Dye-sensitized solar cells based on TiO2 particulate gels: Impact of gel formation mechanism on photovoltaic performance

In this work the influence of different particulate gels on morphology and photoelectric performance of TiO2 dye-sensitized solar cells (DSCs) is studied. Two coagulant and flocculant agents are used to convert a TiO2 particulate sol into the gels using double layer compression and charge neutralization mechanisms. One more TiO2 particulate gel is also prepared by changing the pH of the sol using acid: alkoxide molar ratio higher than the critical ratio to obtain an unstable sol. Based on X-ray diffraction (XRD) analysis, the films contain primary nanoparticles with average crystallite size of 13-15 nm. Field emission scanning electron microscopy (FE-SEM) images show uniform, nanostructured and porous microstructure of the films. For acid- coagulated condition the deposited films show large spherical particles (140-260 nm) containing small nanoparticles, while for base-coagulated condition the films contain 20-40 nm nanoparticles. Photovoltaic measurements reveal that DSCs made of basic particulate gel show higher cell efficiency (i.e., 7.68%) than those prepared by acidic particulate gel (i.e., 6.02% and 7.08%). Such enhancement of efficiency is attributed to the small particle size of the films leading to large surface area for high dye adsorption and good interconnectivity of the nanoparticles for electron transport improvement.