Synthesis of Organized TiO₂ Electrodes Using Graft Copolymer and Their Applications to Dye-Sensitized Solar Cells

다국어 초록 (Multilingual Abstract)

The morphology of mesoporous TiO₂ films plays an important role in the operation of a DSSC. For example, the energy conversion efficiency of DSSCs with well-organized mesoporous TiO₂ films is much higher than those with traditional films possessing a random morphology. In previous research, well-organized mesoporous TiO₂ films have mainly been synthesized using an amphiphilic block copolymer, e.g., a poly(ethylene oxide) (PEO)-based template. A graft copolymer is more attractive than a block copolymer due to its low cost and the ease with which it can be synthesized. In this work, we provide the first report on the successful synthesis of well-organized mesoporous TiO₂ films templated by an organized graft copolymer as a structure directing agent. Well-organized mesoporous TiO₂ films with excellent channel connectivities were developed via the sol gel processusing an organized PVC-g-POEM graft copolymer synthesized by one-pot ATRP. The careful adjustment of copolymer composition and solvent affinity using a THF/H₂O/HCl mixture was used to systematically vary the material structure. The influence of the material structure on solar cell performance was then investigated. A solid-state DSSC employing both the graft copolymer templated organized 700 nm-thick TiO₂ films and graft copolymer electrolytes exhibited a solar conversion efficiency of 2.2% at 100 mW/cm². This value was approximately two-fold higher than that attained from a DSSC employing a random mesoporous TiO₂ film. The solar cell performance was maximized at 4.6% when the film thickness was increased to 2.5{mu}m. We believe that this graft copolymer-directed approach introduces a new and simple route toward the synthesis of well-organized metal oxide films as an alternative to a conventional block copolymer-based template.