High-performance solution-processed orange phosphorescent OLEDs

High-efficiency phosphorescent materials serve as the cornerstone for the advancement of organic light-emitting diodes (OLEDs). It is well-established that the incorporation of nitrogen heterocycles and the modulation of structural rigidity and conjugation can enhance the electron transfer capability and luminous efficiency of the complexes, which are indispensable for achieving high-performance devices. In this study, we report three iridium(III) complexes, namely (4-tfmptp)(2)Ir(pic), (4-tfmptp)(2)Ir(3-ppca), and (4-tfmptp)(2)Ir(3-iqca). These complexes feature the rigid 4-tfmptp (4-[4-(trifluoromethyl)phenyl]thieno[2,3-d]pyrimidine) as the primary ligand, with pic (picolinic acid), 3-ppca (pyrrolo[1,2-c]pyrimidine-3-carboxylic acid), and 3-iqca (isoquinoline-3-carboxylic acid) as the auxiliary ligands, respectively. In comparison to the complex (4-tfmptp)(2)Ir(pic) based on the classic auxiliary ligand pic, the emission peaks of (4-tfmptp)(2)Ir(3-ppca) and (4-tfmptp)(2)Ir(3-iqca) remain largely unchanged, at around 568 nm. However, their photoluminescence quantum yields (PLQYs) in CH2Cl2 improve remarkably, increasing from 53.6% to 93.6% and 97.2%, respectively. Furthermore, solution-processed OLEDs based on (4-tfmptp)(2)Ir(3-ppca) and (4-tfmptp)(2)Ir(3-iqca) exhibited exceptional device performances, with maximum current efficiencies of 74.2 and 91.4 cd A(-1), and maximum external quantum efficiencies (EQE(max)) of 27.8% and 31.4%, respectively. These results suggest the modification of auxiliary ligand can affect the photophysical properties of the Ir(III) complexes greatly.