Temperature-dependent infrared spectrum of (Bu4N)2[Ru(dcbpyH)2-(NCS)2] on nanocrystalline TiO2 surfaces

The thermal degradation behavior of the self-assembled thin films of (Bu4N)2[Ru(dcbpyH)2-(NCS)2] (N719) anchoring on TiO2 surfaces via its carboxylate group has been studied using temperature-dependent diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Our analysis indicate that the decomposition temperature of N719 appeared to be at ≈270 °C on TiO2 surfaces, whereas such decompositions occurred at temperatures higher than ≈340 °C in their solid states as line with the thermal analysis data. This change was also found to be irreversible, if heated above 100 °C on TiO2 surfaces. Our 2D correlation spectroscopy and principal component analysis (PCA) applied to the temperature-dependent DRIFT spectra supported that the thermal degradation mechanism for N719 should differ in its solid state and on TiO2 powder surfaces. The NCS stretching vibrational intensities of the neat N719 vibrations were found to shift from 2102 to 1975 cm−1 increase with increase in temperatures, whereas similar vibration changes from 2095 to 2008 cm−1 were observed for N719 attached to TiO2. Referring from the open-circuit potential, short-circuit, fill factor, and efficiency measurements for the N719 dye-loaded photoelectrodes depending on temperature, the NCS stretching band at ∼2008 cm−1 on TiO2 surfaces appeared to be correlated with the thermal degradation of the DSSCs.