Highly Robust CuI‐TADF Emitters for Vacuum‐Deposited OLEDs with Luminance up to 222 200 cd m−2 and Device Lifetimes (LT90) up to 1300 hours at an Initial Luminance of 1000 cd m−2

Abstract A critical step in advancing the practical application of copper‐based organic light‐emitting diodes (OLEDs) is to bridge the large gap between device efficiency and operational stability at practical luminance. Described is a panel of air‐ and thermally stable two‐coordinate Cu I emitters featuring bulky pyrazine‐ (PzIPr) or pyridine‐fused N‐heterocyclic carbene (PyIPr*) and carbazole (Cz) ligands with enhanced amide‐Cu‐carbene bonding interactions. These Cu I emitters display thermally activated delayed fluorescence (TADF) from the 1 LL′CT(Cz→PzIPr/PyIPr*) excited states across the blue to red regions with exceptional radiative rate constants of 1.1–2.2×10 6 s −1 . Vapour‐deposited OLEDs based on these Cu I emitters showed excellent external quantum efficiencies and luminance up to 23.6 % and 222 200 cd m −2 , respectively, alongside record device lifetimes (LT 90 ) up to 1300 h at 1000 cd m −2 under our laboratory conditions, highlighting the practicality of the Cu I ‐TADF emitters.