Iridium(iii) complexes with enhanced film amorphism as guests for efficient orange solution-processed single-layer PhOLEDs with low efficiency roll-off

Abstract

By introducing a phenyl substituent into the meta-site of the phenyl segment of the 2-phenylbenzothiazole ligand, two novel orange iridium(III) complexes, namely, (3Phbt)₂22Ir(acac) and (3OMePhbt)₂22Ir(acac), have been synthesized. Compared with their parent compound (bt)₂22Ir(acac), both of them possess much enhanced thermostability and film amorphism, making them suitable candidates as guests for high performance solution-processed phosphorescent organic light-emitting diodes (PhOLEDs). However, (4Phbt)₂22Ir(acac) bearing para-phenyl possesses worse processability relative to (bt)₂22Ir(acac) due to spontaneous crystallization stemming from the intense intermolecular interactions. Single-layer solution-processed PhOLEDs with (3Phbt)₂22Ir(acac) and (3OMePhbt)₂22Ir(acac) as guests show peak current efficiency of 17.2 cd A⁻¹ and 15.2 cd A⁻¹, and maximum brightness of 28 270 cd m⁻² and 27 900 cd m⁻², respectively. Both are greatly improved compared to the devices employing (bt)₂22Ir(acac) (10.2 cd A⁻¹ and 14 350 cd m⁻²) and (4Phbt)₂22Ir(acac) (5.0 cd A⁻¹ and 13 790 cd m⁻²) as phosphors. Moreover, quite low efficiency roll-off is acquired in these devices at high luminance. The much improved electroluminescence performances of these objective complexes could be mainly attributed to the presence of a rigid phenyl on the appropriate substitution site of the cyclometallate ligand, which leads to improved thermostability with compatible alleviated intermolecular interactions, and consequently enhanced film amorphism.