Efficient Light‐Emitting Electrochemical Cells (LECs) Based on Ionic Iridium(III) Complexes with 1,3,4‐Oxadiazole Ligands

Abstract Eight new iridium (III) complexes 1‐8, with 1, 3, 4‐oxadiazole (OXD) derivatives as the cyclometalated CN ligand and/or the ancillary NN ligands are synthesized and their electrochemical, photophysical, and solid‐state light‐emitting electrochemical cell (LEC) properties are investigated. Complexes 1, 2, 7 and 8 are additionally characterized by single crystal X‐ray diffraction. LECs based on complexes 1‐8 are fabricated with a structure indium tin oxide (ITO) /poly (3, 4‐ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT: PSS) /cationic iridium complex: ionic liquid/Al. LECs of complexes 1 – 6 with OXD derivatives as the cyclometalated ligands and as the ancillary ligand show yellow luminescence (λ max = 552–564 nm). LECs of complexes 7 and 8 with cyclometalated CN phenylpyridine ligands and an ancillary NN OXD ligand show red emission (λ max 616–624 nm). Using complex 7 external quantum efficiency (EQE) values of >10% are obtained for devices (210 nm emission layer) at 3. 5 V. For thinner devices (70 nm) high brightness is achieved: red emission for 7 (8528 cd m −2 at 10 V) and yellow emission for 1 (3125 cd m −2 at 14 V).