Reduced concentration quenching in a TADF-type copper(I)-emitter

Phosphorescent OLEDs are now being used in first commercial products, mainly in displays. Typically, such devices operate at low-to-moderate brightnes s (<500 cd m(-2)), while it would be beneficial for actual lighting applications to also reach a very high luminance. However, a phenomenon called efficiency roll-off contradicts this aim. The reducing of the device efficiency with rising triplet exciton concentration due to triplet-triplet annihilation (TTA) is the most relevant factor causing roll-off for such compounds. Photophysically, this is reflected by strong concentration quenching in concentrated samples of phosphorescent materials. We present a potential solution for this issue. In this article we identify a copper(I) emitter showing thermally-activated delayed fluorescence (TADF) that seems to be much more immune to concentration quenching than conventional phosphorescent materials, even though triplet states are also populated in a similar manner.