Investigation of time-dependent UV-ozone treatment on an ultra-thin AgF buffer layer for organic light-emitting diodes

The effect of ultraviolet (UV)-ozone treatment on an ultrathin AgF buffer layer deposited on indium tin oxide (ITO) substrate was studied for various layer thicknesses and treatment times. Work function was estimated from X-ray photoelectron spectroscopy, and surface properties were calculated from measured contact angles using H ₂O and CH ₂I ₂ as test liquids. With improper UV-ozone treating times, no luminance was induced by current at a low voltage due to the resonant tunneling effect or a damaged film surface. However, the surface energy, surface polarity and work function were increased by proper treatment of the ultra-thin AgF film, and the resonant tunneling effect was simultaneously eliminated, resulting in improvement in device performance. An optimal thickness AgF (2 nm) with proper UV-ozone treatment time (1 min) significantly improved device performance (ITO/AgF/NPB/Alq ₃LiF/Al). Our results indicate that the device efficiency of OLEDs can be greatly enhanced by simultaneous control of AgF film thickness and UV-ozone exposure time.