Deep‐Blue OLEDs With Color Purity Approaching BT.2020 Standard and Blue Index of 464 Enabled by Narrowband Pt(II) Emitters With 3D Geometry

Phosphorescent Pt(II) emitters are promising candidates to overcome the low blue index (BI) issue of commercialized blue organic light‐emitting diodes (OLEDs); however, developing high‐performance deep‐blue OLEDs with high color purity, particularly with a full‐width at half‐maximum (FWHM) of less than 20 nm, is a major challenge. Herein, we report a synergistic design strategy, involving the regulation of both molecular geometry and excited‐state properties to balance the efficiency and color purity of deep‐blue Pt(II) emitter toward the Broadcasting and Television 2020 (BT.2020) standard. A bottom‐emitting OLED displays deep‐blue light peaking at 461 nm, a small FWHM of 19 nm, and high external quantum efficiencies (EQEs) of 29.1% and 22.9% at 1000 and 10000 cd/m 2 , respectively; and realizes a record‐high maximum brightness of 49971 cd/m 2 for non‐sensitized deep‐blue OLEDs with CIE y < 0.15. A top‐emitting OLED exhibits a further narrowed spectrum with a FWHM of 13.3 nm, and achieves a Commission Internationale de l'Éclairage y coordinate (CIE y ) of 0.053, extremely close to the BT.2020 blue standard. This OLED also exhibits an outstanding maximum BI value of 464 cd A −1 CIE y −1 and maintains a BI of 435 cd A −1 CIE y −1 at 1000 cd/m 2 .