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%).
Bibliographical noteFunding Information:
This work was supported by a National Research Foundation (NRF) grant and funded by the Korean government (MEST) through the Active Polymer Center for Pattern Integration (2007-0056091) and the Core Research Program (2012R1A2A2A02011268). D. L. acknowledges the support of NSF CBET-1234993 and NSF DMR-1055594.
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