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 J_SC of 17.98 mA/cm², V_OC 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.