Mesoporous TiO(2) Bragg Stack Templated by Graft Copolymer for Dye-sensitized Solar Cells

Organized mesoporous TiO(2) Bragg stacks (om-TiO(2) BS) consisting of alternating high and low refractive index organized mesoporous TiO(2) (om-TiO(2)) films were prepared to enhance dye loading, light harvesting, electron transport, and electrolyte pore-infiltration in dye-sensitized solar cells (DSSCs). The om-TiO(2) films were synthesized via a sol-gel reaction using amphiphilic graft copolymers consisting of poly(vinyl chloride) backbones and poly(oxyethylene methacrylate) side chains, i.e., PVC-g-POEM as templates. To generate high and low index films, the refractive index of om-TiO(2) film was tuned by controlling the grafting ratio of PVC-g-POEM via atomic transfer radical polymerization (ATRP). A polymerized ionic liquid (PIL)-based DSSC fabricated with a 1.2-μm-thick om-TiO(2) BS-based photoanode exhibited an efficiency of 4.3%, which is much higher than that of conventional DSSCs with a nanocrystalline TiO(2) layer (nc-TiO(2) layer) (1.7%). A PIL-based DSSC with a heterostructured photoanode consisting of 400-nm-thick organized mesoporous TiO(2) interfacial (om-TiO(2) IF) layer, 7-μm-thick nc-TiO(2), and 1.2-μm-thick om-TiO(2) BS as the bottom, middle and top layers, respectively, exhibited an excellent efficiency of 7.5%, which is much higher than that of nanocrystaline TiO(2) photoanode (3.5%).