Electron Transport in Dye-Sensitized Solar Cells Based on ZnO Nanotubes: Evidence for Highly Efficient Charge Collection and Exceptionally Rapid Dynamics

Dye-sensitized solar cells based on ordered arrays of polycrystalline ZnO nanotubes, 64 μm in length, are shown to exhibit efficient electron collection over the entire photoanode array length. Electrochemical impedance spectroscopy, open-circuit photovoltage decay analysis, and incident-photon-to-current efficiency spectra are used to quantify charge transport and lifetimes. Despite the relatively thick photoanode, the charge extraction time is found to be faster than observed in traditional TiO2 nanoparticle photoanodes. If the extraction dynamics are interpreted as diffusive, effective electron diffusion coefficients of up to 0.4 cm2 s−1 are obtained, making these pseudo-1D photoanodes the fastest reported for an operating DSC to date. Rapid electron collection is of practical significance because it should enable alternative redox shuttles, which display relatively fast electron-interception dynamics, to be employed without significant loss of photocurrent.