Decreased Interfacial Charge Recombination Rate Constants with N3-Type Sensitizers

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'-(CO2H)(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, 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.