The efficiency of the organic light emitting diode (OLED) can be remarkably improved by introducing a hole injection layer (HIL) between the anode and the active layer. Typical examples of TMD are MoS2, WS2, and TiS2. Applying TMD can increase efficiency, but it will also improve efficiency by applying graphite oxide (GO) together. TMD nanosheets are manufactured by the exfoliation method using ultrasonic treatment, and GO is synthesized by the modified Hummers method. TMD nanosheets are synthesized to thicknesses and sizes of about 3.1-4.3 nm and over 100 nm, and GO is synthesized at 400 nm to several micrometers. The large-sized GO can completely cover the surface of the indium tin oxide (ITO) film to reduce the roughness. OLEDs with GO HIL show very high highest maximum power efficiency (PEmax) due to very low roughness. These results indicate that the TMD-GO composites are applied to the HIL layer in OLEDs and show high efficiency.
This research was supported in part by National Research Foundation of Korea (NRF) grants provided by the Korean government (MSIP) (Nos 2015K1A3A1A59073839, 2017H1D8A1030599, 2017K1A3A1A67014432) and in part by Korea Agency for Infrastructure Technology Advancement grant funded by Ministry of Land, Infrastructure and Transport (17IFIP-B133622-01).