Electric fields are central to the operation of optoelectronic devices based on conjugated polymers as they drive the recombination of electrons and holes to excitons in organic light-emitting diodes but are also responsible for the dissociation of excitons in solar cells. One way to track the microscopic effect of electric fields on charge carriers formed under illumination of a polymer film is to exploit the fluorescence arising from delayed recombination of carrier pairs, a process which is fundamentally spin dependent. Such spin-dependent recombination can be probed directly in fluorescence, by optically detected magnetic resonance (ODMR). It is found that the ODMR signal in a polymer film is quenched in an electric field in the absence of a current, but that, at fields exceeding 1 MV cm(-1), this quenching saturates at a level of at most 50%
