  We investigated photogeneration yield and recombination dynamics in blends of
poly(3-hexyl thiophene) (P3HT) and
poly[2-methoxy-5-(30,70-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV)
with [6,6]- phenyl-C61 butyric acid methyl ester (PC61BM) by means of
temperature dependent time delayed collection field (TDCF) measurements. In
MDMO-PPV:PC61BM we find a strongly field dependent polaron pair dissociation
which can be attributed to geminate recombination in the device. Our findings
are in good agreement with field dependent photoluminescence measurements
published before, supporting a scenario of polaron pair dissociation via an
intermediate charge transfer (CT) state. In contrast, polaron pair dissociation
in P3HT:PC61BM shows only a very weak field dependence, indicating an almost
field independent polaron pair dissociation or a direct photogeneration.
Furthermore, we found Langevin recombination for MDMO-PPV:PC61BM and strongly
reduced Langevin recombination for P3HT:PC61BM.
