Efficient and Saturated Red Light‐Emitting Electrochemical Cells Based on Cationic Iridium(III) Complexes with EQE up to 9.4 %

Abstract

Solid‐state light‐emitting electrochemical cells (LECs) have several advantages, such as low‐voltage operation, compatibility with inert metal electrodes, large‐area flexible substrates, and simple solution‐processable device architectures. However, most of the studies on saturated red LECs show low or moderate device efficiencies (external quantum efficiency (EQE) <3.3 %). In this work, we demonstrate a series of five red‐emitting cationic iridium complexes (RED1‐‐RED5) with 2,2′‐biquinoline ligands and test their electroluminescence (EL) characteristics in LECs. The Commission Internationale de l′Eclairage (CIE) 1931 coordinates for the LECs based on these complexes are all beyond the National Television System Committee (NTSC) red standard point (0.67, 0.33). The maximal EQE of the neat‐film RED1‐based LECs reaches 7.4 %. The reddest complex, RED3, is doped in the blue‐emitting host complex, BG, to fabricate host–guest LECs. The maximal EQE of the host–guest LECs (1 wt % complex RED3) reaches 9.4 %, which is among the highest reported for the saturated red LECs.

Combinational Approach To Realize Highly Efficient Light-Emitting Electrochemical Cells

“…Most important of all, the phosphorescent nature of iTMCs commonly results in more efficient electroluminescence (EL) than other fluorescent materials. Some LECs employing efficient iTMCs were reported to achieve similar device performance to that published for OLEDs. − In addition to efficient emissive materials, optimizing the carrier balance, that is, balancing the number of electrons and holes, of LECs is critical to take full advantage of efficient emissive materials. Several device engineering methods to improve the balance of carrier transport, for example, carrier trapping or blocking, − adjusting carrier injection, − salt incorporation, − modifying carrier transporting, − emissive-layer thickness optimization, − and optimizing emission zone position ,,− were shown for improving the device performance of LECs .…”

Hybrid White‐Light‐Emitting Electrochemical Cells Based on a Blue Cationic Iridium(III) Complex and Red Quantum Dots

“…Several LECs based on efficient iTMCs have been reported to achieve comparable device efficiencies to those measured for OLEDs [19–25] . However, most high‐efficiency iTMCs are blue, [22–24] green, [19, 20] and yellow, [25] whereas the reported red iTMCs commonly show lower photoluminescence quantum yields, [26–29] which limit further enhancement of the device efficiency of host–guest white LECs based on iTMCs. Recently, incorporation of efficient QDs in LECs [30–32] has inspired the idea of the hybrid white LECs combining a yellow iTMC and blue QDs [33] .…”

New molecularly engineered binuclear ruthenium(ii) complexes for highly efficient near-infrared light-emitting electrochemical cells (NIR-LECs)

“…[29][30][31] Accordingly, it was shown that the increasing of the hydrophobicity of the active layer by introducing the hydrophobic side group and the formation of a supramolecular cage by intramolecular face-to-face π-π stacking interactions in the structure of the emitter can also be effective in preventing nucleophiles from gaining access to the metal center, thus leading to more desirable device stability. [32][33][34][35][36][37][38] Another way to increase the stability of LECs is to increase the number of metal centers. 39 Therefore, the use of multi-nuclear complexes can be a convenient method to increase the stability of devices.…”