Blue phosphorescent organic light-emitting diodes with extended operational lifetime through hole transport layer management

Abstract

Achieving higher efficiency and a longer operational lifetime is equally important yet remains a daunting task in the domain of blue phosphorescent organic light-emitting diodes (PhOLEDs). Optimizing an appropriate hole transport layer (HTL) has proven to be a potential approach for improving the performance of blue PhOLED. In the present work, we investigated a spiro-bifluorene-based SFAF HTL to develop blue PhOLEDs with high efficiency and extended operational lifetime. The spiro-bifluorene unit imparts enhanced thermal stability to the SFAF molecular structure. Further, careful management of the thickness of SFAF HTL fosters a charge balance in the emitting layer and subsequently strengthens the performance of the fabricated devices. The fabricated devices emit in the blue region, achieving an EQE_max nearing 20 %, and demonstrated excellent resistance to efficiency roll-off at higher luminance. Interestingly, the operational lifetime up to 95 % of the initial luminance (LT₉₅) of the SFAF devices measured at 1000 cd/m² brightness was more than double compared to that of the reference device fabricated using BCFN as HTL, which has a structure similar to the SFAF without the spiro group. The study suggests that the spiro-bifluorene-based HTLs can be excellent candidates for developing blue phosphorescent OLEDs with higher efficiency and longer operational lifetime.