Analysis of the mechanism for magneto-conductance induced by triplet-charge interaction by energy resonance of excitons in rubrene
2017
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.
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