Lifetime of triplet excitons in organic LEDs based on thermally activated delayed fluorescence

Organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) are currently limited by their operational stability and a decreased efficiency at high brightness, both of which are strongly related to the interactions between triplet excitons and other quasiparticles. Here, an expression for the lifetime of triplet excitons in TADF OLEDs is derived, which correlates with the efficiency roll-off. The triplet lifetime in a TADF OLED intriguingly can be well approximated by the delayed-fluorescence lifetime of the TADF emitter, enabling facile quantification of the triplet population in a working OLED for investigating triplet-related loss processes, such as the efficiency roll-off and degradation.