Deep‐Blue OLEDs with Rec.2020 Blue Gamut Compliance and EQE Over 22% Achieved by Conformation Engineering

To achieve high‐efficiency deep‐blue electroluminescence satisfying Rec.2020 standard blue gamut, two thermally activated delayed fluorescent (TADF) emitters are developed: 5‐(2,12‐di‐ tert ‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐ de ]anthracen‐7‐yl)‐10,10‐diphenyl‐5,10‐dihydrodibenzo[ b,e ][1,4]azasiline (TDBA‐PAS) and 10‐(2,12‐di‐ tert ‐butyl‐5,9‐dioxa‐13b‐boranaphtho[3,2,1‐ de ]anthracen‐7‐yl)‐9,9‐diphenyl‐9,10‐dihydroacridine (TDBA‐DPAC). Inheriting from their parented organoboron multi‐resonance core, both emitters show very promising deep‐blue emissions with relatively narrow full width at half‐maximum (FWHM, ≈50 nm in solution), high photoluminescence quantum yield (up to 92.3%), and short emission lifetime (≤2.49 µs) with fast reverse intersystem crossing (>10 6 s −1 ) in doped films. More importantly, replacing the spiro‐centered sp 3 C atom (TDBA‐DPAC) with the larger‐radius sp 3 Si atom (TDBA‐PAS), enhanced conformational heterogeneities in bulky‐group‐shielded TADF molecules are observed in solution, doped film, and device. Consequently, OLEDs based on TDBA‐PAS retain high maximum external quantum efficiencies ≈20% with suppressed efficiency roll‐off and color index close to Rec.2020 blue gamut over a wide doping range of 10–50 wt%. This study highlights a new strategy to restrain spectral broadening and redshifting and efficiency roll‐off in the design of deep‐blue TADF emitters.