Preparation of Ordered Mesoporous Alumina-Doped Titania Films with High Thermal Stability and Their Application to High-Speed Passive-Matrix Electrochromic Displays

• Published in: Chemistry : a European journal 2013-08, Vol.19 (33), p.10958-10964
• Main Authors: Jiang , Xiangfen, Bastakoti, Bishnu Prasad, Weng, Wu, Higuchi, Tetsuya, Oveisi , Hamid, Suzuki , Norihiro, Chen, Wei-Jung, Huang, Yu-Tzu, Yamauchi , Yusuke
• Format: Article
• Language: English
• Subjects: Aluminum; Aluminum Oxide - chemistry; Calcination; Coloring Agents - chemistry; Crystallization; display technology; Displays; doping; Dyes; Electrochemical Techniques; electrochomism; Electrochromism; Electrodes; High speed; Hot Temperature; mesoporous materials; Poloxalene - chemistry; Porosity; Scattering, Small Angle; thin films; Titanium - chemistry; Titanium dioxide; X-Ray Diffraction
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201300737

Ordered mesoporous alumina‐doped titania thin films with anatase crystalline structure were prepared by using triblock copolymer Pluronic P123 as structure‐directing agent. Uniform Al doping was realized by using aluminum isopropoxide as a dopant source which can be hydrolyzed together with titanium tetraisopropoxide. Aluminum doping into the titania framework can prevent rapid crystallization to the anatase phase, thereby drastically increasing thermal stability. With increasing Al content, the crystallization temperatures tend to increase gradually. Even when the Al content doped into the framework was increased to 15 mol %, a well‐ordered mesoporous structure was obtained, and the mesostructural ordering was still maintained after calcination at 550 °C. During the calcination process, large uniaxial shrinkage occurred along the direction perpendicular to the substrate with retention of the horizontal mesoscale periodicity, whereby vertically oriented nanopillars were formed in the film. The resulting vertical porosity was successfully exploited to fabricate a high‐speed and high‐quality passive‐matrix electrochromic display by using a leuco dye. The vertical nanospace in the films can effectively prevent drifting of the leuco dye. Vertical porosity of mesoporous alumina‐doped titania thin films, generated by uniaxial shrinkage along the direction perpendicular to the substrate during calcination, was exploited to fabricate a high‐speed, high‐quality passive‐matrix electrochromic display by using a leuco dye. In the imaging process, the leuco dye is transformed into a colored dye on the surface of the working electrode when an electric current is applied. The mesoporous working electrode and nonmesoporous counterelectrode cross each other orthogonally, and the points of intersection of the electrodes are colorable positions (see figure).