Tailoring of nanoporous TiO2 spheres with 100–200 nm sizes for efficient dye-sensitized solar cells

Highly porous and monodispersed TiO2 spheres (SPs) with diameters in the range of 100–200 nm, notably smaller than the conventional SPs reported thus far, were selectively controlled, and found to be an outstanding building block for the mesoporous TiO2 layer in dye-sensitized solar cells (DSCs). The prepared TiO2 films employing these SPs are highly transparent, and the fabricated DSCs exhibit significantly enhanced photovoltaic performances. Particularly, the 100 nm-sized TiO2 SP (SP100) provides a photovoltaic conversion efficiency (PCE) of 10.66% with a JSC of 17.98 mA/cm2, VOC of 808 mV, and FF of 0.734, which is higher than the PCE of DSCs with the typical 20 nm-sized TiO2 nanoparticle (NP20) or conventional 250 nm-sized SP (SP250). Transient photoelectron spectroscopic analyses revealed that both the electron diffusion coefficient and electron lifetime of the TiO2 layer increase as the size of the SPs decreases. The tiny TiO2 SPs prepared in this work offer distinct advantages in electron transport as well as dye-soaking and electrolyte diffusion.