Study on highly efficient graphene-based solution processed PLEDs through charge balance

Abstract

In this study, molybdenum oxide nanoparticles were synthesized and utilized in order to enhance the performance of the graphene anode and the polymer light-emitting diodes. The electrical and optical characteristics of $MoO_x$-doped graphene anode were analyzed to understand the role of $MoO_x$ on graphene anode. Also, J-V-L curve and hole-only device (HOD) were characterized to figure out the enhanced performance of PLEDs using $MoO_x$-doped graphene anode. From ultraviolet photoelectron spectroscopy (UPS) analysis, it was revealed that the hole injection barrier was reduced which resulted in enhanced device performance. In order to further improve the performance, modified stacking structure was introduced. Moreover, $MoO_x$ was hybridized with graphene oxide (GO) to replace conventional hole transporting layer (HTL), PEDOT:PSS and also to act as p-type dopant for graphene anode. X-ray photoelectron spectroscopy (XPS) was facilitated to understand the phenomena behind the hybridization of graphene oxide/$MoO_x$ (GOMO) material. It was observed that GO was partly reduced and oxygen vacancy of $MoO_x$ was removed. As a result, hole conductivity of the PLED using GOMO as HTL was increased. The device performance was comparable to PEDOT:PSS-based PLED indicating that GOMO can be applied as HTL and simultaneous p-type dopant for graphene anode. Finally, intense pulsed light (IPL) using xenon flash lamp was treated on GOMO thin-film to develop a more enhanced performance. Oxygen-containing functional groups of GO was markedly eliminated and the workfunction of GOMO was increased by 0.4 eV with IPL treatment. Consequently, a better charge balance was obtained and a highly efficient PLED was demonstrated with IPL-treated GOMO as the HTL.