A Small Cationic Organo–Copper Cluster as Thermally Robust Highly Photo- and Electroluminescent Material

Organic light-emitting diodes (OLEDs) are revolutionizing
display
applications. In this aspect, luminescent complexes of precious metals
such as iridium, platinum, or ruthenium still playing a significant
role. Emissive compounds of earth-abundant copper with equivalent
performance are desired for practical, large-scale applications such
as solid-state lighting and displays. Copper­(I)-based emitters are
well-known to suffer from weak spin–orbit coupling and a high
reorganization energy upon photoexcitation. Here we report a cationic
organo-copper cluster [Cu4(PCP)3]+ (PCP = 2,6-(PPh2)2C6H3) that features suppressed nonradiative
decays, giving rise to a robust narrow-band green luminophore with
a photoluminescent (PL) efficiency up to 93%. PL decay kinetics corroborated
by DFT calculations reveal a complex emission mechanism involving
contributions of both thermally activated delayed fluorescence and
phosphorescence. This robust compound was solution-processed into
a thin film in prototype OLEDs with external quantum efficiency up
to 11% and a narrow emission bandwidth (65 nm fwhm).