The Relation between Spin-circulation and Roll-off Behavior of TADF-based OLEDs with Fast Reverse Intersystem Crossing

Abstract

Reverse intersystem crossing (RISC), if efficient in the ambient temperature, is an effective route to harvest triplet excitons with high internal quantum efficiency in TADF-based organic light-emitting diodes (OLEDs). However, the relatively long time-scale of the RISC in typical TADF emitters is regarded as a big hurdle in suppressing or at least mitigating the device efficiency roll-off at high brightness level. To cope with such issues, we explore a system that shows a very fast RISC on the order of ca. 108 s-1 by introducing internal heavy atom effect. The study based on the proposed system unravels the relation between the spin-circulation and roll-off behavior with a strong dependence on the positive charge of the nucleus, providing a potential means to mitigate the roll-off behavior at TADF based OLEDs.