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)2Ir(acac) and (3OMePhbt)2Ir(acac), have been synthesized. Compared with their parent compound (bt)2Ir(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)2Ir(acac) bearing para-phenyl possesses worse processability relative to (bt)2Ir(acac) due to spontaneous crystallization stemming from the intense intermolecular interactions. Single-layer solution-processed PhOLEDs with (3Phbt)2Ir(acac) and (3OMePhbt)2Ir(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)2Ir(acac) (10.2 cd A(-1) and 14,350 cd m(-2)) and (4Phbt)2Ir(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.