Nanochannel morphology of polypyrrole-ZnO nanocomposites towards dye sensitized solar cell application

Polypyrrole (PPy)-zinc oxide (ZnO) nanocomposites (PZ1, PZ2 and PZ3) are prepared by polymerizing pyrrole (1.3 x 10(-6) mol) in the presence of various amounts of ZnO nanoparticles (NPs) (25, 100, 250 mg) in a lauric acid (LA)-cetyl trimethyl ammonium bromide (CTAB) coacervate gel template. PPy formed in the gel template has a nanorod morphology, but it gradually changes exhibiting an open nanotube (nanochannel) morphology in the PZ3 sample, although ZnO has a nanosphere morphology. PPy nanorod formation is attributed to the coalescence of PPy nanospheres and the nanochannel morphology of PZ3 is attributed to the restricted growth of PPy in the gel pores due to the steric hindrance of the ZnO NPs. The ZnO NPs have a hexagonal wurtzite structure, which is also retained in the PZ samples. FTIR and UV-vis spectra indicate the presence of an interaction between the PPy and ZnO NPs. The ZnO NPs exhibit only UV band gap fluorescence at 390 nm, and in the PZ3 sample there is a reduction in the peak intensity with a red shift of 8 nm, supporting a strong electronic interaction between PPy and the ZnO NPs. The dc conductivity of the PZ3 composite is the highest (7.9 x 10(-5) S cm(-1)) among the other composites, and also among the components. A dye sensitized solar cell (DSC) fabricated with the PZ3 composite using N719 dye as the photosensitizer has the cell characteristics V-oc = 0.56 V, J(sc) = 8.54 mA cm(-2) and the fill factor (FF) = 0.53 giving an overall power conversion efficiency eta = 2.53%, which is higher than those fabricated with pure ZnO NPs (eta = 1.87%) and the PZ1 (1.98%) samples.