Highly Efficient Non-Doped Phosphorescent Blue OLEDs with Novel Asymmetric Iridium(III) Complexes

Abstract

In this study, three phenylimidazole (pmi)-based asymmetric iridium(III) complexes are successfully developed as promising emitters for non-doped blue organic light emitting diodes (OLEDs). The Ir-3 exhibited blue emission with peak located at 470 nm and a high photoluminescent quantum yield (Φ_PL) of 65% in non-doped film. Single crystal X-ray diffraction analysis revealeds that Ir-3 has increased steric hindrance from bulky tert-butyl groups that effectively suppressed π–π stacking and minimized exciton quenching. The non-doped device based on Ir-3 exhibited superior electroluminescent properties, including a low turn-on voltage of 2.80 V, and achieved maximum efficiencies of external quantum efficiency (EQE_max) of 18.01%, a high power efficiency (PE) of 31.52 lm W⁻¹, which outperform previously reported blue non-doped phosphorescent OLEDs. Moreover, Ir-3-based non-doped devices closely matched the performance of doped counterparts, demonstrating high color stability and strong emission in the blue region of emission peak of 471 nm and CIE coordinates of (0.164, 0.208). This work highlights the potential of robust Ir-3 as a promising emitter for high efficiency, stable blue OLEDs, offering a simplified, host-free device architecture that maintains performance and provides a practical path forward for next-generation display and lighting applications.