Determination of the light-induced degradation rate of the solar cell sensitizer N719 on TiO2 nanocrystalline particles

The oxidative degradation 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 solutions of N719-dyed TiO2 particles in acetonitrile were irradiated with 532-nm monochromatic light, and the sum of the quantum yields for the oxidative degradation products [RuL2(CN)2], [RuL2(NCS)(CN)], and [RuL2(NCS)(ACN)], deg , were obtained at eight different light intensities in the range of 0.1–16.30 mW/cm2 by LC-UV-MS. The deg values decreased from 3.3 × 10–3 to 2 × 10–4 in the applied intensity range. By using the relation kdeg = deg × kback and back electron transfer reaction rates, kback, obtained using photoinduced absorption spectroscopy, it was possible to calculate an average value for the oxidative degradation rate of N719 dye attached to TiO2 particles, kdeg = 4 × 10–2 s–1. The stability of N719 dye during solar cell operation was discussed based on this number, and on values of the electron transfer rate between [Ru(III) L2(NCS) 2] and iodide that are available in the literature.