Efficiency Enhancement in Polymer Light-Emitting Devices Fabricated Utilizing a MoO3 Hole Injection Layer Coated with Different Solvents.

Polymer light-emitting devices (PLEDs) with a MoO3 hole injection layer (HIL) were fabricated to enhance their luminance efficiency. Ultraviolet photoelectron spectroscopy spectra showed that the valence band maximum level of the MoO3 layer was located between the work function of the the indium-tin-oxide anode and the highest occupied molecular orbital level of the poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine] hole transport layer. The surface of the MoO3 layer formed by using an ethanol solvent was smoother than that of the MoO layer formed by using a deionized water solvent due to a decrease in the aggregation of the MoO3 resolved in ethanol. The MO3 HIL decreased the operating voltage of the PLED and increased the luminance and the luminance efficiency of the PLED due to a decrease in the hole injection barrier. The operating voltage, the luminance, and the luminance efficiency of the PLEDs with the MoO3 HIL formed by using an ethanol solvent were enhanced in comparison with those of the PLEDs with a MoO3 HIL formed by using a deionized water solvent due to a decrease in the surface roughness of the HIL.