Highly efficient hole injection/transport layer-free OLEDs based on self-assembled monolayer modified ITO by solution-process

摘要

Hole injection/transport layer-free organic light-emitting diodes (HIL/HTL-free OLEDs) are highly anticipated due to their simpler fabrication process,lower material cost and no interlayer intermixing in solution-processed OLEDs.This study presents a comprehensive strategy to obtain HIL/HTL-free OLEDs.Here,indium tin oxide (ITO) was modified by self-assembled monolayer (SAM) of various phosphoric acids (PAs).The effect of work function,PA content and PA conductivity on the hole injection from the modified ITOs was systematically studied,it was found that PA conductivity plays a decisive role.By comparation,it was revealed that pentafluorobenzyl phosphonic acid modified ITO (F_5BnPA-ITO) could provide the highest hole injection.Moreover,exciton quenching near the ITO was effectively suppressed by F5BnPA SAM together with adjusting device structure.Resultantly,solution-processed phosphorescent OLEDs based on F_5BnPA-ITO achieved a maximum power efficiency of 63.13 lm W~(-1) and preferable current efficiency of 60.32 cd A~(-1),which is the state-of-the-art among the reported solution-processed OLEDs with similar emitters.This contribution is the first to report that HIL/HTL-free OLEDs achieved preferable performance than standard multilayered devices.