Low efficiency roll-off and high performance OLEDs employing alkyl group modified iridium(iii) complexes as emitters

Abstract

Significant efficiency roll-off of phosphorescent organic light-emitting diodes (PHOLEDs) is a long-standing issue that limits their wider application. To address this problem, four iridium(III) complexes modified by methyl or tert-butyl groups were designed and synthesized, denoted as Me-Ir-PI, tBu-Ir-PI, Me-Ir-PB, and tBu-Ir-PB. Their photophysical, electrochemical, and electroluminescent properties were studied in detail. The electroluminescent performances of devices based on tBu-Ir-PI and tBu-Ir-PB were better than those based on Me-Ir-PI and Me-Ir-PB. The best performance was achieved by the doped device employing tBu-Ir-PI as the emitter with maximum current efficiency of 42.0 cd A⁻¹ and maximum power efficiency of 27.0 lm W⁻¹. Even at a practical brightness of 1000 cd m⁻², the current efficiency and power efficiency remained as high as 39.2 cd A⁻¹ and 22.3 lm W⁻¹. Notably, all doped devices exhibited low efficiency roll-off, especially for device incorporation of tBu-Ir-PB as the guest emitter, which had extremely low roll-off of 0.9%. Meanwhile, non-doped devices based on these iridium(III) complexes also displayed good EL performances.