UC Irvine

Interfacial charge separation and recombination were quantified at sensitized mesoporous nanocrystalline TiO2 interfaces immersed in acetonitrile electrolyte. Two sensitizers contained a phenylenethynylene spacer between a cis-Ru(NCS)2 core and TiO2 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 2H)2-bpy. Excited-state injection occurred with approximately the same yield for all these sensitizers and was rapid with k inj > 108 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, Voc. The Voc 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. © 2010 American Chemical Society.