Efficient Narrowband Yellow Organic Light-Emitting Diodes Based on Iridium(iii) Complexes with the Rigid Indolo[3,2,1-Jk]carbazole Unit

Phosphorescent material with narrowband emission is crucial for advancing wide-color-gamut organic light-emitting diodes (OLEDs). In this work, two iridium(iii) complexes, (PhthzICz)2Ir(tmd) and (thzICz)2Ir(tmd), using rigid 2-(benzothiazole-2-yl)indolo[3,2,1-jk]carbazole (PhthzICz) and 2-(thiazole-2-yl)indolo[3,2,1-jk]carbazole (thzICz) as cyclometalated ligands and 2,2,6,6-tetramethyl-3,5-heptanedione (tmd) as ancillary ligands, were synthesized. When these complexes were doped into the host material 3,3 '-di(9H-carbazol-9-yl)-1,1 '-biphenyl, the doped films exhibited yellow photoluminescence (PL) peaking at 537 and 531 nm, full width at half maximum (FWHM) bands of 35 and 60 nm, and PL quantum yields of 89.9% and 85.9%, respectively. OLEDs based on these two emitters display moderate performance characteristics with maximum external quantum efficiencies of 25.2% and 22.7%. Notably, the device based on (PhthzICz)2Ir(tmd) exhibits a narrow FWHM of 31 nm. Overall, the study highlights the practicality of incorporating rigid groups into the cyclometalated ligands of Ir(iii) complexes as a viable strategy for achieving efficient Ir(iii) complexes for OLEDs with narrow emission and high efficiency.