Photocurrent generated on a carotenoid-sensitized TiO2 nanocrystalline mesoporous electrode

Photocurrent was observed upon monochromatic illumination of an ITO electrode coated with a TiO2 nanocrystalline mesoporous membrane with carotenoid 8′-apo-b-caroten-8′-oic acid (ACOA) deposited as a sensitizer (illuminated area 0.25 cm2) and immersed in an aqueous 10 mM hydroquinone (H2Q), 0.1 M NaH2PO4 solution (pH = 7.4) purged with argon, using a platinum flag counter electrode (area 3.3 cm2) and a SCE reference electrode. The carotenoid-sensitized short-circuit photocurrent reached 4.6 mA/cm2 upon a 40 mW/cm2 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 mW/cm2 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 TiO2 membrane with a maximum near 426 nm. No decay of the ACOA on the TiO2 surface was observed after 12 h, presumably because of rapid regeneration of ACOA from ACOA•+ at the surface by electron transfer from H2Q. ©2000 Elsevier Science S.A. All rights reserved.