MoS2-nanosheet/graphene-oxide composite hole injection layer in organic light-emitting diodes

In this work, composite layers comprising two-dimensional MoS 2 and graphene oxide (GO) were employed as hole injection layers (HILs) in organic light-emitting diodes (OLEDs). MoS 2 was fabricated by the butyllithium (BuLi) intercalation method, while GO was synthesized by a modified Hummers method. The X-ray diffraction patterns showed that the intensity of the MoS 2 (002) peak at 14.15° decreased with increase in GO content; the GO (001) peak was observed at 10.07°. In the C 1s synchrotron radiation photoemission spectra, the contributions of the C-O, C=O, and O-C=O components increased with increase in GO content. These results indicated that GO was well mixed with MoS 2 . The lateral size of MoS 2 spanned from a few hundreds of nanometers to 1 μm, while the size of GO was between 400 nm and a few micrometers. Thus, the coverage of the MoS 2 -GO composite on the ITO surface improved as the GO content increased, owing to the large particle size of GO. Notably, GO with large size could fully cover the indium tin oxide film surface, thus, lowering the roughness. The highest maximum power efficiency (PE max ) was exhibited by the OLED with MoS 2 -GO 6:4 composite HIL, indicating that similar contents of MoS 2 and GO in MoS 2 -GO composites provide the best results. The OLED with GO HIL showed very high PE max (4.94 lm W −1 ) because of very high surface coverage and high work function of GO. These results indicate that the MoS 2 -GO composites can be used to fabricate HILs in OLEDs.