Decreased Interfacial Charge Recombination Rate Constants with N3-Type Sensitizers

Abstract

Interfacial charge separation and recombination were quantified at sensitized mesoporous nanocrystalline TiO 2 interfaces immersed in acetonitrile electrolyte. Two sensitizers contained a phenylenethynylene spacer between a cis- Ru(NCS) 2 core and TiO 2 anchoring groups, and a third sensitizer did not contain the spacer, cis -Ru(dcb)(bpy)(NCS) 2, where bpy is 2,2′-bipyridine and dcb is 4,4′-(CO 2 H) 2 -bpy. Excited-state injection occurred with approximately the same yield for all these sensitizers and was rapid with k inj > 10 8 s −1 . Representative charge recombination rate constants from nanosecond transient absorption data were quantified by a distribution analysis, based on the Kohlrausch−Williams−Watts model, and were found to be 3 times slower for the sensitizers with the phenylenethynylene spacer. Slow recombination kinetics manifested itself as an increased open circuit photovoltage, V oc . The V oc values measured experimentally were contrasted with calculated values abstracted from the diode equation with ideality factors around 3 and the rate constants for charge recombination measured spectroscopically.