Effect of self-assembled monolayer on electroluminescence properties of organic light-emitting diodes

We investigate the effect of a self-assembled monolayer (SAM) as a hole injection layer on the electroluminescence (EL) properties of organic light-emitting diodes (OLEDs). We modify the surface of an indium-tin-oxide (ITO) substrate using (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane (F-SAM) and n-decyltriethoxysilane (CH3-SAM). The current of the OLED with F-SAM is higher that those of the OLEDs with or without CH3-SAM at the same voltage and the same as that of an OLED with copper phthalocyanine (CuPc). In addition, the half-lifetime of the OLED with F-SAM is 2500 times greater than that of the OLED without the hole injection layer and about twice that of the OLED with CuPc. We discuss the conduction mechanism of the OLED in terms of the barrier height of the hole injection and the voltage distribution of the organic layers.