Molecular Engineering of Donor/π‐Bridge Enables High‐Efficiency and Long‐Lifetime Near‐Infrared TADF‐OLEDs

Abstract

The development of high‐efficiency near‐infrared (NIR) organic emitters has been severely constrained by strong and unavoidable non‐radiative decay governed by the “energy gap law”, which leads to low emission efficiencies and limited options for molecular design. Herein, comparative studies are performed on six‐ and five‐membered π‐bridge and a novel benzo[b]thiophene‐based donor is designed through elaborate molecular engineering, which outperforms widely‐used triphenylamine derivatives in constructing NIR thermally activated delayed fluorescence emitters. The benzo[b]thiophene donor/π‐bridge endows the newly synthesized molecule tBTAP with multiple advantages, including longer emission wavelength and enhanced oscillator strength compared with thiophene‐free triphenylamine donor, and suppressed high‐frequency vibrations compared with thiophene‐inserted donor. Consequently, tBTAP doped and nondoped films display pure NIR emission at peak wavelengths of 795 nm and 854 nm with state‐of‐the‐art photoluminescence quantum yields of 17.9 ± 0.3% and 4.6 ± 0.4%. The corresponding NIR OLEDs demonstrate record‐high maximum external quantum efficiencies of 3.64% (796 nm) and 1.20% (867 nm). Most importantly, nondoped device exhibits record‐long operational lifetime (LT97) of over 2150 h at 10 mA cm−2 for NIR OLEDs. This study signifies an advance in molecular engineering by designing alternative donor/π‐bridge structure, breaking through the bottleneck in developing high‐performance NIR organic emitters and devices toward practical applications.