Horizontally oriented MRCT-type TADF emitter achieving EQE over 40% for Sky-Blue OLED.

Blue emission is crucial for quality white lighting sources. Delving into precise exciton management in the subtle chemical design using organic materials and understanding key insights into organic light-emitting diode efficiency is of prime importance. Herein, we envision a simple design strategy combining short-range charge transfer with main long-range charge transfer and synchronizing their complementary advantages to afford a new paradigm of multi-resonance charge transfer-type thermally activated delayed fluorescence emitters. Modifying the auxiliary push-pull connection between a carbazole donor and a boron-based acceptor core, we construct C-C bond extended DBACzPh and DBADCzPh emitters with strong thermally activated delayed fluorescence emission in solution and thin films. Preferential 100% horizontal molecular orientation results in balanced bipolar carrier transport and effective host-to-dopant energy transfer in a high-polarity host matrix. Thereby, DBADCzPh significantly boosts outcoupling efficiency. This design achieves sky-blue electroluminescence with a very high external quantum efficiency of over 40%, paving the way for future advancements in emitter designs for high-efficiency OLEDs.