Characteristics of dye-sensitized solar cells based on the TiO2 nanotube/nanoparticle composite electrodes

The influence of TiO2 nanotubes on the charge collection efficiency and the dynamics of electron transport and recombination in dye-sensitized solar cells (DSCs) based on the TiO2 nanotube/nanoparticle composite films were investigated in this paper. Electrochemical impedance spectroscopy was employed to quantify the charge transfer resistance of DSCs. The different transport and recombination properties of DSCs were studied by frequency-resolved modulated photocurrent/photovoltage spectroscopies. It was shown that the electrons had a longer lifetime in the nanotubes and retarded recombination more significantly than in the nanoparticles. But with increasing the amount of nanotube, the electron pathway was extended seriously in these network structures resulting in increased recombination chances. In addition, the 5 wt% nanotube DSC had the highest charge collection efficiency among all the DSCs, which yielded a high photovoltaic conversion efficiency of 9.79% under simulated AM 1.5 sunlight (100 mW cm(-2)).