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In this study, graphene/TiO2 composite films at different annealing temperatures from 450 to 650 °C acted as photoelectrode of dye-sensitized solar cell (DSSC). The graphene/TiO2 composite films were characterized by scanning electronic microscopy, X-ray diffractometer, and electrochemical impedance spectroscopy. The Nyquist plot is built to simulate the redox reaction of internal device at the heterojunction by an equivalent circuit model. It is useful to analyze the component structure and promote photovoltaic conversion efficiency of DSSC. According to the experiment results, the optimal annealing temperature of graphene/TiO2 composite film was 550 °C, where the open-circuit voltage was 0.74 ± 0.01 V, the short-circuit current density was 14.17 ± 0.32 mA/cm2, the fill factor was 51.00 ± 1.95%, and the photovoltaic conversion efficiency was 5.34 ± 0.12%.

Graphene/TiO2 composite films were deposited on fluorine-doped SnO2-coated conductive substrates by spin coating acting as photoelectrodes of dye-sensitized solar cells. The graphene/TiO2 composite films were characterized by scanning electronic microscopy, an X-ray diffractometer, a UV–visible spectrometer, and electrochemical impedance spectroscopy. Nyquist plots showed the decrease of impedance, in which electron transport rate was promoted. The photovoltaic properties showed that the incorporation of graphene could increase the short-circuit current density and photoelectric conversion efficiency. However, an excessive incorporation of graphene led to the enhancement of charge recombination and the reduction of photoelectric conversion efficiency. The graphene/TiO2 composite film with 1.5-mL graphene oxide solution obtained the optimal photoelectric conversion efficiency of 5.26%.