Novel spiro[fluorene-9,9′-xanthene]-based hole transport layers for red and green PHOLED devices with high efficiency and low efficiency roll-off

Abstract

Two N-phenyl-1-naphthylamine (PNA)/spiro[fluorene-9,9′-xanthene] (SFX) hybrid materials (DPNA-SFX and DOPNA-SFX) were successfully obtained by incorporating two PNA groups with a bridging phenyl ring to an SFX center. Both materials possess similar photophysical properties and an outstanding glass-transition temperature (T_g) beyond 150 °C surpassing that of most typical spirobifluorene and SFX materials. Both green and red phosphorescent organic light-emitting diodes (PHOLEDs) based on two materials achieved remarkable results. The DPNA-based green devices exhibited decent performance with the maximum current efficiency (CE_max), power efficiency (PE_max) and external efficiency (EQE_max) of 89.8 cd A⁻¹, 94.2 lm W⁻¹ and 24.7%, respectively. More importantly, the pure red PHOLEDs with DPNA-SFX as the hole-transporting material achieved the CE_max, PE_max and EQE_max of 41.1 cd A⁻¹, 46.4 lm W⁻¹ and 34.7%, respectively, which is comparable to those of the best red PHOLEDs. And the EQE at 1000 cd m⁻² maintained 96% of its peak value, demonstrating an extremely low efficiency roll-off.