Magneto-electrical signatures of spin dependent processes in organic semiconductors

Room temperature quantum and coherent spin phenomena in organic semiconductors have recently gained interest in the scientific community. Besides the potential for future developments towards quantum-based sensors, computing, and information, established technologies like organic light emitting diodes and organic photovoltaics can benefit near term from harnessing higher order effects such as triplet-triplet annihilation (TTA) and singlet fission (SF). Recently, an observed “half-bandgap” emission in small molecule-based OLEDs has been attributed to a Dexter transfer of triplet charge transfer states into triplet exciton states, followed by triplet-triplet annihilation to produce an emitting singlet. We will present on key requirements to be able to observe TTA in Rubrene and DiFTES-ADT, in heterojunction-based OLED devices test structures. We will show that a sub-bandgap turn-on does not require higher order recombination processes such as TTA and is thus not a reliable measure. However, if competing interfacial recombination pathways are suppressed, TTA can be readily observed in the luminescence-current density-voltage characteristics (L-J-V) at mid to high current densities. We will discuss how these processes relate to the observed Magneto-electro-luminescence response.