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

AbstractA 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 CuI emitters featuring bulky pyrazine‐ (PzIPr) or pyridine‐fused N‐heterocyclic carbene (PyIPr*) and carbazole (Cz) ligands with enhanced amide‐Cu‐carbene bonding interactions. These CuI emitters display thermally activated delayed fluorescence (TADF) from the 1LL′CT(Cz→PzIPr/PyIPr*) excited states across the blue to red regions with exceptional radiative rate constants of 1.1–2.2×106 s−1. Vapour‐deposited OLEDs based on these CuI emitters showed excellent external quantum efficiencies and luminance up to 23.6 % and 222 200 cd m−2, respectively, alongside record device lifetimes (LT90) up to 1300 h at 1000 cd m−2 under our laboratory conditions, highlighting the practicality of the CuI‐TADF emitters.