Yoon-Chae Nah

Roll-to-Roll sputtered ITO/Cu/ITO multilayer electrode for flexible, transparent thin film heaters and electrochromic applications.

We fabricate high-performance, flexible, transparent electrochromic (EC) films and thin film heaters (TFHs) on an ITO/Cu/ITO (ICI) multilayer electrode prepared by continuous roll-to-roll (RTR) sputtering of ITO and Cu targets. The RTR-sputtered ICI multilayer on a 700 mm wide PET substrate at room temperature exhibits a sheet resistance of 11.8 Ω/square and optical transmittance of 73.9%, which are acceptable for the fabrication of flexible and transparent EC films and TFHs. The effect of the Cu interlayer thickness on the electrical and optical properties of the ICI multilayer was investigated in detail. The bending and cycling fatigue tests demonstrate that the RTR-sputtered ICI multilayer was more flexible than a single ITO film because of high strain failure of the Cu interlayer. The flexible and transparent EC films and TFHs fabricated on the ICI electrode show better performances than reference EC films and TFHs with a single ITO electrode. Therefore, the RTR-sputtered ICI multilayer is the best substitute for the conventional ITO film electrode in order to realize flexible, transparent, cost-effective and large-area EC devices and TFHs that can be used as flexible and smart windows.

Pseudocapacitive Desalination of Brackish Water and Seawater with Vanadium-Pentoxide-Decorated Multiwalled Carbon Nanotubes

A hybrid membrane pseudocapacitive deionization (MPDI) system consisting of a hydrated vanadium pentoxide (hV2 O5 )-decorated multi-walled carbon nanotube (MWCNT) electrode and one activated carbon electrode enables sodium ions to be removed by pseudocapacitive intercalation with the MWCNT-hV2 O5 electrode and chloride ion to be removed by non-faradaic electrosorption of the porous carbon electrode. The MWCNT-hV2 O5 electrode was synthesized by electrochemical deposition of hydrated vanadium pentoxide on the MWCNT paper. The stable electrochemical operating window for the MWCNT-hV2 O5 electrode was between -0.5 V and +0.4 V versus Ag/AgCl, which provided a specific capacity of 44 mAh g-1 (corresponding with 244 F g-1 ) in aqueous 1 m NaCl. The desalination performance of the MPDI system was investigated in aqueous 200 mm NaCl (brackish water) and 600 mm NaCl (seawater) solutions. With the aid of an anion and a cation exchange membrane, the MPDI hybrid cell was operated from -0.4 to +0.8 V cell voltage without crossing the reduction and oxidation potential limit of both electrodes. For the 600 mm NaCl solution, the NaCl salt adsorption capacity of the cell was 23.6±2.2 mg g-1 , which is equivalent to 35.7±3.3 mg g-1 normalized to the mass of the MWCNT-hV2 O5 electrode. Additionally, we propose a normalization method for the electrode material with faradaic reactions based on sodium uptake capacities.

Influence of structural deformation on dye-sensitized solar cells with anodically fabricated self-organized TiO2 nanotubes

In the present study, various lengths of self-organized TiO2 nanotubes (TNTs) with and without structural disorder were grown on a Ti-sheet by anodization of the sheet, and their photovoltaic performance was investigated by using them as photo-anodes in dye-sensitized solar cells (DSSCs). The common structural disorders of the nanotubes which are often encountered in TNTs based DSSCs and their influence on photovoltaic performance was investigated using scanning electron microscopy (SEM), X-ray diffraction and electrochemical impedance spectroscopy (EIS). SEM and EIS investigation showed that TiO2 nanotube arrays attached firmly and aligned perpendicularly without any structural disorder to the Ti-substrate could significantly improve the performance of DSSCs.

