Blended hole-transport layer for efficient and stable full-color NiOx-based QLEDs

Abstract

Highly stable inorganic metal oxide-based hole-injection materials demonstrate significant potential for advancing the commercialization of quantum dot light-emitting diodes (QLEDs). However, the performance of NiO_x-based QLEDs necessitates further enhancement owing to their inferior hole-injection ability. In this work, a novel blended hole-transport layer (HTL) was developed to improve charge injection in NiO_x-based QLEDs. Specifically, the high hole mobility of poly((9,9-dioctylfluorenyl-2,7-diyl)-alt(4,4′-(N-(4-butylphenyl)))) (TFB) facilitates hole transfer, while the shallow lowest unoccupied molecular orbital of poly((9,9-dioctylfluorenyl-2,7-diyl)-alt-(9-(2-ethylhexyl)-carbazole-3,6-diyl)) (PF8Cz) suppresses electron leakage. As a result, the full-color NiO_x-based QLEDs with TFB@PF8Cz HTL exhibited current efficiencies of 21.31 (red), 23.17 (green), and 0.81 cd A⁻¹ (blue), corresponding to 43.5% (89.1%), 26.1% (41.5%) and 22.7% (113.2%) enhancements, respectively, compared to those of devices with TFB HTL (PF8Cz HTL). It is worth noting that TFB@PF8Cz QLED demonstrated exceptional operational stability. The luminance decreased to approximately 50% of the initial level (1000 cd m⁻²) after 55 hours of continuous operation and after being operated continuously for 600 hours, while the operating voltage increased only slightly by 0.15 V. This work provides a simple and efficient method for modifying the charge injection of NiO_x-based QLEDs.