Thin Film Actinometers for Transient Absorption Spectroscopy: Applications to Dye-Sensitized Solar Cells

The chromophores Ru(bpy) 3 (PF 6 ) 2 and Os(bpy) 3 (PF 6 ) 2 were immobilized within poly(methyl methacrylate) (PMMA) thin films on glass substrates for applications as actinometers for nanosecond flash photolysis. Transient absorption difference spectra of M(bpy) 3 (PF 6 ) 2 (M = Ru, Os), at ambient temperature and in an argon atmosphere, were the same when imbedded in PMMA films as in solution, within experimental error. Linear ranges of Δ A versus 532 nm pulsed laser energy where these actinometers were applicable were identified, up to 25 mJ/(cm 2 pulse) for Ru(bpy) 3 2+ /PMMA and up to 5 mJ/(cm 2 pulse) for Os(bpy) 3 2+ /PMMA. Laser energy measurements were used to estimate the difference between the excited- and ground-state extinction coefficients at 450 nm for Os(bpy) 3 2+, Δε 450nm, which is −7300 M - 1 cm - 1 . The Ru(bpy) 3 2+ /PMMA actinometer was useful from 300 to ∼550 nm, while the Os(bpy) 3 2+ /PMMA actinometer extends the sensitivity to ∼700 nm. An application of these actinometers for dye-sensitized solar cells is described, wherein the quantum yield for electron injection from Ru(dcbH 2 )(bpy) 2 2+ *, where dcbH 2 is 4,4‘-(CO 2 H) 2 -2,2‘-bipyridine, into mesoporous nanocrystalline (anatase) TiO 2 thin films was quantified as a function of ionic strength.