An in situ heating method was used to investigate the effect of high temperature on the magneto-electroluminescence (MEL) of rubrene-based organic light-emitting diodes. The change of MEL indicated that the microscopic mechanism of the device converted from singlet fission (SF) to intersystem crossing (ISC) at 380 K. Analysis of the surface morphology, electroluminescence spectrum, and current–voltage curve of the device suggested that the SF-to-ISC conversion was caused by a large number of exciton traps generated in the organic layers of the device. These traps blocked the movement of excitons, which suppressed SF. By contrast, ISC was promoted by traps and became the main process. This work provides a detailed investigation of the dynamics of exciton evolution and deepens our understanding of electron–hole interaction mechanisms in organic devices at high temperature.
