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

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.