Charged dinuclear Cu(I) complexes for solution-processed single-emitter warm white organic light-emitting devices

A series of charged dinuclear Cu(I) complexes were developed by functionalization of both central bipyrimidine-based ligands and organic phosphine ligands. The chemical modification of the ligands can effectively affect the absorption, emission and thermal stability properties of the Cu(I) complexes. The decomposition temperatures (T_d) are improved by using bulky ligands. Interestingly, the complexes with the triphenylamine group on the bipyrimidine ligand show higher photoluminescence quantum yield (PLQY) than the complexes bearing the triphenylphosphine oxide group, while the complexes having the triphenylamine group on the phosphine ligand display lower PLQY. The functional groups also show an obvious influence on the redox behaviors of these complexes. Most importantly, the organic light-emitting diodes (OLEDs) based on selected dinuclear Cu(I) complexes show impressive EL features. The best performance is achieved by the device based on complex Cu-MD-1 with the maximum external quantum efficiency (EQE) of 6.09%, current efficiency (CE) of 12.78 cd A⁻¹ and power efficiency (PE) of 5.93 lm W⁻¹, representing the state-of-the-art EL efficiencies reported for the charged Cu(I) complexes. In addition, the OLEDs based on these Cu(I) complexes can emit warm white light with Color Rendering Index (CRI) as high as 88 and Commission Internationale Ed I'eclairage (CIE) coordinates close to (0.40, 0.46), showing the great potential of these Cu(I) complexes in fabricating single-emitter warm WOLEDs.