One-step fabrication of crack-free, hierarchically-ordered TiO₂ films via self-assembly of polystyrene bead and preformed TiO₂

Crack-free, hierarchically-ordered TiO₂ films were prepared via one-step co-assembly of a 400-nm polystyrene bead and hydrophilically preformed TiO₂. Large volume loss of titanium(IV) bis(ammonium lactato) dihydroxide, a commonly used precursor, led to substantial crack formation of the film. However, the use of preformed TiO₂ resulted in less cracked films with higher thickness and a meso/macroscopic scale hierarchical structure. This is because the preformed TiO₂ particles electrostatically assembled onto the polystyrene bead surface, as confirmed by scanning electron microscope and a zeta potential analyzer. When these structures were implemented as photoanodes in quasi-solid-state dye-sensitized solar cells using a nanogel electrolyte, the efficiency of the preformed TiO₂-based cell was 1.8-fold greater than that of a titanium(IV) bis(ammonium lactato) dihydroxide-based cell, indicating the importance of the precursor. Upon fabrication of solid-state dye-sensitized solar cells using a high molecular weight polymer and the TiCl₄-treated TiO₂ film, the efficiency was much greater than that of less-organized, nanoparticle-based cells fabricated with commercially available paste (Dyesol, 18NR-T). This indicates the increased effectiveness of the film in solid-state high molecular weight systems.