Enhancement of carrier mobility by electrospun nanofibers of Nb-doped TiO2 in dye sensitized solar cells

The electrospun nanofibers (ES-NFs) of TiO2 and Nb doped TiO2 (NTO) were added to the TiO2 mesoporous layer in the photoelectrode of dye sensitized solar cells (DSCs) as a conductive agent, and their effects to the carrier mobility and photovoltaic characteristics were examined. The nonwoven sheets of TiO2-NFs and NTO-NFs of which diameter was about 120 nm were prepared, and their fragments were mixed into the TiO2 mesoporous layer. By mixing ES-NFs of TiO2 and NTO, the short-circuit current density Jsc was increased by 6% and 8%, respectively. From the time-transient spectra of photocurrent excited by a pulse laser irradiation, the diffusion velocity of photoexcited carriers in the TiO2 mesoporous layer was found to be increased by 70% and 165%, while the amount of mixed NFs was small, ∼10 vol%. Furthermore, the enhancement of photocurrent due to the band bending was also observed at the interface of TiO2/NTO. The electrochemical impedance spectra (EIS) showed that ohmic resistance of the photoelectrode was reduced by 4% and 15% by the mixture. Thus, it was found that ES-NFs of NTO are a good conductive agent for the accumulation of photoexcited carriers in dye/TiO2 nanoparticles.