Low-temperature solution-processed MoOx as hole injection layer for efficient quantum dot light-emitting diodes

Abstract

In this work, quantum dot light-emitting diodes (QD-LEDs) based on a low-temperature solution-processed MoO_x hole injection layer were fabricated. As a result of the excellent wettability of the MoO_x precursor, a smooth sMoO_x HIL film with a roughness of less than 1 nm was obtained. In comparison with a device based on PEDOT:PSS, the best sMoO_x-based QD-LED displayed comparable device performance in terms of a maximum luminance of 10 225 cd m⁻², a peak current efficiency of 4.04 cd A⁻¹, a maximum external quantum efficiency of 1.61% and, more importantly, an approximately threefold increase in operational lifetime. Furthermore, we investigated the relationship between the thermal treatment of the sMoO_x film and the device performance. UPS measurements revealed that the work function of the sMoO_x film underwent an upshift from 5.51 to 4.90 eV when the annealing temperature was increased from 50 to 250 °C, which indicated that low-temperature treatment of the sMoO_x HIL is beneficial for hole injection and EL performance. This demonstration of a bright, efficient and stable sMoO_x-based QD-LED provides another feasible application of solution-processable transition metal oxide materials as the HIL within QD-LEDs and promotes the development of low-cost, all-solution-processed optoelectronic devices.