In this paper, graphene oxide is used instead of poly (3,4-ethylenedioxythiophene): poly (phenylethylenesulfonic acid) PEDOT:PSS as the hole injection layer of quantum dot light-emitting diodes. The experimental results prove that graphene oxide irradiated with ultraviolet for an appropriate time can improve the performance of the device. Compared with traditional devices, the luminance is increased by 1.9 times and current efficiency of the device is increased 2.4 times. In addition, the turn-on voltage was reduced from 2.8 V to 2.4 V. The improvement of these photoelectric properties is mainly due to the fact that graphene oxide after ultraviolet irradiation can form a good energy level structure with the anode and the hole transport layer, which is more conducive to hole injection.

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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)