Self-aggregates of synthetic zinc chlorins as the photosensitizer on carbon paste electrodes for a novel solar cell

To investigate a dye-based solar cell, a naturally occurring chlorophyll an alogue (chlorin 1) modified electrode was prepared. Synthetic zinc chlorin 1 easily self-aggregated to form supramolecules (1)(n) in non-polar organic solvents as well as in the thin film. The photocurrent of the electrode mo dified with self-aggregated chlorin (1)(n) (CE1) was measured in the range from - 300 to 300 mV (vs. Ag \ Ag+) by irradiation with > 510 nm light. Bel ow 100 mV of the bias potential, cathodic photocurrents of CE1 were observe d in an aqueous solution of 0.1 M 2-(N-morpholino)ethanesulfonic acid + 0.1 M Na2SO4 at pH 6.7. The photocurrent action spectrum of CE1 was similar to the visible absorption spectrum of (1), on a Pyrex plate, indicating that the photoexcited slate of zinc chlorin aggregates (1)(n)* played a role as a photosensitizer on CE1 with a wide band of longer wavelength light. An ox ygen molecule dissolved in an aqueous solution was an electron acceptor; el ectron transfer from (1)(n)* to O-2 at the interface between the carbon pas te electrode and the aqueous solution yielded the cathodic photocurrent. Th e quantum yield for CE1 was estimated to be 0.09% (730 nm). The value was l arger than the quantum yield for the carbon paste electrode modified with m onomeric zinc chlorin 3 (CE3), 0.01% (660 nm). These results indicate that self-aggregation of zinc chlorin (1)(n) made an efficient photosensitizer o f solar cells and utilized up to 800 nm light. (C) 2001 Elsevier Science B. V. All rights reserved.