Photogeneration of charges in microcrystalline chlorophyll a

Hassan Kassi, Saïd Barazzouk, Marc Brullemans, Roger M. Leblanc, Surat Hotchandani

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


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, rc, from S/I. From the temperature dependence of photogeneration, the initial separation, r 0, of photogenerated electron-hole has been evaluated, and has a value of 1.24 nm. This smaller r0 compared to rc 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.

Original languageEnglish (US)
Pages (from-to)5345-5348
Number of pages4
JournalThin Solid Films
Issue number18
StatePublished - Jul 1 2010


  • Electric field
  • Microcrystalline chlorophyll a
  • Onsager approach
  • Photocarrier generation
  • Time-of-flight technique

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Materials Chemistry
  • Metals and Alloys
  • Surfaces, Coatings and Films
  • Surfaces and Interfaces


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