Archetype Cationic Iridium Complexes and Their Use in Solid‐State Light‐Emitting Electrochemical Cells

Abstract

The archetype ionic transition‐metal complexes (iTMCs) [Ir(ppy)2(bpy)][PF6] and [Ir(ppy)2(phen)][PF6], where Hppy = 2‐phenylpyridine, bpy = 2,2′‐bipyridine, and phen = 1,10‐phenanthroline, are used as the primary active components in light‐emitting electrochemical cells (LECs). Solution and solid‐state photophysical properties are reported for both complexes and are interpreted with the help of density functional theory calculations. LEC devices based on these archetype complexes exhibit long turn‐on times (70 and 160 h, respectively) and low external quantum efficiencies (∼2%) when the complex is used as a pure film. The long turn‐on times are attributed to the low mobility of the counterions. The performance of the devices dramatically improves when small amounts of ionic liquids (ILs) are added to the Ir‐iTMC: the turn‐on time improves drastically (from hours to minutes) and the device current and power efficiency increase by almost one order of magnitude. However, the improvement of the turn‐on time is unfortunately accompanied by a decrease in the stability of the device from 700 h to a few hours. After a careful study of the Ir‐iTMC:IL molar ratios, an optimum between turn‐on time and stability is found at a ratio of 4:1. The performance of the optimized devices using these rather simple complexes is among the best reported to date. This holds great promise for devices that use specially‐designed iTMCs and demonstrates the prospect for LECs as low‐cost light sources.

Quantum Dot/Light-Emitting Electrochemical Cell Hybrid Device and Mechanism of Its Operation

“…The iTMC shows broad PL (fwhm = 96 nm) centered at a wavelength of 554 nm, which is typical for iTMCs emitters based on charge transfer transitions. 39 Unlike recently shown for hybrid devices based on iTMC and a conjugated polymer, 40 our hybrid devices show a pronounced superposition of iTMC-and QD-PL spectra with a dominating QD-PL peak at 620 nm. It should be noted that no energy shift occurs in the PL of the hybrid device compared to the single components.…”

“…This behavior is also typical for iTMC-emitters and can be attributed to optical and electrical carrier excitation, respectively. 39,44 The EL emission characteristics of the hybrid device are shown in Figure 2. As can be seen from both (a) the color images of the active light-emitting pad and (b) the corresponding normalized EL spectra, the emission color of the QLEC changes significantly with applied voltage.…”

Luminescent Iridium Complexes Used in Light-Emitting Electrochemical Cells (LEECs)

“…6 ] in an otherwise identical device configuration [23]. In the absence of IL, an extremely long t on of more than 70 h is observed.…”

“…Entry 1 effectively demonstrates this principle with the device based on 1 exhibiting a remarkably long lifetime of 668 h. The authors attribute this stability to the relatively large calculated 3 MC-T 1 energy gap for 1 [23]. Theory and experimental observations have implicated 3 MC states in an elongation of the N pyridyl -Ir bond of the C^N ligands of [Ir(C^N) 2 (N^N)] ?…”

New Iridium Complex Coordinated with Tetrathiafulvalene Substituted Triazole-pyridine Ligand: Synthesis, Photophysical and Electrochemical properties

“…15 All solvents were dried using standard procedures. Solvents used for electrochemistry and spectroscopy were spectroscopic grade.…”