Ganguri Sarada

Substituent position engineering of diphenylquinoline-based Ir(III) complexes for efficient orange and white PhOLEDs with high color stability/low efficiency roll-off using a solution-processed emission layer

Three new heteroleptic Ir(III) complexes o-LIrpic, m-LIrpic, and p-LIrpic (L = CF3DPQ) consisting of 2,4-diphenylquinoline (DPQ) with a –CF3 group at ortho (o)/meta (m)/para (p) positions of the metalated phenyl ring, respectively, as the main ligands were synthesized and used as emitters in phosphorescent organic light-emitting diodes (PhOLEDs). We realized that –CF3 position extremely affects the crucial photophysical and electronic properties such as emission color, photoluminescence quantum yield (PLQY) and energy levels of these Ir(III) complexes resulting in –CF3 position-dependent performance of their PhOLEDs. To verify the effect of –CF3 group position on device performance, three other Ir(III) complexes o-LIrtmd, m-LIrtmd, and p-LIrtmd were synthesized using the same main ligands but a different ancillary ligand. In the two series of Ir(III) complexes, the devices with m-CF3 based complexes are outstanding in performance compared to o- or p-CF3 based ones due to the enhanced PLQY and well suppressed non-radiative deactivations by m-substitution. Finally, the single emission layer solution-processed orange and two-component white PhOLEDs fabricated using m-LIrpic as orange emitter achieved the maximum external quantum efficiency of 17.1% (43.9 cd A−1) and 21.1% (48.8 cd A−1), respectively, with highly stable color coordinates and low efficiency roll-off. This is the highest efficiency reported to date for solution-processed orange PhOLEDs using a small molecular host with easily accessible emitter.

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%.