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 TiO2 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%).