Enhanced performance of a flexible dye-sensitized solar cell with a composite semiconductor film of ZnO nanorods and ZnO nanoparticles

A composite thin film of only 6 mu m, consisting of a first layer of ZnO nanorods (ZNRs) and a second layer of ZnO nanoparticles (ZNPs), was deposited on a flexible Ti foil. The structures and morphologies of the films of ZNRs, ZNPs, and their composite (hereafter ZNRs/ZNPs) were studied by X-ray diffraction (XRD) patterns, scanning electron microscopic (SEM) and transmission electron microscopy (TEM) images. The Ti foil with the composite film was used as the photoanode of a flexible dye-sensitized solar cell (DSSC); an indium doped tin oxide/polyethylene naphthalate (ITO/PEN) substrate with a thin layer of platinum was used as the counter electrode. A power conversion efficiency (eta) of 2.19% was achieved for the DSSC with ZNRs/ZNPs, through back-illumination, which is higher than that of the cell with only ZNPs (1.80%); the DSSC with bare ZNRs showed a very poor efficiency of 0.90%. Explanations are substantiated by electrochemical impedance spectra (EIS), laser-induced photo-voltage transients, and incident photon-to-electron conversion efficiency (IPCE) curves. (C) 2011 Elsevier Ltd. All rights reserved.