Dendritic Interfacial Exciplex Hosts for Solution-Processed TADF-OLEDs with Power Efficiency Approaching 100 lm W-1

Two kinds of interfacial exciplex hosts formed between a dendritic oligocarbazole donor (H2) and two pyridine-containing isomeric acceptors (B4PyMPM and B3PyMPM) are developed for solution-processed thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs). The exciplex hosts exhibit small singlet-triplet energy splitting (90-110 meV) and distinct TADF effect which can convert triplet excitons into singlet ones and thus are beneficial for alleviating the triplet annihilation process. Notably, it is found that a small structural variation of acceptor from B4PyMPM (para-linked pyridyl units) to B3PyMPM (meta-linked pyridyl units) has a significant effect on enhancing carrier balance between donor and acceptor layers of interfacial exciplex, leading to greatly improved electroluminescent efficiency for the resultant devices. Solution-processed TADF-OLEDs based on H2/B3PyMPM interfacial exciplex host achieve the maximum power efficiency (PE) of 95.0 lm W-1 (85.5 cd A(-1), 26.4 %), which is much better than that of H2/B4PyMPM devices (69.9 lm W-1) and represents the record PE for solution-processed TADF-OLEDs.