Efficient and Stable Deep‐Blue Fluorescent Organic Light‐Emitting Diodes Employing a Sensitizer with Fast Triplet Upconversion

Multiple donor–acceptor‐type carbazole–benzonitrile derivatives that exhibit thermally activated delayed fluorescence (TADF) are the state of the art in efficiency and stability in sky‐blue organic light‐emitting diodes. However, such a motif still suffers from low reverse intersystem crossing rates (kRISC) with emission peaks 60 h at an initial luminance of 1000 cd m−2. Multiple donor–acceptor‐type carbazole–benzonitrile derivatives with both linear donor–π–donor and acceptor–π–acceptor structures to promote triplet upconversion are utilized as a sensitizer, realizing organic light‐emitting diodes with deep‐blue narrow‐band emission, maximum external quantum efficiency of 32.5%, and a T80 (time to 80% of the initial luminance) of >3000 h at an initial luminance of 100 cd m−2 simultaneously.