Efficient organic light-emitting diodes with low efficiency roll-off using iridium emitter with 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenol as ancillary ligand

Using 2,4,5-trifluorophenylpyridine as a monoanionic cyclometalated ligand, 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenol, 2-(5-(4-fluorophenyl)-1,3,4-oxadiazol-2-yl)phenol and 2-(5-(4-trifluoro-methylphenyl)-1,3,4-oxadiazol-2-yl)phenol as ancillary ligands, three new heteroleptic iridium(III) complexes (Ir(F3,4,6ppy)2POP, Ir(F3,4,6ppy)2FPOP and Ir(F3,4,6ppy)2CF3POP) were developed. All complexes are green phosphors (λmax = 503–521 nm) with photoluminescence quantum efficiency yields of 12–18% in CH2Cl2 solutions at room temperature, respectively. The organic light emitting diodes (OLEDs) with the structure of ITO/TAPC (1,1-bis(4-(di-p-tolylamino)phenyl)cyclohexane, 60 nm)/Ir(F3,4,6ppy)2POP (6, 8, 10 wt%): SimCP2 (bis(3,5-di(9H-carbazol-9-yl)phenyl)diphenylsilane, 30 nm)/TPBi (1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl, 90 nm)/LiF (1 nm)/Al (100 nm) showed good performances. Particularly, the device with 8 wt% doped concentration exhibited superior performances with a peak current efficiency (ηc) of 61.49 cd A−1 and a peak power efficiency (ηp) of 46.03 lm W−1. Furthermore, the efficiency roll-off ratios from the peak current efficiency to that at the practical luminance of 100 cd m−2 and from 100 cd m−2 to the benchmark brightness of 1000 cd m−2 in this device are low, which are helpful to keep high efficiency at relatively high current density and high luminance.