Dinuclearization strategy of cationic iridium(iii) complexes for efficient and stable flexible light-emitting electrochemical cells

Abstract

Light-emitting electrochemical cells (LECs) as simple and low-cost electroluminescent devices are one of the most promising candidates for the next-generation flexible and large-area solid-state lighting applications. However, the development of efficient emissive materials to achieve both excellent efficiency and stability, especially for flexible LECs, remains a challenge. Herein, we demonstrate a remarkable enhancement of overall device performance using a facile and feasible di-nuclearization strategy. The symmetrical dinuclear iridium(III) complex (D-Ir2) and its mononuclear counterpart (M-Ir1) are designed and synthesized. Although it has little effect on the emission color, the adopted approach ingeniously manipulates the intrinsic photophysical processes and solid-packing, leading to distinct LEC performance. Flexible LECs employing D-Ir2 as an emitting layer realizes a current efficiency of 14.2 cd A⁻¹ and external quantum efficiency of 5.1%, almost twice as high as that of M-Ir1. Encouragingly, compared with a short half-lifetime (t_1/2) of 190 min for M-Ir1, the D-Ir2-based LEC demonstrates better stability in the open air with t_1/2 of 312 min. The large decomposition energy of ligands and facile intersystem crossing supported by theoretical calculations account for its superiority. This study will provide a new perspective for constructing phosphorescent materials suitable for high-performance flexible optoelectronics.