Recently, electrochromic devices (ECDs) have gathered increasing attention owing to their high color contrast and memory effect, which make them highly applicable to smart windows, auto-dimming mirrors, sensors, etc. Traditional ECDs have a sandwich structure that contains an electrochromic layer between two ITO substrates. These sandwich-type devices are usually fabricated through the lamination of two electrodes and followed by the injection of a liquid electrolyte in the inner space. However, this process is sometimes complex and time consuming. In this study, we fabricated ECDs with a lateral electrode structure that uses only an ITO substrate and an all-in-one electrochromic gel, which is a mixture of electrolyte and electrochromic material. Furthermore, we investigated the EC properties of the lateral-type device by comparing it with a sandwich-type device. The lateral-type ECD shows strong blue absorption as the applied voltage increases and has a competitive coloration efficiency compared to the sandwich-type device.

일반적으로 전기변색소자들은 전기변색물질, 전해질 그리고 상대전극물질로 구성되어 있다. 그 중에서, 상대전극물질은 소자의 장기전환 안정성 및 낮은 작동 전압 등과 같은 전기변색소자들의 성능을 향상하는데 매우 중요하다. 본 연구에서는 다이메틸 프탈레이트 기반 전기변색소자에 페로센과 카본 전극을 적용하고 그 성능을 테스트 하였다. 특히 카본 전극에서 우수한 장기전환 안정성이 구현되었다.

In this study, we synthesize tungsten oxide thin films by electrodeposition and characterize their electrochromic properties. Depending on the deposition modes, compact and porous tungsten oxide films are fabricated on a transparent indium tin oxide (ITO) substrate. The morphology and crystal structure of the electrodeposited tungsten oxide thin films are investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). X-ray photoelectron spectroscopy is employed to verify the chemical composition and the oxidation state of the films. Compared to the compact tungsten oxides, the porous films show superior electrochemical activities with higher reversibility during electrochemical reactions. Furthermore, they exhibit very high color contrast (97.0%) and switching speed (3.1 and 3.2 s). The outstanding electrochromic performances of the porous tungsten oxide thin films are mainly attributed to the porous structure, which facilitates ion intercalation/deintercalation during electrochemical reactions.

In this study, we demonstrate the photoelectrochromic devices composed of TiO2 and WO3 nanostructuresprepared by anodization method. The morphology and the crystal structure of anodized TiO2 nanotubes and WO3 nan-oporous layers are investigated by SEM and XRD. To fabricate a transparent photoelectrode on FTO substrate, a TiO2nanotube membrane, which has been detached from Ti substrate, is transferred to FTO substrate and annealed at 450°Cfor 1 hr. The photoelectrode of TiO2 nanotube and the counter electrode of WO3 nanoporous layer are assembled andthe inner space is filled with a liquid electrolyte containing 0.5 M LiI and 5 mM I2 as a redox mediator. The propertiesof the photoelectrochromic devices is investigated and Pt-WO3 electrode system shows better electrochromic perform-ance compared toWO3 electrode.

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 cm2/C, which implies that heat treatment at an appropriate temperature is a crucial process in a sol-gelmethod for having a better electrochromic performance.

3000Å~6000Å의 두께로 진공 증착한 WO3 박막의 광특성 및 일렉트로크로미즘에 대하여 연구하였다. 증착된 WO3 박막은 모두 무색 투명 하였으며 X-선회절 분석결과 비정질 상태로 밝혀졌으며, 비정질 WO3 박막의 굴절율은 가시광선 영격에서 1.9-2.1로, 광에너지 gap은 3.25eV로 나타났다. ITO투명전극/WO3박막/LiCIO4 ~propylene carbonate/백금 대향전극 구조를 갖는 일렉트로크로믹소자를 구성하여 일렉트로크로믹 특성을 조사하였다. WO3 박막의 coloration/과 bleaching현상은 LiCIO4~propylene carbonate유기전해질과 ITO투명전극으로 부터 Li+이온과 전자의 이중주입에 의하여 청색으로 나타났으며, 가역적으로 전기 화학적인 산화반응에 의하여 bleaching현상이 일어났다. Coloration과 bleaching현상, 광학밀도, 구동전압 및 응답속도 등의 일렉트로크로믹 특성은 WO3 박막의 증착조건, 전해액 농도, 투명전극의 sheet resistance 인가전압에 크게 의존하는 것으로 밝혀졌다.