Quantitative study of solvent effects on electron injection efficiency for black-dye-sensitized nanocrystalline TiO2 films

The effects of various solvents on the electron injection efficiency for nanocrystalline TiO2 films sensitized with the black dye trithiocyanato(4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine)ruthenium(II) (Ru(tcterpy)(NCS)3) have been studied quantitatively. The electron injection efficiency for the film dried in air was estimated as 0.4 using a time-resolved microwave conductivity technique. Using transient absorption measurements, we estimated the efficiency of electron injection for TiO2 films in various solvents. Acetonitrile, which is widely considered to be the best solvent for solar cell performance, had the highest efficiency (∼0.65), and other solvents (3-methoxypropionitrile, γ-butyrolactone, and propylene carbonate) had lower efficiencies. These results suggest that characteristic interactions between the black dye and the –CN groups of solvents are important for achieving higher electron injection efficiency.