Origin and the role of device physics in the magnetic field effect in organic semiconductor devices

A small magnetic field (~30 mT) can effectively modulate the electroluminescence, conductance and/or photocurrent of organic semiconductor based devices, up to 10% at room temperature. This organic magnetic field effect (OMFE) is one of the most unusual phenomena of both organic electronics and, more basically, magnetism, since all device components are nonmagnetic. However, in spite of latest surge of research interest, its underlying mechanism is still hotly debated. Here we experimentally identify that the magnetic field induced increase of intersystem crossing rate (between either excitons or polaron pairs), and decrease of triplet exciton-polaron quenching rate are responsible for the observed OMFEs. The diversity of observed OMFE results, such as sign change and operating condition dependence, originates from the difference of devices physics.