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Conference: Bucharest University Faculty of Physics 2002 Meeting

Section: Electricity and Biophysics: Honorary Session Dedicated to Professors: Victor Gheorghe (Head of the Dept. 1972-1984) and Grigore Turcu

Title:

Light Energy Conversion by Chlorophyll a in Model Systems

Authors:

Laura Tugulea

Affiliation:

Faculty of Physics-University of Bucharest P.O.Box MG-11, Bucharest-Magurele, 76900 Romania

E-mail

Keywords:

Abstract:

At molecular level, the process of light energy conversion presents similarities in reaction centres and some model systems containing chlorophyll a. A comparative study was done on different types of devices using chlorophyll a in the form of a solid layer, coated on metal or semiconductor electrodes. Chlorophyll a coated electrodes were used to build up either photoelectrochemical cells or solid sandwich - type photovoltaic cells. Films of chlorophyll a (prepared from fresh spinach leaves) have been obtained by electrodeposition on electrodes. The electrodeposited chlorophyll a species presented a specific red absorption band at 740 nm. The size of these molecular aggregates, absorbing at 740 nm, is in the range of tens to hundred of nm. The chlorophyll a film thickness was in the range of 100 nm, as estimated from optical density at 740 nm. The electrodes (Me, SnO2, SnO2/TiO2) coated by chlorophyll a represented the front electrode in the photovoltaic cell or the working electrode in a typical electrochemical cell. The electrical features of the devices have been studied in dark and under illumination. Both dark electric features and the photocurrent action spectra of different photocells showed a strong dependence upon the particular interaction between the large molecular aggregates of chlorophyll a and the electrode surface. The consequences of the interaction chlorophyll a - electrode for interpreting the chlorophyll a behaviour in the charge separation under illumination are discussed. The nature of the semiconductor electrode, i.e. nanoparticulate, porous or uniform film, at the interface with chlorophyll a thin film proved to be the dominant factor in controlling the photoinduced electron transfer. A model for electron transport in nanocrystalline electrodes is proposed as a starting point for a more refined treatment. New insights for in vivo charge generation are also envisaged.