Fabrication of Photoelectrochromic Devices Composed of Anodized TiO2 and WO3 Nanostructures

Abstract In this study, we demonstrate the photoelectrochromic devices composed of TiO 2 and WO 3 nanostructuresprepared by anodization method. The morphology and the crystal structure of anodized TiO 2 nanotubes and WO 3 nan-oporous layers are investigated by SEM and XRD. To fabricate a transparent photoelectrode on FTO substrate, a TiO 2 nanotube membrane, which has been detached from Ti substrate, is transferred to FTO substrate and annealed at 450°Cfor 1 hr. The photoelectrode of TiO 2 nanotube and the counter electrode of WO 3 nanoporous layer are assembled andthe inner space is filled with a liquid electrolyte containing 0.5 M LiI and 5 mM I 2 as a redox mediator. The propertiesof the photoelectrochromic devices is investigated and Pt-WO 3 electrode system shows better electrochromic perform-ance compared toWO 3 electrode. Keywords: Electrochromism, Photoelectrochromic Devices, TiO 2 nanotubes, WO 3 nanoporous layers, Anodization ······························································································································· ·································································································

Roll-to-roll sputtered and patterned Cu2−xO/Cu/Cu2−xO multilayer grid electrode for flexible smart windows

We fabricated cost-effective Cu2−xO/Cu/Cu2−xO multilayer grid electrodes using roll-to-roll (RTR) sputtering and patterning processes for use as transparent and flexible electrodes in flexible smart windows. To optimize the patterned Cu2−xO/Cu/Cu2−xO multilayer grid, the electrical and optical properties of the Cu2−xO/Cu/Cu2−xO multilayer grid electrodes were investigated as a function of grid width and pitch, which directly influence the filling factor of the grid. At the optimized grid width of 16 and pitch of 600 μm, the Cu2−xO/Cu/Cu2−xO multilayer grid had a sheet resistance of 7.17 Ohm per square and an optical transmittance of 87.6%. In addition, the mechanical properties of the optimized Cu2−xO/Cu/Cu2−xO multilayer grid electrode was compared to those of brittle ITO electrodes to demonstrate its outstanding flexibility. To show the potential of the Cu2−xO/Cu/Cu2−xO multilayer grid for smart windows, we fabricated a flexible and transparent thin film heater (TFH) and a flexible electrochromic (EC) device, which are key components of smart windows. The low saturation voltage of the Cu2−xO/Cu/Cu2−xO grid-based TFH and the fast on–off performance of the Cu2−xO/Cu/Cu2−xO grid-based EC device indicates that the RTR-processed Cu2−xO/Cu/Cu2−xO multilayer grid is promising as a low-cost and large-area flexible transparent electrode for high-performance smart windows.

Well-defined alternative polymer semiconductor using large size regioregular building blocks as monomers: electrical and electrochemical properties

Regioregular polymer semiconductors have demonstrated a well-ordered micro-crystalline morphology in thin films due to better π-stacking orientation resulting in efficient charge transport. We propose an effective synthetic strategy to achieve well-defined regioregular alternative donor–acceptor (D–A) type conjugated polymers using large molecular weight regioregular monomers. Using this synthetic route, various conjugated moieties can be systematically introduced in a single polymer backbone, and we developed a regioregular alternative D–A polymer, coded rr-PBTTh, based on thiophene as electron donating and benzothiadiazole as electron withdrawing groups. This new polymer possesses a highly planar conjugated backbone due to regioregularity and S⋯O and S⋯F non-covalent intramolecular conformational locks. rr-PBTTh exhibits well-balanced ambipolar transport characteristics mainly due to the balanced D–A molecular structure, and shows promising electrochromic performance with coloration efficiency up to 321.7 cm2 C−1 and rapid response time below 0.5 s.

