is utilized as anti-reflection (AR) film at the interface between the IZO top transparent electrode and air. Texturing EVA with an inverted pyramid surface reduces the reflection occurring between the highly refractive IZO and the lowly refractive air. In addition, coloration of the semi-transparent PeSCs without the loss of absorption in the visible range and minimized PCE loss is possible by adding UV light downshifting dyes to the textured EVA film.clos

Efficient inverted organic light-emitting devices by amine-based solvent treatment

The efficiency of inverted polymer light-emitting diodes (iPLEDs) were remarkably enhanced by introducing spontaneously formed ripple-shaped nanostructure of ZnO (ZnO-R) and amine-based polar solvent treatment using 2-methoxyethanol and ethanolamine (2-ME+EA) co-solvents on ZnO-R. The ripple-shape nanostructure of ZnO layer fabricated by solution process with optimal rate of annealing temperature improves the extraction of wave guide modes inside the device structure, and 2-ME+EA interlayer enhances the electron injection and hole blocking and reduces exciton quenching between polar solvent treated ZnO-R and emissive layer. As a result, our optimized iPLEDs show the luminous efficiency (LE) of 61.6 cd A-1, power efficiency (PE) of 19.4 lm W-1 and external quantum efficiency (EQE) of 17.8 %. This method provides a promising method, and opens new possibilities for not only organic light-emitting diodes (OLEDs) but also other organic optoelectronic devices such as organic photovoltaics, organic thin film transistors, and electrically driven organic diode laser. &amp;#169; (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only