A deep blue TADF dendron for efficient energy transfer in green and red iridium light emitting dendrimers

Abstract

Light-emitting dendrimers are promising materials for solution-processed large area organic light-emitting diodes (OLEDs). The dendron design critically influences both luminescence efficiency and charge transport properties. Here, we report two new phosphorescent dendrimers, DB-G and DB-R, in which a deep-blue emissive thermally activated delayed fluorescence (TADF) dendron, 2,6-bis[3,6-bis(2-ethylhexyl)-9H-carbazol-9-yl]benzonitrile (DB), is covalently attached to each ligand of green-emitting fac-tris(2-phenylpyridyl)iridium(III) [Ir(ppy)₃] and red-emitting fac-tris[2-(thiophen-2-yl)-4-phenylquinoline]iridium(III) [TQIr] cores. The dendrimers had core-based phosphorescent emission with solution photoluminescence quantum yields (PLQYs) of 85% (DB-G) and 78% (DB-R). Neat films also showed emission exclusively from the core with the PLQYs being 40% and 35% for DB-G and DB-R, respectively. OLEDs composed of neat DB-G and DB-R emissive layers showed maximum external quantum efficiencies (EQEs) of 12% and 4.8%, respectively, with the DB-G-based devices benefiting from electron transport through both the dendrons and core. Blending the dendrimers into tris(4-carbazoyl-9-ylphenyl)amine significantly improved the device performance, with peak EQEs of 15.8% for the green-emitting DB-G and 13.9% for the red-emitting DB-R at 1 mol% loading.