[en] Graphical abstract: Our experimental results revealed the combination of 3 nm MoO₃ layer and 2 min low pressure nitrogen plasma treatment at 4000 V m⁻¹ is most efficient in depressing the unexpected leakage current without sacrificing the injection rate of holes. - Highlights: • Improved hole injection modified by MoO₃ layer and low pressure plasma. • Higher surface roughness would decrease the injection of holes. • Unexpected leakage current could be depressed by low pressure plasma treatment. • Provide helpful information for the optimization on structure design of OLEDs. - Abstract: In this work, we performed the investigation on surface modification of indium tin oxide (ITO) anode by depositing MoO₃ interface layer and treating with low pressure plasma. Experimental results revealed both low pressure oxygen plasma treatment and MoO₃ interface layer are efficient in facilitating the injection of holes, while both modifications increase the ITO surface roughness. Interestingly, the electroluminescent (EL) device with 3 nm MoO₃ layer displayed the highest EL performances, which were even higher than those of the device with both modifications. By optimizing the selection of gas, treatment time, and applied electric field intensity of low pressure plasma treatment, the combination of 3 nm MoO₃ layer and 2 min low pressure nitrogen plasma treatment at 4000 V m⁻¹ was demonstrated to be most efficient in depressing the unexpected leakage current without sacrificing the injection rate of holes.