Photoinduced charge separation and recombination in a conjugated polymer-semiconductor nanocrystal composite

Semiconductor nanocrystals and conjugated polymers are classes of well-known materials with optoelectronic properties. We demonstrate that in a nanocrystalline TiO2/poly(p-phenylene vinylene) (PPV) composite, excitons photogenerated in the polymer can be dissociated at the interface between the components, with electrons transferred to the nanocrystals. We show this and also follow the subsequent recombination using a time-resolved microwave conductivity technique. Recombination proceeds in a complex manner with roughly half of the initial amplitude decaying in 600 ns and the remainder in a biexponential process with time constants and relative amplitudes of 4.3 (0.7) and 80 μs (0.3). Photovoltaic devices were made from the composite films and their properties are discussed in light of the measured recombination rate and a simple carrier transport model.