Science 363, 601–606 (2019)

The use of copper complexes to make efficient blue organic light-emitting diodes (OLEDs) has taken a step forward with the demonstration of a two-coordinate Cu(i) complex that offers almost perfect luminescence efficiency. Rasha Hamze and co-workers from the University of California, USA, report that their Cu(i) emitters, CAAC–Cu–amide complexes, emit light with a quantum efficiency of >99% thanks to the absence of non-radiative decay. Blue OLEDs based on the compounds doped in a host of UGH3 emit blue light at around 460 nm and feature a turn-on voltage of around 3 V with a maximum external quantum efficiency of about 9% at a drive current density of 2 mA cm–2.