Electrodeposition of hydrated vanadium pentoxide on nanoporous carbon cloth for hybrid energy storage

Electrodeposition is a simple and effective method for the synthesis of disordered hydrated vanadium pentoxide (V2O5·nH2O). For the synthesis of energy storage electrodes with high power performance, electrodeposition of hydrated V2O5 inside carbon micropores is particularly attractive to synergize electric-double layer formation and lithium ion intercalation. Here, we demonstrate that hydrated V2O5 can be effectively electrodeposited in carbon micropores of activated carbon cloth. Our study indicates that carbon pores larger than 1 nm are essential for the effective decoration with hydrated V2O5. A thermal treatment after the electrodeposition is often used to enhance the crystal structure of hydrated V2O5. However, thermal annealing of the hydrated vanadium pentoxide decorated activated carbon cloth under an oxygen-rich environment at high temperature (>330 °C) leads to a significant loss of pore volume, leading to a decreased electrochemical performance. At low annealing temperature (200 °C), the vanadium pentoxide electrodeposited activated carbon cloth electrode exhibits a maximum specific capacity of 137 mA h g−1 with stable cycle performance over 1600 cycles at a rate of 4C.

A facile approach for carburization of anodically grown titania nanotubes: towards metallization of nanotubes

The present work demonstrates a facile, low cost and environmentally friendly technique for carburization of TiO2 nanotubes. XRD and XPS investigations suggest that the anodically grown self-organized TiO2 nanotubes when annealed in an argon filled steel nut–bolt cavity working as an autogenic pressure reactor undergo carburization at 650 °C, which converts TiO2 into TiOyCz. TEM-SAED suggests that the carburized nanotubes are polycrystalline, and also contain some reduced oxides of titanium. The conductivity measurement of the carburized nanotubes shows their conductivity to be close to metals. The electrochemical investigation of the carburized nanotubes demonstrates that the material can be used as a conductive electrode material for electrochemical reactions.

Effects of Sputter Parameters on Electrochromic Properties of Tungsten Oxide Thin Films Grown by RF Sputtering

Abstract The electrochromic properties of tungsten oxide films grown by RF sputtering were investigated. Among the sputterparameters, first the Ar:O 2 ratios were controlled with division into only an O 2 environment, 1:1 and 4:1. The structure of eachfilm prepared by these conditions was studied by X-ray diffraction, X-ray photoelectron spectroscopy and Rutherfordbackscattering spectroscopy. The sputter-deposited tungsten oxide films had an amorphous structure regardless of the Ar:O 2 ratios. The chemical compositions, however, were different from each other. The stoichiometric structure and low-density filmwas obtained at higher O 2 contents. Electrochemical tests were performed by cyclic voltammetry and chronoamperometry at0.05 M H 2 SO 4 solutions. The current density and charge ratio was estimated during the continuous potential and pulse potentialcycling at − 0.5 V and 1.8 V, respectively. The film grown in a higher oxygen environment had a higher current density anda reversible charge reaction during intercalation and deintercalation. The in-situ transmittance tests were performed by He-Nelaser (633 nm). At higher oxygen contents, a big transmittance difference was observed but the response speed was too slow.This was likely caused by higher film resistivity. Furthermore, the effect of sputtering pressure was also investigated. Thestructure and surface morphology of each film was observed by X-ray diffraction and scanning electron microscopy. A roughsurface was observed at higher sputtering pressure, and this affected the higher transmittance difference and coloration efficiency.Key wordstungsten oxide, RF sputtering, electrochromism.

Synthesis and Characterization of Tungsten Trioxide Films Prepared by a Sol-Gel Method for Electrochromic Applications

Abstract Tungsten trioxide thin films are successfully synthesized by a sol-gel method using tungsten hexachlorideas precursors. The structural, chemical, and optical properties of the prepared films are characterized by scanning elec-tron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-Vis spectrophotometry. The electrochem-ical and electrochromic properties of the films before and after heat treatment are also investigated by cyclicvoltammetry, chronoamperometry, and in situ transmittance measurement system. Compared to as-prepared films, heat-treated tungsten trioxide thin films exhibit a higher electrochemical reversibility of 0.81 and superior coloration effi-ciency of 65.7 cm 2 /C, which implies that heat treatment at an appropriate temperature is a crucial process in a sol-gelmethod for having a better electrochromic performance.Keywords: Electrochromism, Tungsten trioxide, Sol-gel, Heat treatment, Coloration efficiency ······························································································································· ·································································································