Efficient and Long Lived Green Light‐Emitting Electrochemical Cells

Abstract

AbstractThe combination of high efficiencies and long lifetime in a single light‐emitting electrochemical cell (LEC) device remain a major problem in LEC technology, preventing its application in commercial lighting devices. Three green light‐emitting cationic iridium‐based complexes of the general composition [Ir(C^N)2(N^N)][PF6] with 4‐Fppy (2‐(4‐fluorophenyl)pyridinato) as the cyclometalating C^N ligand and 1,10‐phenanthroline (1), 4,7‐diphenyl‐1,10‐phenanthroline (bathophenanthroline, bphen, 2), and 2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (bathocuprione, dmbphen, 3) as ancillary N^N ligands are synthesized and characterized. Computational studies are carried out in order to compare the electronic structure of the three ionic transition metal complexes (iTMCs) and provide insights into their potential as LEC emitter materials. LECs are then fabricated with complexes 1–3. Driven under a pulsed current, they display a high luminance and current and power efficiencies. As the LEC based on complex 2 displays the overall best device performance, including the longest lifetime of 474 h, it is selected for subsequent driving conditions optimization. An extraordinary power efficiency of 25 lm W−1 and current efficiency of 30 cd A−1 are achieved under optimized operation conditions with reduced current density, resulting in a long device lifetime of 720 h. Altogether, ligand design in iTMCs and optimization of the device driving conditions leads to a significant improvement in LEC performance.