Alkyl-promoted Iridium Complex for High-Performance Deep-Red Phosphorescent Organic Light-Emitting Diodes

In this work, a novel deep-red (642 nm) iridium complex, Ir(bp4b)(2)(dend), is developed. The introduction of alkyl groups in ligands weakens the intermolecular interactions and endows Ir(bp4b)(2)(dend) with favorable physical properties: short photoluminescence lifetime (271.6 ns), low concentration sensitivity (10(-6) to 10(-4) M) and balanced charge-transporting ability. Ir(bp4b)(2)(dend)-doped phosphorescent device displays high efficiencies (9.62 cd/A, 12.25 mu m/W, 15.29%), low roll-off of efficiencies (from 10 to 1000 cd/m(2): no decrease; from 1000 to 5000 cd/m(2): 10.6%), relatively low concentration sensitivity (from 5% to 15%), long device lifetime (T80: 5225 h at 100 cd/m(2)) and very stable electroluminescent spectra (from 1 cd/m(2) to maximum luminance). This performance is comparable to those of previous record deep-red (around 640 nm) phosphorescent emitters. More importantly, compared with previous record emitters, Ir(bp4b)(2)(dend) reports more kinds of excellent parameters and such comprehensive deep-red emitter is rare at present.