Enhancement of carrier-collection by electrospun Nb-doped TiO$$_2$$ nanofiber-network in photoelectrode of dye-sensitized solar cells

Abstract

Conductive nanofiber(NF)-network in nano scale is expected to act as a collector of excited carriers in a medium with short diffusion length of carriers. For the effective usage of conductive NF-network in mesoporous media, we tried to actualize the composite structure of electrospun NF-network of Nb-doped TiO $$_2$$ (TNO) in a mesoporous TiO $$_2$$ layer keeping the network and its direct connection to conductive substrate. The effects of inserted NF-network with different mesh size were examined for the performance of dye-sensitized solar cells. By the insertion of NF-network, the power conversion efficiency $$\eta$$ was increased by 29.3% resulting from the increase of the short circuit current density $$J_\text{sc}$$ by 31.3%. From the time-resolved spectra of photovoltage and photocurrent, and electrochemical impedance spectra, it was found that photoelectrodes with NF-network had long lifetime of the electrons $$\tau _\text{e}$$ , small recombination rate of electrons $$k_\text{eff}$$ , and large steady state electron density $$n_\text{s}$$ . The enhancement of photocurrent and the external quantum efficiency also shows that TNO NF-network acts as a good carrier collector with the low leakage rate of photoexcited carriers.