Determination of the Light-Induced Degradation Rate of the Solar Cell Sensitizer N719 on TiO2 Nanocrystalline Particles

The oxidative degrdn. rate, kdeg, of the solar cell dye (Bu4N+)2[Ru(dcbpyH)2(NCS)2]2-, referred to as N719 or [RuL2(NCS)2], was obtained by applying a simple model system. Colloidal solns. of N719-dyed TiO2 particles in acetonitrile were irradiated with 532-nm monochromatic light, and the sum of the quantum yields for the oxidative degrdn. products [RuL2(CN)2], [RuL2(NCS)(CN)], and [RuL2(NCS)(ACN)], Φdeg, was obtained at eight different light intensities at 0.1-16.30 mW/cm2 by LC-UV-MS. The Φdeg values decreased from 3.3 × 10-3 to 2.0 × 10-4 in the applied intensity range. By using the relation kdeg = Φdegkback and back electron-transfer reaction rates, kback, obtained with photoinduced absorption spectroscopy, it was possible to calc. an av. value for the oxidative degrdn. rate of N719 dye attached to TiO2 particles, kdeg = 4.0 × 10-2 s-1. The stability of N719 dye during solar cell operation was discussed based on this no., and on values of the electron-transfer rate between [Ru(III)L2(NCS) 2] and iodide ion that are available in the literature.