Tetra-coordinated difluoroboron TADF emitter for sky-blue organic light-emitting diodes with 27.4% external quantum efficiency

Tetra-coordinated fluoroboron compounds have garnered significant attention in organic light-emitting diodes（OLEDs） due to their remarkable optoelectronic properties and high chemical stability.However,the design of novel tetra-coordinated fluoroboron-based blue thermally activated delayed fluorescence（TADF） materials with excellent external quantum efficiency（EQE）remains crucial.In this study,a novel tetra-coordinated difluoroboron-based blue TADF material with 3,6-diphenylcarbazole donor and 2-（4-phenylpyridin-2-yl）phenolate difluoroboron acceptor molecular skeleton has been designed and synthesized.Benefiting from the larger dihedral angle（68.0°） between the donor and acceptor moieties,the compound m-PhCz-BF2 exhibited a smaller singlet-triplet energy splitting(ΔEST) value of 0.043 eV.As a result,a sky-blue emission with peak wavelengths of 491 and 487 nm and photoluminescence quantum yields（PLQY） of 93% and 99% were obtained in solution and doped film,respectively.Additionally,the m-PhCz-BF2 doped OLED demonstrated sky-blue electroluminescence（Commission Internationale de l'éclairage,CIEy≤ 0.33） and a high peak EQE of 27.4% with maximum brightness of 17,493 cd/m2.Notably,these devices also achieved a high current efficiency of 62.5 cd/A and a power efficiency of 49.4 lm/W.These remarkable performances indicate that the m-PhCz-BF2 has the potential to function as a highly efficient TADF dopant for the fabrication of sky-blue OLEDs.