Efficient vacuum-processed light-emitting diodes based on carbene-metal-amides

Efficient vacuum-processed organic light-emitting diodes (OLEDs) have been fabricated using the carbene-metal-amide material CMA1. Electroluminescence external quantum efficiencies of greater than 24 % have been achieved with host-guest emissive layers utilizing a 1,3-bis(N-carbazolyl)benzene (mCP) host as well as in host-free emissive layers comprising pure CMA1. Furthermore, an external quantum efficiency greater than 26 % has been achieved by substitution of the emissive layer host for a symmetrical, non-polar variant. Electroluminescence spectra are found to depend on both emissive layer doping concentration and the choice of host material, enabling tuning of emission colour from mid-green (Commission Internationale de l’Éclairage co-ordinates [0.24, 0.46]) to sky blue ([0.22 0.35]) without changing dopant. This tuning is achieved without compromising luminescence efficiency (> 80 %) and maintaining a short radiative lifetime of triplets (< 1 µs).