Improved Operational Stability of Blue Phosphorescent OLEDs by Functionalizing Phenyl-Carbene Groups of Tetradentate Pt(II) Complexes

Stable and efficient deep-blue organic light-emitting diodes (OLEDs) are in high demand for display and lighting applications but are rarely reported due to their poor operational lifetimes. Herein, the study designs and synthesizes two novel N-heterocyclic carbene (NHC)-based tetradentate Pt(II) complexes PtON5-dtb and PtON5N-dtb, and thoroughly investigate their electrochemical and photophysical properties. Functionalization of the NHC moieties can increase the metal-to-ligand charge transfer (1/3MLCT) characters in their lowest triplet excited-states, resulting in significantly shortened photoluminescent lifetimes and remarkably improved device performance. A deep blue OLED employing PtON5N-dtb as an emitter exhibits a narrow spectral bandwidth with a full-width at half maximum (FWHM) of 30 nm and a CIEy value of 0.17 and demonstrates a maximum external quantum efficiency (EQE) of 20.4% with a small efficiency roll-off, which maintains a high EQE of 18.5% at 1000 cd m-2. Moreover, the deep blue OLED also realizes a long-measured operational lifetime LT90 (time to 90% of the initial luminance) of 71 hours with an initial brightness of 1134 cd m-2, corresponding to an estimated device lifetime LT90 of 85 h at 1000 cd m-2. This represented an eightfold lifetime improvement for PtON5N-dtb-based deep blue OLED compared to PtON7-dtb in the same device setting. Efficient and stable deep blue phosphorescent OLEDs are developed employing N-heterocyclic carbene (NHC)-based tetradentate Pt(II) complexes as emitters. PtON5N-dtb-based device shows narrow emission spectrum with full-width at half maximum (FWHM) of 30 nm, demonstrates a peak external quantum efficiency (EQE) of 20.4%, and achieves an estimated operational lifetime LT90 of 85 h at an initial brightness of 1000 cd m-2. image