Syntheses of size-varied nanorods TiO₂ and blending effects on efficiency for dye-sensitized solar cells

A series of one-dimensional anatase nanorods TiO₂ with various lengths and aspect ratios are synthesized. The smallest rods TiO₂ (EOA) with a length of 20-40 nm and a width of about 5 nm possess extremely high surface area (151.5 m² g^-1) compared to P25 (56.4 m ² g^-1) and the largest rods TiO₂ (TMA-L) with a length of 800 nm and a width of about 200 nm result in very low transmittance. The EOA show the lower R_w (charge transport resistance) and higher R_k (charge recombination resistance) than the P25. It indicates that the one-dimensional TiO₂ structure lowers the charge transport resistance by decreasing grain boundary and stretching grown structure with the specified directionality, and increases recombination reaction due to reducing the surface defects. A higher light-to-electricity conversion yield of 5.61% is achieved by applying the EOA as compared with P25 (5.08%). The TMA-L coat on the EOA film to form double-layer films enhances the efficiency from 5.61 to 5.84%, and the scattering layer of the blending of EOA and TMA-L coated on the EOA film raises the efficiency to 6.08%.