Ki-Yun Cho

All-solid-state electrochromic device composed of WO3 and Ni(OH)2 with a Ta2O5 protective layer

An all-solid-state electrochromic device composed of WO3 and Ni(OH)2 with a Ta2O5 protective layer was prepared by rf magnetron sputtering and lamination with a proton-conducting solid polymer electrolyte. This device had good durability, high transmittance modulation (18%–74%) and coloration efficiency (about 84 cm2 C−1), and good response times (8.5 and 18 s, respectively, during the bleaching and coloring processes). This indicates that Ta2O5 layers are electrochemically stable and can be used as protective layer for Ni(OH)2 as well as WO3.

Bleached state transmittance in charge-unbalanced all-solid-state electrochromic devices

The bleached state transmittance of a charge-unbalanced, complementary electrochromic (EC) device may show residual coloration due to the presence of residual charges. In this study, EC devices were fabricated with configurations G/ITO/Ni(OH)2/Ta2O5/H+–SPE/Ta2O5/WO3/ITO/G and G/ITO/NiOOH/Ta2O5/H+–SPE/Ta2O5/HWO3/ITO/G (G=glass, H+–SPE=proton-conducting solid polymer electrolytes, and ITO=indium tin oxide). These devices, referred to as EC1 and EC2, were initially fabricated from fully bleached EC layers and from fully colored EC layers, respectively. The change in electrochromic properties as a function of charge capacity ratio (R) for each device was then compared. In comparison to EC2 devices, EC1 devices provided better bleached-state transmittances and higher coloration efficiencies over a wider range of R, and were less sensitive to changes in R value. This may arise because the absorbance caused by the residual charges in the colored state is greater and more sensitive to the charge capacity ratio than that in the bleached state.The bleached state transmittance of a charge-unbalanced, complementary electrochromic (EC) device may show residual coloration due to the presence of residual charges. In this study, EC devices were fabricated with configurations G/ITO/Ni(OH)2/Ta2O5/H+–SPE/Ta2O5/WO3/ITO/G and G/ITO/NiOOH/Ta2O5/H+–SPE/Ta2O5/HWO3/ITO/G (G=glass, H+–SPE=proton-conducting solid polymer electrolytes, and ITO=indium tin oxide). These devices, referred to as EC1 and EC2, were initially fabricated from fully bleached EC layers and from fully colored EC layers, respectively. The change in electrochromic properties as a function of charge capacity ratio (R) for each device was then compared. In comparison to EC2 devices, EC1 devices provided better bleached-state transmittances and higher coloration efficiencies over a wider range of R, and were less sensitive to changes in R value. This may arise because the absorbance caused by the residual charges in the colored state is greater and more sensitive to the charge capacity ratio th...

Polymer-Laminated Electrochromic Devices Composed of WO3 and Ni ( OH ) 2 on Glass and PET Substrates

Polymer-laminated electrochromic devices composed of WO 3 and Ni(OH) 2 films were fabricated on indium tin oxide (ITO)-coated glass and polyethylene terephthalate (PET) substrates. In each of the devices, data on the transmittance modulance, coloration efficiency, and response time were collected. The transmittance modulation of the glass device was larger than that of the PET device because the large amount of charge was incorporated into each WO 3 and Ni(OH) 2 film in glass device. The coloration efficiency, however, was comparable between the two devices, with reversible charge movement and the absence of side reactions. The PET device showed a longer coloring/bleaching performance regardless of whether it had a lower ITO electrical sheet resistance compared to a glass device, which can be attributed to high interfacial charge-transfer resistance.

Effect of photoreactivity of polyimide on the molecular orientation of liquid crystals on photoreactive polymer/polyimide blends

We prepared blend alignment layers from polymethacrylate with coumarin side chains (PMA-g-coumarin) and polyimides for the orientation of liquid crystals (LCs) using linearly polarized ultraviolet (UV) irradiation. We used two different polyimides, namely 4,4′-(hexafluoro-isopropylidene) diphthalic anhydride-3,5-diamino-benzoic acid (6FDA-DBA) and pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA). It was found that the molecular orientation of the LC depended on the type of polyimide in the blend alignment layer. The thermal stability of the LC orientation was enhanced regardless of the type of polyimide, while the direction of LC orientation was different for each type of polyimide. The photoreactivity of the polyimide was a very important factor in determining the molecular orientation of the LC on the blend alignment layer. This may be attributed to the different mechanisms of LC orientation on PMA-g-coumarin and polyimide induced by the polarized UV irradiation. The direction of the LC orientation could be changed by controlling the photoreaction of the polyimides using the appropriate UV filter for the polarized UV irradiation.

Effect of Plasticization of Poly(Vinyl Cinnamate) on Liquid Crystal Orientation Stability

A cinnamate group is a well-known compound group used in the dimerization reaction by ultraviolet irradiation, and cinnamate polymers are studied as photoalignment materials. In this study, the radical reaction of cinnamate side groups attached to a flexible polymer backbone is considered feasible using thermal energy. To induce the thermal reaction of cinnamate side groups, we modified the flexibility of poly(vinyl cinnamate) by introducing a plasticizer into the polymers and investigated the thermal reaction behavior of cinnamate side groups. The plasticization of poly(vinyl cinnamate) makes the induction of the thermal reaction of cinnamate side groups easier than that of unmodified poly(vinyl cinnamate). The thermal reaction of cinnamate side groups is closely related to the enhancement of the thermal stability of the liquid crystal orientation of polymer films with polarized UV irradiation.

P‐171: Effect of Plasticization of Poly(Vinyl Cinnamate) on Liquid Crystal Orientation Stability

A cinnamate group is a well-known compound group used in the dimerization reaction by ultraviolet irradiation, and cinnamate polymers are studied as photoalignment materials. In this study, the radical reaction of cinnamate side groups attached to a flexible polymer backbone is considered feasible using thermal energy. To induce the thermal reaction of cinnamate side groups, we modified the flexibility of poly(vinyl cinnamate) by introducing a plasticizer into the polymers and investigated the thermal reaction behavior of cinnamate side groups. The plasticization of poly(vinyl cinnamate) makes the induction of the thermal reaction of cinnamate side groups easier than that of unmodified poly(vinyl cinnamate). The thermal reaction of cinnamate side groups is closely related to the enhancement of the thermal stability of the liquid crystal orientation of polymer films with polarized UV irradiation.