Device-spectroscopy of magnetic field effects in several different polymer organic light-emitting diodes

We perform charge-induced absorption and electroluminescence spectroscopy in a set of organic magnetoresistive devices made from different π -conjugated polymers. These experiments measure the singlet exciton, triplet exciton and polaron densities in live devices under an applied magnetic field. In most devices we find that the singlet exciton, triplet exciton and polaron densities and conductivity all increase with increasing magnetic field. However, in regio-regular polythiophene devices the polaron density decreases with increasing field. Our experiments 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.