|The organic magnetoresistance effect has been observed to alter the current and
efficiency of organic light emitting diodes where no magnetic materials are present.
As yet, no consensus has been reached in the literature regarding the origin of the
magnetic field effect, though several models have been proposed that feature different
charge species playing the key role, including polaron pairs, triplet excitons,
and bipolarons. Each model relies on some mechanism of spin mixing, commonly
presumed to be hyper fine interactions between polarons and hydrogen nuclei in the
active layer. Through measurements of the relative change in current and effciency
with magnetic field, this thesis utilises slight alterations to the device properties,
namely deuteration of the active layer, and the addition of a doped sensing layer,
to address the assumption about the importance of the hyper fine interaction and to
attempt to di erentiate between the di erent models for organic magnetoresistance.
It is found that the hyper fine interaction is not the only spin mixing mechanism
occurring in the active layer, and that triplets play a pivotal role in the organic
magnetoresistance effect, potentially defining the profile of the organic magnetoresistance
response in doped devices through their population profile.