New Mixed‐ C ^ N C ^{^^ N Ligand Tris‐Cyclometalated Ir IIIIII Complexes for Highly‐Efficient Green Organic Light‐Emitting Diodes with Low Efficiency Roll‐Off}

摘要

> This article reports new tris‐cyclometalated Ir III complexes containing mixed‐ C ^ N ligands, ( C ^ N ₁ ) ₂ Ir( C ^ N ₂ ), which are a rarely explored class of complexes. Two mixed 2‐phenylpyridine (ppy)/4‐methyl‐2,5‐diphenylpyridine (mdp) complexes (ppy) ₂ Ir(mdp) 3 and (ppy)Ir(mdp) ₂ 4 have been synthesized and their optoelectronic properties have been systematically characterized. Photoluminescence quantum yield values are 0.76–0.85; excited state lifetimes are 0.07–0.11 μs. Phosphorescent organic light emitting devices (PhOLEDs) based on these emissive complexes in a very simple device architecture reproducibly showed slightly higher external quantum efficiency (EQE) and power efficiency (PE) values compared with devices using the analogous conventional homoleptic Ir complexes Ir(ppy) ₃ and Ir(mdp) ₃ , and the heteroleptic complexes (ppy) ₂ Ir(acac) and (mdp) ₂ Ir(acac). The new complexes (ppy) ₂ Ir(mdp) 3 and (ppy)Ir(mdp) ₂ 4 give PhOLEDs with EQE _max and PE _max values of 26.7 and 26.0?%/94.7 and 94.1 lm?W –1 , respectively, and very high values are retained at the practical luminances of 100 and 1000 cd?m –2 . The values for (ppy) ₂