Enhancing OLED Performance by Optimizing the Hole Transport Layer with a Self-Assembled Monolayer

The enhancement of organic light-emitting diode (OLED) device performance has been a key area of research in organic optoelectronic devices. Optimizing carrier mobility within OLED devices is a crucial strategy. In this study, the hole transport layer was optimized using a self-assembled monolayer (SAM) subjected to different annealing temperatures. Through submitting the SAM to an annealing temperature of 100 °C, a maximum luminous intensity of 32,290 cd/m² and a maximum EQE of 1.77 were achieved, the latter being more than two-fold higher than that without the SAM. As the SAM annealing temperature increased from 80 °C to 120 °C, both the vertical orientation of molecules in the hole transport layer and the hole mobility in hole-only devices (HODs) improved. This vertical orientation is beneficial to enhancing hole mobility. Electrochemical impedance spectroscopy and surface morphology analysis revealed that the introduction of a SAM leads to the formation of interface resistance. The synergy effect between the variation in the molecular transition dipole moment and the interface morphology of the hole transport layer optimizes the hole mobility of HODs and leads to the enhancement of OLED performance.