Optimizing hole-injection in organic electroluminescent devices by modifying CuPc/NPB interface

This investigation discusses the performance of an organic light-emitting device (OLED) with ultraviolet (UV) illuminated and remote pulsed Ar plasma (RPAP), treated copper phthalcyanine (CuPc) thin film on an indium tin oxide anode as the hole-blocking layer. UV treatment increased the driving voltage, the current efficiency decreased at the same time due to the poor sticking probability of NPB on the CuPc surface. By contrast, the driving voltage reduction and current efficiency enhancement were achieved at the same time for the OLED with the RPAP treated CuPc. Besides this, in such device, the thickness of CuPc affects seldom the current density–voltage–luminance characteristics. The surface characteristics of these processed CuPc thin films were investigated by using atomic force microscope, contact angle and X-ray photoelectron spectroscopy measurements, which showed the CuPc/, N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) interface was crucial to not only the interface energy barrier, but also the following NPB growth, mode.