Device spectroscopy of magnetic field effects in a polyfluorene organic light-emitting diode

We perform charge-induced absorption and electroluminescence spectroscopy in a polyfluorene organic magnetoresistive device. Our experiments allow us to measure the singlet exciton, triplet exciton, and polaron densities in a live device under an applied magnetic field and to test the predictions of three different models that were proposed to explain organic magnetoresistance. These models are based on different spin-dependent interactions, namely, exciton formation, triplet-exciton polaron quenching, and bipolaron formation. We show that the singlet exciton, triplet exciton, and polaron densities and conductivity all increase with increasing magnetic field. Our data appear to be inconsistent with the exciton formation and triplet-exciton polaron quenching models.