Low temperature synthesis of flower-like TiO2 nanospheres directly from block-graft copolymer precursors and their uses in quasi-solid-state dye-sensitized solar cells

We report a low temperature synthetic method for preparing flower-like TiO2 nanospheres (f-TiO2 NS) directly from an amphiphilic block-graft copolymer precursor. The copolymer, consisting of poly(ethylene glycol) titanium triisopropoxide (PEGTTIP) and polystyrene (PS), was synthesized via atom transfer radical polymerization (ATRP) and was characterized by Fourier transform infrared (FT-IR) spectroscopy. The copolymer was directly hydrolyzed at 90 °C for 6 h without any additives to generate rutile-phase f-TiO2 NS that were approximately 800 nm in size, as confirmed by field emission scanning electron microscopy (FE-SEM), energy-filtering transmission electron microscopy (EF-TEM) and X-ray diffraction (XRD). The energy conversion efficiency of quasi-solid-state dye-sensitized solar cells (qssDSSCs) fabricated with f-TiO2 NS (4.4% at 100 mW/cm2) as a scattering layer (SL) was greater than those without f-TiO2 NS (3.8% for 10 μm, 3.9% for 17 μm) and was quite comparable to cells with a commercial scattering layer (CSL). The improved efficiency is attributed to the increased dye loading and improved light scattering effect, as confirmed by incident photon-to-electron conversion efficiency (IPCE) measurements