Research on the effect of different sizes of ZnO nanorods on the efficiency of TiO2-based dye-sensitized solar cells

TiO2-based dye-sensitized solar cells doped with different sizes of ZnO nanorods were fabricated and studied by photoelectrochemical measurements. The results show that the solar conversion efficiency of the dyesensitized solar cells after the addition of ZnO nanorods (1 wt %) was increased by about 15% compared to that without ZnO nanorods. The effect of different sizes of ZnO nanorods on the charge carrier transport properties has been studied in the composite semiconductor film by means of a transient photovoltage technique. The result indicates that the carrier diffuse rate in the cis-di(isothiocyanato)-bis(4,4'-dicarboxy-2,2'-bipyridine)ruthenium(II)-sensitized TiO2/ZnO film electrode was about 1 to 3 orders of magnitude faster than that in the TiO2 electrode. The cyclic voltammograms suggest that the conduction band edge shifts toward the vacuum level after the addition of ZnO nanorods in working electrodes, which may be the main, cause of the enhancement of the open-circuit photovoltage (V-oc). The experimental results indicate that the addition of ZnO nanorods can improve charge carrier transport, decrease recombination, enhance V-oc, and increase the efficiency of energy conversion.