High-performance solution-processed orange phosphorescent OLEDs based on rigid 4-tfmptp iridium(III) complexes with modified auxiliary ligands
Phosphorescent iridium(III) complexes are pivotal for high-efficiency organic light-emitting diodes (OLEDs), yet solution-processable systems with high photoluminescence quantum yields (PLQYs) and balanced charge transport remain scarce. This study reports three orange-emitting Ir(III) complexes, (4-tfmptp)2Ir(pic), (4-tfmptp)2Ir(3-ppca), and (4-tfmptp)2Ir(3-iqca), employing the rigid 4-tfmptp (4-[4-(trifluoromethyl)phenyl]thieno[2,3-d]pyrimidine) as the primary ligand and picolinic acid (pic), pyrrolo[1,2-c]pyrimidine-3-carboxylic acid (3-ppca), or isoquinoline-3-carboxylic acid (3-iqca) as auxiliary ligands. While emission peaks remain at approximately 568 nm, the PLQYs in CH2Cl2 increase dramatically from 53.6% for the pic-based complex to 93.6% and 97.2% for the 3-ppca and 3-iqca analogues, respectively. Solution-processed OLEDs fabricated with these emitters achieve maximum current efficiencies of 74.2 cd A−1 and 91.4 cd A−1, and maximum external quantum efficiencies (EQEmax) of 27.8% and 31.4% for the 3-ppca and 3-iqca devices, respectively. These results demonstrate that auxiliary ligand modification substantially enhances the photophysical properties of Ir(III) complexes, enabling high-performance solution-processed phosphorescent OLEDs.