Studies of photoinduced charge transfer in conjugated polymer-fullerene composites by light-induced ESR

In this work we present comparative studies of the photoinduced electron transfer (PIT) in a number of conjugated polymer/fullerene composites and in pure components by using light-induced electron spin resonance. PIT from the polymer onto fullerene in the composites results in the appearance of two LESR lines: i) g=2.0025, g=2.0025, attributed to the positive polaron on the polymer chain and ii) g=1.9995 g=1.9995 originating from the fullerene anion-radical. These signals have different spin-lattice relaxation times with different temperature dependencies, the low field line possessing the longer relaxation time. The amount of light induced charges is proportional to the square root of the excitation light intensity, which indicates bimolecular recombination of polarons. Both lines have reversible light-induced ESR components and persistent light-induced contribution attributed to trapped polarons