Novel Ir(III) complexes ligated with 2-(2,6-difluoropyridin-3-yl)benzo[d]thiazole for highly efficient OLEDs with mild efficiency roll-off

Abstract

2-phenylbenzothiazole-based Ir(III) complex [(bt)2Ir(acac)] is a class of typical yellow phosphorescence material, which has been widely used in OLEDs. However, (bt)2Ir(acac) exhibited only mild photoluminescence quantum efficiency (PLQY) of 0.26–0.28. To further improve the luminous efficiency of benzothiazole-based Ir(III) complex and then boost the corresponding electroluminescent performance, (fpbt)2Ir(pic) and (fpbt)2Ir(tftp) were successfully synthesized, where 2-(2,6-difluoropyridin-3-yl)benzo[d]thiazole (fpbt) was applied as C∩N main ligand, and 2-pyridine carboxylic acid (pic), 2-(3-(trifluoromethyl)-1H-1,2,4-triazol-5-yl)pyridine (tftp) acted as different auxiliary ligands. Both (fpbt)2Ir(pic) and (fpbt)2Ir(tftp) presented excellent PLQYs (0.93–0.95) and high thermostability (330–360 °C). The vacuum-deposited devices following the architecture of ITO/TAPC/CBP: dopant/TPBi/Liq/Al demonstrated prominent performances. Of them, (fpbt)2Ir(pic)-doped OLEDs exhibited better efficiencies of 20.6%, 68.8 cd A−1, and 40.8 l m W−1 while maintaining very mild efficiency roll-off. Such outstanding electrophosphorescent performances were further investigated, which was probably attributed to the following factors: 1) high PLQY; 2) good electron mobility; 3) uniform film-forming property.