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

Abstract

The chromophores Ru(bpy)3(PF6)2 and Os(bpy)3(PF6)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(PF6)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 ΔA versus 532 nm pulsed laser energy where these actinometers were applicable were identified, up to 25 mJ/(cm2 pulse) for Ru(bpy)3 2+/PMMA and up to 5 mJ/(cm2 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+, Δε450nm, 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(dcbH2)(bpy)2 2+*, where dcbH2 is 4,4‘-(CO2H)2-2,2‘-bipyridine, into mesoporous nanocrystalline (anatase) TiO2 thin films was quantified as a function of ionic strength.

Interfacial Electron Transfer Dynamics Following Laser Flash Photolysis of [Ru(bpy)2((4,4′‐PO3H2)2bpy)]2+ in TiO2 Nanoparticle Films in Aqueous Environments

“…[46] Briefly, a thin film of [Ru(bpy) 3 ](PF 6 ) 2 in PMMA on one side of an FTO slide was used as a transient absorption chemical actinometer with known molar extinction coefficient change, e act = De 450 = À10 000 m À1 cm…”

Electron transfer dynamics of peptide‐derivatized RuII‐polypyridyl complexes on nanocrystalline metal oxide films

“…Electron injection yields were measured by using thin film actinometry53 with RuP on TiO 2 in aqueous 0.1 M HClO 4 (Φ nj = 100%) as the reference (Figure S7) 25, 28. The trend in injection yields was reproducible for two separate samples with yields decreasing in the order: Ru‐P0 (11%) > Ru‐P3 (6%) > Ru‐P7 (4%).…”

High Extinction Coefficient Ru‐Sensitizers that Promote Hole Transfer on Nanocrystalline TiO2

“…The electron injection yields for [Ru(deeb) 2 L5] 2 + and [Ru(deeb) 2 L6] 2 + were estimated through comparative actinometry, according to a method described in detail elsewhere. [19] The results suggested a low injection yield, between 5 and 20 % depending on light intensity and sample. This is, however, a conservative estimate because no reliable value for the extinction coefficient of the oxidized state was available and thus, we can only conclude that electron injection into TiO 2 occurred.…”