Micron-thick, worm-like, organized TiO₂ films prepared using polystyrene-b-poly(2-vinyl pyridine) block copolymer and preformed TiO ₂ for solid-state dye-sensitized solar cells

Crack-free, micron-thick, worm-like mesoporous TiO₂ films with an anatase phase, organized pores, and good interconnectivity were prepared by the self-assembly of anionically polymerized polystyrene-bpoly( 2-vinyl pyridine) (PS-b-P2VP) block copolymer and hydrophilically preformed TiO ₂ nanocrystals. The polymer concentration and polymer:TiO₂ ratio were carefully adjusted to systematically vary the TiO₂ structure and evaluate the effects on the performances of solid-state dye-sensitized solar cells (ssDSSCs). As evaluated by scanning electron microscopy (SEM), grazing incidence small-angle X-ray scattering (GISAXS), and N₂ adsorption-desorption measurements, the use of a higher polymer concentration (6 wt%) and a polymer:TiO₂ ratio of 1:2, referred to as P6T2, resulted in a worm-like structure with a large surface area and smaller mesopores, whereas an aggregated structure with bimodal pores was obtained with a polymer:TiO₂ ratio of 1:1. An efficiency of 4.0% was obtained at 100 mW/cm² when using a 2.8 μm thick P6T2 film as a photoanode in a ssDSSC, which is much greater than the efficiency of commercially available paste (2.3%) with a similar film thickness. The higher efficiency of the P6T2 cells is due to the improved current density, resulting from its larger surface area, well-organized pores, and good interconnectivity.