Effects of diamond-like carbon in TPD-Alq3 doped PVK organic light-emitting devices

Effects of an ultrathin (~ 1 nm) diamond-like carbon (DLC) layer in single-layer organic light-emitting devices (OLEDs) that consist of ITO/(TPD-Alq3 doped PVK)/Al were investigated. DLC layers deposited by using Nd:YAG laser at laser wavelengths of 355 nm were high in sp3 content and resistivity (DLCUV) while that of 1064 nm laser were lower in sp3 content and resistivity (DLCIR), as characterized by Raman spectroscopy and resistivity measurements. Although emission were obtained for all the devices, only the device of ITO/DLCUV/(TPD-Alq3 doped PVK)/Al exhibited enhanced current density and brightness with lower turn-on voltage as compared to a standard device. Devices of ITO/DLCIR/(TPD-Alq3 doped PVK)/Al and ITO/(TPD-Alq3 doped PVK)/DLCUV/Al showed poor current and brightness characteristics but failed at higher applied voltage. The enhance performance of device with high resistivity/sp3 DLC film suggests the mechanisms of barrier reduction by sufficiently thin insulating layer which increase the probability of tunneling of carriers at ITO and PVK interface.