  Spin-dependent processes play a crucial role in organic electronic devices.
Spin coherence can give rise to spin mixing due to a number of processes such
as hyperfine coupling, and leads to a range of magnetic field effects. However,
it is not straightforward to differentiate between pure single-carrier
spin-dependent transport processes which control the current and therefore the
electroluminescence, and spin-dependent electron-hole recombination which
determines the electroluminescence yield and in turn modulates the current. We
therefore investigate the correlation between the dynamics of spin-dependent
electric current and spin-dependent electroluminescence in two derivatives of
the conjugated polymer poly(phenylene-vinylene) using simultaneously measured
pulsed electrically detected (pEDMR) and optically detected (pODMR) magnetic
resonance spectroscopy. This experimental approach requires careful analysis of
the transient response functions under optical and electrical detection. At
room temperature and under bipolar charge-carrier injection conditions, a
correlation of the pEDMR and the pODMR signals is observed, consistent with the
hypothesis that the recombination currents involve spin-dependent electronic
transitions. This observation is inconsistent with the hypothesis that these
signals are caused by spin-dependent charge carrier transport. These results
therefore provide no evidence that supports earlier claims that spindependent
transport plays a role for room temperature magnetoresistance effects. At low
temperatures, however, the correlation between pEDMR and pODMR is weakened,
demonstrating that more than one spin-dependent process influences the
optoelectronic materials properties.
