Tb(acac)3(phen-Cl) was utilized as sensitizer for the first time in phosphorescent OLEDs.
Tb(acac)3(phen-Cl) exhibited low-lying energy levels and high triplet energy of ligand.
No Tb(III) ion emission was observed in co-doped devices.
Tb(acac)3(phen-Cl) co-doped devices obtained higher brightness, higher efficiencies and even slower efficiency roll-off.