Exciplex dynamics in a conjugated polymer blend of MDMO-PPV and PCNEPV

The photophysical properties of a solution processed blend of two semiconducting polymers with electron donating and electron accepting properties, respectively, as used in polymer photovoltaic devices have been investigated. In the binary mixture of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and poly[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV) photoexcitation of either one of the polymers results in formation of a luminescent exciplex at the interface of the two materials. The high energy of this correlated charge-separated state is consistent with the high open-circuit voltage of the corresponding solar cells (1.36 eV). Application of an electric field results in dissociation of the marginally stable exciplex into charge carriers, which provides the basis for the photovoltaic effect of this combination of materials.