ABSTRACT
So far, various ZnO nanostructures (e.g., nanoparticle, nanowire, nanorod, and nanosheet) have been investigated for DSSCs.6, 12, 17-20 A dense network of ZnO nanowires/nanorods should be favorable for electron collection because the nanowire morphology provides more direct conduction paths for electrons to transport from the point of injection to the collection electrode. However, as reported to date, the PCE is still low for DSSCs based on up-standing and highly ordered ZnO nanowires19-22 as compared to TiO2-based DSSCs where a PCE larger than 10% has been achieved.8-10 Recently, using hydrothermal method, Law et al.22 increased the aspect ratio of ZnO-nanowire to ~125 with polyethylenimine to hinder the lateral growth of the nanowires in solution. However, the device performances based on this film is still low with a low fill factor (FF, ~0.38) and low PCE (1.5%). As a photoanode, besides the electronic properties, the morphology of ZnO-nanostructure film plays a very important role in enhancing dye-loading and light-harvesting.
