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 (ΔE_ST) 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, CIE_y ⩽ 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.