Photoelectrochemical studies of oriented nanorod thin films of hematite

Thin films consisting of nanorods of hematite (alpha-Fe2O3) with controlled orientation onto transparent conductive glass substrates have been tested as photoelectrochemical cells. These films allow a more efficient transport and collection of photogenerated electrons through a designed path compared to films constituted of sintered spherical particles. Experiments have been carried out taking into account the effect of morphology, orientation, film thickness, electrolyte composition, and dye sensitization. The results from a three-electrode system, with 0.1 M KI in water (pH 6.8) as electrolyte, illuminated either through the electrolyte/electrode interface or through the substrate (F:SnO2)/electrode interface, show an improvement of the IPCE (incident photon-to-current conversion efficiency) of 100 and 7 times, respectively, compared to work done earlier on thin films with spherical particles [U. Bjorksten, J. Moser, and M. Gratzel, Chem. Mater., 6, 858 (1994)]. Increasing the pH in the electrolyte from 6.8 to 12.0 also increases the IPCE by a factor two. For a sandwich-type cell, with 0.5 M LiI and 0.5 mM I-2 in ethylene carbonate/propylene carbonate (50:50% by weight) electrolyte, the IPCE reaches 56% at 340 nm. (C) 2000 The Electrochemical Society. S0013-4651(99)08-082-9. All rights reserved.