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Application of Light-Emitting Electrochemical Cells Based on Cyclometalated Iridium Complexes

Light-emitting electrochemical cells (LECs), which contain ionic compounds in the light-emitting layer, have attracted considerable interest for their solid-statelighting and next generation display applications. Compared with conventional organic light-emitting diodes (OLEDs), LECs contain simple device architecture (generally only one light-emitting layer), and can use air-stable metals ( e.g. Al, Ag and Au) as the cathodes directly. In particular, LECs based on ionic transition metal complexes (iTMCs) have received more attention because of their several advantages over conventional polymer-based LECs. For iTMCs-based LECs, no inorganic salt or ion-conducting polymer is needed because iTMCs are intrinsically ionic. Higher efficiency is expected for iTMCs-based LECs because iTMCs emit efficient phosphorescence at room temperature as they can harvest both singlet and triplet excitons. Compared to other iTMCs, ionic iridium complexes have been widely utilized in optoelectronics, owing to their relevant luminescent properties, such as high emission quantum yields, stability and easy tunability of the emission color. The recent research progress of iridium complexes applied in LECs, including their synthesis, structural characterization and optoelectronic properties is summarized. This review mainly focuses on the development of ionic iridium complex-based LECs with different light-emitting colors and the improvement of device performances. In addition, the future directions of iridium complexes in LECs are also discussed.