Solution-Processable MoO_x for Efficient Light-Emitting Diodes Based on Giant Quantum Dots

We report efficient quantum dot light-emitting diodes (QLEDs) using sizable 13-nm green-emission quantum dots as the emissive layer and solution-processable MoO_x as the hole injection layer (HIL). The MoO_x HIL was prepared by the decomposition of a solution of ammonium molybdate tetrahydrate at 80 °C under ambient conditions, further spin-coated onto an indium tin oxide substrate to facilitate hole injection. Compared with the reference sample with a polymeric hole injection material poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), the sMoO_x film showed a higher work function of 5.6 eV, better transparency, and smoother surface morphology. The stable QLED with optimized MoO_x film thickness achieved a higher maximum current efficiency of 10.8 cd/A at a lower turn-on voltage of 2.2 V versus the one with a PEDOT:PSS HIL, 9.9 cd/A and 2.9 V, respectively. Moreover, a small leakage current in sMoO_x-device was found, which was attributed to the better surface morphology of sMoO_x.