High Efficiency and Low Roll-Off Ultraviolet OLEDs Utilizing Robust Hybridized Local and Charge-Transfer Materials with Planarizing Excited State Geometry

The serious efficiency roll-off in the ultraviolet organic light-emitting diodes (UV-OLEDs) limits their potential for advanced applications under high-brightness conditions. In this work, two high-performance asymmetric donor-acceptor-donor’ type tetrafluorobenzene-bridged fluorophores (mPIoCZ4F and mPImCZ4F) are developed with a hybridized local and charge-transfer state characteristic. The planarized excited state conformation induced by intramolecular non-covalent interactions endows the emitters with high radiative rate and fluorescence efficiency, while simultaneously preserving effective UV emission. The doped devices utilizing mPIoCZ4F and mPImCZ4F as emitters exhibit high color purity with electroluminescence peaks of 391 and 389 nm, and full-width at half-maximums of 41 and 39 nm, as well as impressive external quantum efficiencies (EQEs) exceeding 8.3%. Due to the multi-channel high-lying reverse intersystem crossing and limited intersystem crossing, mPIoCZ4F-based device exhibits a more excellent EQE of 8.91%, and remains 8.84% and 8.15% at 500 and 1000 cd m⁻², indicating a minimal efficiency roll-off. Such outstanding performance provides the possibility for UV-OLEDs to be utilized in high-brightness applications.