Platinum(II) Phosphors Featuring 3D Geometry and Locally Excited State for High-Performance Deep-Blue OLEDs

Organic light-emitting diodes (OLEDs) have become mainstream display technology, but it is still limited by the low device efficiency of blue OLEDs, and robust emitters are highly needed for developing high-performance deep-blue OLEDs. In this work, we developed a strategy to design highly efficient tetradentate Pt(II) emitters with extremely narrow emission spectra, which was achieved by endowing their molecular configurations with rigid 3D geometries, along with locally excited (3LE)-dominated lowest excited states (T1) mixed with metal-to-ligand charge transfer (3MLCT) character. PtO1 and PtS1 had high thermal stabilities with 5% weight loss temperature (ΔT5%) values of up to 502 and 516 °C, respectively. A PtS1-based deep-blue OLED exhibited a low turn-on voltage of 2.5 V, a high color purity with a small full-width at half-maximum (FWHM) of 19 nm, and a small Huang–Rhys factor (SM) of 0.290, resulting in Commission Internationale de l’Éclairage (CIE) coordinates of (0.121, 0.167). The OLED also achieved a high maximum brightness of up to 49019 cd/m2 along with a record-high maximum external quantum efficiency (EQE) of 36.5% among all reported deep-blue phosphorescent OLEDs with CIEy < 0.20 and maintained high EQEs of 34.2, 28.1, and 23.6% at 1000, 5000, and 10,000 cd/m2, respectively. This study presents a strategy for designing highly efficient and narrow-spectrum tetradentate Pt(II) complexes for robust deep-blue emitters.