Mitigating the Trade-off betweenTriplet Harvestingand Roll-off by Opening a Dexter-Type Channel in OLEDs

As an approach to overcome the limitation of spin statistics in electroluminescent (EL) system, the use of sensitizing system, employing thermally activated delayed fluorescence (TADF) as an intermediate component or host, has been actively discussed recently. However, the existence of a non-radiative channel (i.e., Dexter energy transfer, DET) from the lowest triplet excited state (T1) in the TADF host or assistant layer still can cause the efficiency drop, although this strategy could break the spin multiplicity. In this context, an approach to break the limitation of the conventional sensitizing system on the basis of Forster resonance energy transfer (FRET) should be developed. Herein, we explore the potential of non-radiative energy loss, a DET type channel, in shortening the triplet exciton residence time in an EL system, thereby achieving both improved efficiency and reduced roll-off. The discussions in the proposed triplet-harvest system raise the following points: (i) the necessity of an assistan...