Journal
THIN SOLID FILMS
Volume 518, Issue 18, Pages 5345-5348Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.tsf.2010.04.002
Keywords
Microcrystalline chlorophyll a; Photocarrier generation; Electric field; Time-of-flight technique; Onsager approach
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Funding
- Natural Sciences and Engineering Research Council of Canada
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The electric-field and temperature dependence of hole photogeneration in chlorophyll a (Chla) have been analyzed in terms of electric-field assisted thermal dissociation of charge pairs based on Onsager theory. An excellent agreement between the experimental and theoretical values of the slope-to-intercept ratio, S/I, for the plot of photogeneration efficiency vs. electric field at low field strengths provides a proof for the applicability of the Onsager approach to the photogeneration of charges in Chla. A value of 19 nm has been obtained for Coulomb capture radius, r(c), from S/I. From the temperature dependence of photogeneration, the initial separation, r(o), of photogenerated electron-hole has been evaluated, and has a value of 1.24 nm. This smaller ro compared to r(c) leads to a feeble dissociation probability of electron-hole pairs into free carriers, and may, among other factors, explain the low power conversion efficiencies of Chla photovoltaic cells. (C) 2010 Elsevier B.V. All rights reserved.
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