Construction of nanocrystalline film on nanowire array via swelling electrospun polyvinylpyrrolidone-hosted nanofibers for use in dye-sensitized solar cells.

A 74% enrichment of the efficiency of ZnO nanowire (NW) dye-sensitized solar cells (DSSCs) is achieved by the addition of a novel light-scattering nanocrystalline film (nanofilm). The 100 nm thick nanofilm is derived from the polyvinylpyrrolidone-hosted SnO(2)/ZnO nanofibers electrospun on the top of ZnO NW arrays via methanol vapor treatment followed by high-temperature calcination. Structural characterizations show that the film is composed of SnO(2) and ZnO nanocrystals with a diameter of ∼10 nm. Short-circuit current, open-circuit voltage, and fill factor of the nanofilm/ZnO NW DSSCs are all superior to those of the ZnO NW DSSCs. The mechanism of photocurrent enhancement in the nanofilm/ZnO NW DSSCs has been investigated using optical modulation spectroscopy. Intensity modulation photocurrent spectroscopy (IMPS) measurements reveal that the dye-sensitized nanofilm does not contribute significant photocurrent in the nanofilm/ZnO NW DSSCs. The significant enhancement of the efficiency of the ZnO NW DSSCs is achieved by reflecting unabsorbed photons back into the NW anode using the novel light-scattering layer of nanofilm.