Electrospun coaxial titanium dioxide/carbon nanofibers for use in anodes of dye-sensitized solar cells

TiO₂/carbon coaxial-structured nanofibers (TCNFs), applied as photoanodes in dye-sensitized solar cells (DSSCs), were fabricated by coaxial electrospinning. The precursor of the TCNFs was electrospun using polyacrylonitrile in the core and a blend of titanium isopropoxide and polyvinylpyrrolidone in the shell. After calcination at 500 °C for 2 h in air and subsequent carbonization at 1000 °C for 2 h in nitrogen, the TCNFs were formed with nanocrystalline TiO₂ in the shell layer and carbon in the core. The structure and morphology of the TCNFs were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The photovoltaic properties of the TCNF photoelectrode-based DSSCs were investigated by determining current density-voltage (J-V) curves, incident photon-to-current conversion efficiency (IPCE), and electrochemical impedance spectroscopy (EIS). The power conversion efficiency (PCE) of the TCNF photoelectrode-based DSSC was 7.5%, higher than those of DSSCs with TiO ₂ nanofiber (TNF)- and TiO₂ nanoparticle (TNP)-based photoelectrodes. An increase in the electron transport and suppression of charge recombination were found with the carbon core and nanocrystalline TiO ₂ shell configuration of the TCNFs.