Analysis of the mechanism for magneto-conductance induced by triplet-charge interaction by energy resonance of excitons in rubrene

To analyze the mechanism for magneto-conductance (MC) induced by triplet-charge interaction (TCI), the rubrene-based organic emitting devices with Al, LiF/Al and Ca acting as metallic cathodes were fabricated, respectively. The MC in Al-cathode device decreases monotonously with increasing external magnetic field, which is obviously different from the one in LiF/Al- or Ca-cathode device. Using the energy resonance of singlet (S) and triplet (T) excitons in rubrene, the singlet fission and triplet fusion was changed to alter the ratio of T. The charge (C) was also changed by metallic cathode modulated electronic injection barrier. Consequently, the TCI was substantially modulated. The results suggested that the negative MC curves were due to the quenching of T exciton by trapped charges via detrapped channel (T+C t →S 0 +C), rather than by dissociation or scattering of excessive charges. It was also suggested that the MC of LiF/Al- and Ca-cathode devices with balanced carriers injection is an order of magnitude smaller than the one of Al-cathode device. Additionally, the MC decreases in low-field region (<100 mT) and then turns to increase with increasing B field. The weak MC in balanced devices is not due to the weakness of TCI, but to the assumption that the existence of detrapping and trapping channels has a weak impact of on electronic current. This is because the traps in active layer of rubrene are fully occupied by minority electrons which are easier injected from cathode. Hence, the carrier traps in quenching way paly a primary role in the MC response of TCI. Our work suggests that producing plenty enough un-occupied carrier traps in organic functional layer is a promising approach to utilize the MC of TCI.