Tetradentate Pt(II) Complexes with Bulky Carbazole Moieties for High‐Efficiency and Narrow‐Emitting Blue Organic Light‐Emitting Devices

Abstract Blue tetradentate Pt(II) complexes, Pt‐tBuCz and Pt‐dipCz, are synthesized by introducing carbazoles with bulky substituents for improving the rigidity and inhibiting intermolecular interactions of phosphorescent emitter. tert ‐Butyl and 2,6‐diisopropylphenyl groups are substituted as the blocking groups at 3 position of the carbazole in Pt‐tBuCz and Pt‐dipCz , respectively. These new phosphorescent emitters exhibit a narrow full width at half maximum (FWHM) and a high horizontal emitting dipole orientation ratio. Pt‐dipCz demonstrates a small FWHM of 24 nm, a high emitting dipole orientation ratio of 81%, and a high photoluminescence quantum yield value of 94%. As a result, the Pt‐tBuCz and Pt‐dipCz devices exhibited external quantum efficiencies (EQEs) of 23.7% and 25.0% with small FWHMs of 25 and 22 nm, respectively. For the Pt‐dipCz device, the small FWHM and high EQE of >20% are maintained even at a doping concentration of 20 wt%. Furthermore, phosphor‐sensitized organic light‐emitting diodes fabricated using Pt‐dipCz as a sensitizer achieved a high EQE of 31.4% with an FWHM of 18 nm. This result indicates that the 2,6‐diisopropylphenyl group is a effective blocking group for Pt(II) complexes to develop highly efficient, color stable, doping concentration resistant, and efficiently sensitizing blue phosphors.