Photocurrent generated on a carotenoid-sensitized TiO2 nanocrystalline mesoporous electrode

Photocurrent was observed upon monochromatic illumination of an ITO electrode coated with a TiO(2) nanocrystalline mesoporous membrane with carotenoid 8'-apo-beta-caroten-8'-oic acid (ACOA) deposited as a sensitizer (illuminated area 0.25 cm(2)) and immersed in an aqueous 10 mM hydroquinone (H(2)Q), 0.1 M NaH(2)PO(4) solution (pH = 7.4) purged with argon, using a platinum flag counter electrode (area 3.3 cm(2)) and a SCE reference electrode. The carotenoid-sensitized short-circuit photocurrent reached 4.6 mu A/cm(2) upon a 40 mu W/cm(2) incident light beam at 426 nm, with an IPCE (%, incident monochromatic photon-to-photocurrent conversion efficiency) as high as 34%. The short-circuit photocurrent was stable during 1 h of continuous illumination with only a 10% decrease. An open-circuit voltage of 0.15 V was obtained (upon 426 nm, 40 mu W/cm(2) illumination) which remained at a constant value for hours. The observed open-circuit voltage is close to the theoretical value (0.22 V) expected in such a system. The action spectrum resembled the absorption spectrum of ACOA bound on the TiO(2) membrane with a maximum near 426 nm. No decay of the ACOA on the TiO(2) surface was observed after 12 h, presumably because of rapid regeneration of ACOA from ACOA(.+) at the surface by electron transfer from H(2)Q. (C)2000 Elsevier Science S.A. All rights reserved.