Fast TADF and Its Implication on OLED Device Performance

Abstract

Thermally Activated delayed fluorescence (TADF) can harvest triplet excitons to yield near 100% internal quantum efficiency in organic light-emitting diodes (OLEDs). The process central to this TADF is the reverse intersystem crossing (RISC) that can occuring at room temperature between S1 and T1 excited states. This originates mainly from the small singlet-triplet energy difference, which is related to the electron-exchange energy in quantum theory. Numerous high efficiency OLEDs based on TADF emitters have indeed been demonstrated by many groups, but many of them are still suffering from efficiency roll off at high brightness level. To cope with many demanding requirements of modern display or lighting applications, it is thus crucial to suppress or at least mitigate key processes leading to such behavior. One dominant origin for efficiency roll off in TADF-based OLEDs is the relatively long time scale that takes in T1  S1 spin flipping, which tends to make carriers accumulated and thus increase the probability for exciton quenching at high current densities. In this regard, this talk will introduce systems that can exhibit a very fast TADF with the RISC rate on the order of 107 s-1 and discuss its photophysical impact on device characteristics from both theoretical and experimental perspectives.