Enhancing Hole Transport of Quantum‐Dot Light‐Emitting Diodes by a Cruciform Oligothiophene for Effective p‐Type Doping

Abstract

Effective p-type doping is essential to enhance hole transport and balance electron-hole injection in quantum dot light-emitting diodes (QLEDs). Here, an oligothiophene material is adopted as a p-type dopant in the hole-transport layer, considering its cruciform cross-center structure, precise molecular weight, and high purity. Compared with the dopant-free counterpart, hole transport capability at the optimal doping level exhibits a significant improvement, producing a boosted external quantum efficiency (EQE) and luminance up to 20.8%, 213 439 cd m -2 , respectively, among the highest reported on the red-light emission. The work indicates the potential applications of oligothiophene material in red light-emitting devices. IntroductionQuantum dot light-emitting diodes (QLEDs), with unique physical properties such as tunable emission wavelength, light stability, and high color purity, have gained extensive research interests in the next generation of display and lighting devices in recent years. [1][2][3][4][5][6][7][8] Generally, the QLED device has a hybrid structure consisting of an organic hole-transport layer (HTL) and a metal oxide-based electron-transporting layer (ETL). However, compared with electron mobility (10 cm 2 V -1 s -1 ) in the ETL, the relatively low hole mobility (10 -3 cm 2 V -1 s -1 ) in the organic materials like poly(9,9-dioctylfluorene-co-N-(4-(3methylpropyl))diphenylamine) (TFB) and poly (9-vinylcarbazole)