Transient optical studies of charge recombination dynamics in a polymer/fullerene composite at room temperature

The recombination kinetics of photogenerated charge carriers in a composite of poly[2-methoxy-5- (3('),7(')-dimethyloctyloxy)-1-4-phenylene vinylene], (MDMO-PPV) and the functionalised fullerene 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C-61 are investigated at room temperature by transient absorption spectroscopy. The decay dynamics of positively charged MDMO-PPV polarons were found to be either monophasic or biphasic, depending upon the laser excitation density employed. The slower, power law, decay phase (100 ns-10 ms) is attributed to recombination dynamics of localized polarons, while the fast decay component (<20 ns) is attributed to recombination of relatively mobile polarons observed when the density of localized states is exceeded by the density of photogenerated polarons (similar to10(17) cm(-3)). The implications of these observations are discussed in relation to polymer/C-60 photovoltaic cells. (C) 2002 American Institute of Physics.