Solution-processable highly efficient deep-red and orange organic light-emitting diodes based on multi-functional Ir(iii) complexes†
A heteroleptic deep-red iridium(III) complex, TPQIr-HT, based on thiophene-phenylquinoline (TPQ), and orange Ir(III) complexes, m-CF3DPQIr-HT and m-CF3DPQIr-ET based on diphenylquinoline (DPQ), are designed by attaching a carbazole-based hole transporting (HT) group and an oxadiazole (OXD)-based electron transporting (ET) group to the parent Ir(III) complexes, TPQIr and m-CF3DPQIr. The Ir(III) complexes TPQIr-HT show a deep-red emission peak at 612 nm, similar to that of TPQIr, whereas m-CF3DPQIr-HT and m-CF3DPQIr-ET show an orange emission peak at 567 ± 1 nm, which is similar to that of m-CF3DPQIr. The newly functionalized Ir(III) complexes show improved device performance compared to the Ir(III) complexes, TPQIr and m-CF3DPQIr, without the additional functional groups. The phosphorescent organic light-emitting diodes (PhOLEDs) fabricated using a deep-red Ir(III) complex, TPQIr-ET, achieved a maximum external quantum efficiency (EQE) of 17.47% using GraHIL as the hole injection layer (HIL). Similarly, the orange Ir(III) complex, m-CF3DPQIr-HT, achieved a maximum EQE of 21.61%.