Effect of Carbon Modification on the Electrical, Structural, and Optical Properties ofTiO2Electrodes and Their Performance in Labscale Dye-Sensitized Solar Cells

Abstract

Carbon-modified titanium dioxide nanoparticles (C:TiO2NPs) have been synthesized by ultrasonic nebulizer spray pyrolysis (USP) and pneumatic spray pyrolysis (PSP) techniques. HRTEM on the NPs shows difference in lattice spacing in the NP structures prepared by the two methods—2.02 Å for the USP NPs and an average of 3.74 Å for the PSP NPs. The most probable particle sizes are 3.11 nm and 5.5 nm, respectively. Raman spectroscopy supported by FTIR confirms the TiO2polymorph to be anatase with the intense phonon frequency at 153 cm−1blue-shifted from 141 cm−1ascribed to both carbon doping and particle size. A modified phonon confinement model for nanoparticles has been used to extract phonon dispersion and other parameters for anatase for the first time. Electronic measurements show “negative conductance” at some critical bias voltage, which is characteristic ofn-type conductivity in the carbon-doped TiO2NPs as confirmed by the calculated areas under theI-Vcurves, a property suited for solar cell applications. Practical solar cells built from carbon-doped TiO2electrodes show up to 1.5 times improvement in efficiency compared to pure TiO2electrodes of similar construction.