Efficient and Long Lived Green Light‐Emitting Electrochemical Cells

Abstract

The 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.

Color‐Stable, Efficient, and Bright Blue Light‐Emitting Electrochemical Cell Using Ionic Exciplex Host

“…A wide variety of emitting materials, [ 2,6,7 ] such as fluorescent polymers and small molecules, [ 1,8,9 ] phosphorescent ionic transition‐metal complexes, [ 10–14 ] thermally‐activated delayed fluorescence (TADF) molecules, [ 15–17 ] quantum dots, [ 18 ] and perovskite, [ 18–20 ] have been used for LECs. With these emitting materials, red to blue and white LECs have been fabricated.…”

“…With these emitting materials, red to blue and white LECs have been fabricated. [ 2–4,8–14,18 ] However, blue LECs have shown inferior performances, [ 12,13 ] which has remained a formidable challenge for the fabrication of white LECs for lighting applications. [ 2–4 ] Color stability, efficiency, brightness and operational stability are four critical parameters to evaluate blue LECs for real‐world applications.…”

Perovskite Light‐Emitting Electrochemical Cells Employing Electron Injection/Transport Layers of Ionic Transition Metal Complexes

“…It enables novel solutionprocess fabrication [4,5] and light-outcoupling optimization by adjusting emission zone position. [6,7] Simple device structure and easy fabrication processes render LECs suitable for use in cost-effective light-emitting devices in lighting [8,9] and display [10,11] applications.…”

Magnetic, Photo- and Electroluminescent: Multifunctional Ionic Tb Complexes

“…With respects to LEC technology, recently, significant progress could be made with respect to green light emitting LECs. 40 − 42 However, the iTMCs used in these devices are based on Ir(III) which is considerably more expensive than Tb(III).…”