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

Abstract 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.