Synthesis of low-cost, rubbery amphiphilic comb-like copolymers and their use in the templated synthesis of mesoporous TiO₂ films for solid-state dye-sensitized solar cells

Low-cost, rubbery amphiphilic comb-like copolymers consisting of hydrophobic poly(lauryl methacrylate) (PLMA) and hydrophilic poly(oxyethylene methacrylate) (POEM) were synthesized via one-step free radical polymerization. The synthesis of PLMA-POEM copolymers was confirmed using Fourier transform infra-red spectroscopy (FT-IR), ¹H-nuclear magnetic resonance ( ¹H-NMR) and gel permeation spectroscopy (GPC). The PLMA-POEM copolymers were used as a structure-directing agent for the formation of anatase mesoporous TiO₂ films. Careful adjustment of the precursor and polymer molecular weight (MW) was made to systematically vary the TiO ₂ structure and its effect on the performances of solid-state dye-sensitized solar cells (ssDSSCs). The use of a low MW polymer resulted in a worm-like structure with smaller pores, whereas an aggregated honeycomb-like structure with bimodal pores was obtained for the high MW system, as characterized by scanning electron microscopy (SEM), grazing incidence small-angle X-ray scattering (GI-SAXS) and N₂ adsorption-desorption measurement. An efficiency of 4.2% was obtained at 100 mW cm^-2 when using 2 μm-thick TiO₂ film prepared with a high MW copolymer. The higher efficiency was due to better pore filling of the solid electrolyte and improved light scattering properties. By using a layer-by-layer method, the efficiency was further improved to 5.0% at 7 μm thickness, which was greater than that of commercially available paste (3.9%).