Magnetic field dependence of photocurrent in thermally evaporated rubrene-based devices

The magnetic field response of photocurrent in thermally evaporated rubrene-based single layer devices was investigated, with the results revealing a change of sign in magneto-photocurrent (MPC) with a change of bias. Specifically, under forward bias, there was a positive MPC for |B| > 50 mT, while otherwise there was a negative MPC at smaller fields, forming a “W” shape at low magnetic fields. In contrast, the sign of the MPC was completely changed under reverse bias, forming an “M” shape at low magnetic fields (|B| < 50 mT). Our study suggests that the observed MPC was not only related to the singlet fission (SF) process itself but also strongly dependent on the subsequent decay routes of triplets in rubrene. The triplet-charge reaction and triplet dissociation superimposed on SF under magnetic fields were proposed to account for the different MPC under forward and reverse bias, respectively. Moreover, the magnitude of both the positive and negative MPC could be promoted by avoiding the triplet loss channel of triplet-triplet annihilation in the rubrene devices.