Anode resistance reduction of dye-sensitized solar cells using graphene for efficiency improvement

In this study, electrochemical impedance spectroscopy of two types of photoanodes made up of TiO2 and graphene-TiO2 (with 6 wt% of graphene) composite are investigated in the dye-sensitized solar cells. In the first experiment, a 7-mu m thickness of TiO2 was used as a photoanode. Therefore, the short circuit current (SCC), open circuit voltage (OCV), and efficiency were obtained equal to 6.6 mA, 650 mV, and 3.4%, respectively. Also, the electron lifetime of this experiment in the anode section was obtained 13.2 ms. In the second experiment, graphene-TiO2 composite with 7-mu m thickness was used as a photoanode. Graphene, due to its small energy gap (approximately 0.1 ev), is an appropriate material to absorb more photons. Therefore, more electrons participate in generating SCC. So because of low impedance and high carrier mobility of graphene, electrons can move toward the fluorine-doped tin oxide easily, thus avoiding the recombination of electrons with highest occupied molecular orbital holes, resulting in improved efficiency of about 6.97%. The SCC, OCV, and electron lifetime obtained from the second experiment were obtained equal to 16.29 mA, and 690 mV, and 31 ms, respectively.