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 (>106 s−1) in doped films. More importantly, replacing the spiro‐centered sp3 C atom (TDBA‐DPAC) with the larger‐radius sp3 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. Conformational heterogeneity in bulky‐group‐shielded deep‐blue thermally activated delayed fluorescent emitters enables suppression of spectral broadening, redshifting, and concentration quenching. Devices based on the emitter present high external quantum efficiency up to 22.35% with suppressed efficiency roll‐off and color indices close to Rec.2020 blue gamut over a wide doping range of 10–50 wt%.