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

Abstract

Recently, perovskites have attracted intense attention due to their high potential in optoelectronic applications. Employing perovskites as the emissive materials of lightemitting electrochemical cells (LECs) shows the advantages of simple fabrication process, low-voltage operation, and compatibility with inert electrodes, along with saturated electroluminescence (EL) emission. Unlike in previously reported perovskite LECs, in which salts are incorporated in the emissive layer, the ion-transport layer was separated from the emissive layer in this work. The layer of ionic transition metal complex (iTMC) not only provides mobile ions but also serves as an electron-injection/transport layer. Orthogonal solvents are used in spin coating to prevent the intermixing of stacked perovskite and iTMC layers. The blue iTMC with high ionization potential is effective in blocking holes from the emissive layer and thus ensures EL color saturation. In addition, the carrier balance of the perovskite/iTMC LECs can be optimized by adjusting the iTMC layer thickness. The optimized external quantum efficiency of the CsPbBr 3 /iTMC LEC reaches 6.8 %, which is among the highest reported values for perovskite LECs. This work successfully demonstrates that, compared with mixing all components in a single emissive layer, separating the layer of ion transport, electron injection and transport from the perovskite emissive layer is more effective in adjusting device carrier balance. As such, solution-processable perovskite/iTMC LECs open up a new way to realize efficient perovskite LECs.

Deep-red and near-infrared light-emitting electrochemical cells employing perovskite color conversion layers with EQE >10%

“…20 nm) for our synthesized nanocrystal under the same synthesized conditions. 50 A little overestimation is because Scherrer analysis will be weighted toward larger crystals. 49,51 The sizes of these synthesized nanocrystals are in the range of 20–30 nm.…”

Long‐Wavelength Light‐Emitting Electrochemical Cells: Materials and Device Engineering

“…Several NIR perovskite LEDs showing EQEs >20 % have been reported [167] . Recently, several works about incorporating ionic additives [116–118] and optimizing carrier balance [119] of perovskite green LECs have significantly improved the device efficiencies. If deep‐red or NIR perovskites are used as the emissive materials of LECs, similar techniques can be performed to achieve good device performance.…”

“…Recently, perovskites have attracted much research attention due to easy synthesis, saturated emission and high PLQYs [114] and several works on LECs employing perovskites were reported [115–119] . However, most of them are green LECs and long‐wavelength LECs based on perovskites are relatively rare.…”

Cationic Ir(III) Complexes with 4-Fluoro-4′-pyrazolyl-(1,1′-biphenyl)-2-carbonitrile as the Cyclometalating Ligand: Synthesis, Characterizations, and Application to Ultrahigh-Efficiency Light-Emitting Electrochemical Cells

“…Recently, several materials have been applied to LECs with promising performance. In particular, the structure of phosphorescent ionic transition metal complexes (iTMCs) employed by iridium (Ir) metal, which exhibits a heavy atomic effect giving strong spin–orbit coupling (SOC), promotes singlet–triplet transition and achieves 100% exciton utilization. − Besides, the σ-robust donating ability of carbon atom subtle couples with the heavy atom leading to enhance the SOC effect which can promote the exciton transition to low-lying metal-to-ligand charge transfer state (MLCT), and subsequently yield light emission through the radiative process at the excited triplet state as the El-Sayed rule. − More importantly, the introduction of a rigid ligand can improve high phosphorescence quantum yields (QYs) leading to realize the high efficiency of LECs device. − ,, With these advantages, cationic Ir­(III) complexes have found extensive applications in various aspects of LECs.…”