High performance doping-free WOLEDs based on rationally designed asymmetric orange-red Ir(III) emitter with balanced charge mobility

Abstract Doping-free organic light-emitting diodes (OLEDs) have attracted continuous attention owing to reduced phase separation, better repeatability, and low cost. Despite demonstrating great potential for white OLEDs (WOLEDs), development of phosphorescent materials capable of achieving high performance with low voltage, high luminance, and low efficiency roll-off simultaneously, still remains a significant challenge. Herein, we design three orange-red Ir(III) phosphors employing functionalized 1,2-diphenylbenzimidazole as main ligands. Clear relationship between structures and electroluminescence (EL)-performances has been established by comprehensively studying their emission properties and intrinsic carrier transporting abilities. Designed phosphor SFIrbiq with spirobifluorene moiety showing negligible intermolecular interactions and balanced carrier transporting ability, not only achieves favorable monochromatic doping-free device but also high-performance doping-free WOLEDs. Optimized WOLED realizes low voltages (2.5 V at 1 cd m−2, 3.3 V at 100 cd m−2, and 4.2 V at 1000 cd m−2), maximum brightness of 34 505 cd m−2 and efficiencies of 24.2 cd A−1, 21.7 lm W−1, 10.3%. Such doping-free hybrid WOLED also achieves low efficiency roll-off of 5% for external quantum efficiency (EQE) at 1000 cd m−2. The device performance can be further improved by employing doping-free all-phosphorescent device structure, achieving maximum efficiencies of 33.3 cd A−1, 32.4 lm W−1, and 16.9%. The results are promising among reported doping-free three-color WOLEDs, paving a feasible way to development of efficient Ir(III) phosphors and doping-free WOLEDs.