Hybrid solar cells based on blends of poly(3-hexylthiophene) and surface dye-modified, ultrathin linear- and branched-TiO2 nanorods

We report on a comparative study of hybrid solar cells based on blends of poly(3-hexylthiophene) (P3HT) and TiO2 nanorods. Two types of ultrathin TiO2 nanorods, linear and branched, have been synthesized for the first time, and surface modified with different dyes before blending with P3HT. Using pristine P3HT as a reference, the short-circuit current and energy conversion efficiency of poly(3-hexylthiophene)/pyridine-HgBrRed-modified branched-TiO2 solar cells were increased by over an order of magnitude, which were also 2–3 times those of the corresponding linear-TiO2 cells. Our results indicate that the branching and the surface dye modification of TiO2 nanorods could effectively facilitate charge transport in the nanostructured network and exciton dissociation at the inorganic/organic interfaces. Thermal treatment of the blend films was found to further increase the efficiency up to 0.16%.