We have investigated the thermal stability of the heteroleptic ruthenium complex C106 employed as a sensitizer in dye- sensitized solar cells. The C106 was adsorbed on TiO2 particles and exposed to 2 different iodide/triidode based redox electrolytes A and B at 80 ºC for up to 1500 hours in sealed glass ampules. Both electrolytes contain guanidiniumthiocyanate (GuNCS) and N-butylbenzimidazole (NBB) as additives. Electrolyte A: 1,3-dimethylimidazolium iodide (1.0M), I2 (0.15M), NBB (0.5M), and GuNCS (0.1 M) in methoxypropionitrile and electrolyte B: 1,3-dimethylimidazolium iodide/1-ethyl-3-methylimidazolium iodide/1-ethyl-3-methylimidazolium iodide/I2/NBB/GuNCS (molar ratio: 12/12/16/1.67/3.33/0.67) and sulfolane (1:1 v/v). The samples were prepared either in ambient air or under strict atmospheric moisture control in a glove box We extracted samples of the dispersion at regular intervals desorbed the dye from the TiO2 particles and analyzed its by HPLC coupled to UV/Vis and electro spray mass spectrometry. Samples prepared in the glove box gave the highest stability with a steady state photo anode surface concentration of 80% C106 intact and the remaining ~20% being the N-butylbenzimidazole (NBB) substitution products 3 and 4 formed by replacement of the thiocyanate ligand by NBB after 1500 hours of heating at 80 ºC. Samples prepared under ambient conditions gave a steady state C106 concentration of 60% of the initial value and 40 % substitution products. The C106 degradation was found to be independent of the degree of dye loading of the TiO2 particles and the ratio between the amount of dyed TiO2 particles and electrolyte volume. Assuming that this substitution is the predominant loss mechanism in a DSC during thermal stress, we estimate the reduction in the DSC efficiency after long term heat to be 12-24% depending on the degree of atmospheric control during the DSC fabrication.
Lund, T., Phuong, N. T., Pechy, P., Zakeeruddin, S. M., Grätzel, M., & Tran, H. M. (2014). Thermal stability of the DSC ruthenium dye C106 in robust electrolytes. Solar Energy, 110, 96-104. https://doi.org/10.1016/j.solener.2014.09.007