Characterization of hydrogen-free diamond-like carbon film on COC for flexible organic electro-luminescence application

The applicability of the top emission organic light-emitting diode (TEOLED) with multilayer electrodes on flexible cyclic olefin polymers (COC) substrates depends on an ultra smooth, low-transmittance, insulating substrate overcoat to support the device structure. In this study, the feasibility of the diamond-like carbon (DLC) film as a viable device component for TEOLED was investigated. Featured for its advanced physical and chemical advantages such as high hardness, chemical stability, and wide band-gap optical transparency, the hydrogen-free DLC exhibits promising characteristics as the flexible substrate and TFT component overcoat. Ultra smooth and hydrogen-free DLC thin films were synthesized by using filter arc deposition (FAD) system. Raman spectroscopy, ESCA, Nano-Indenter, and electron microscopy were used to characterize the electronic, morphological, and microstructure properties of the DLC coatings. Results indicate that the device-quality DLC needs to be synthesized at lower substrate bias potential to retain a higher sp3/sp2 ratio. The bending tests demonstrated a 30-fold improvement of the DLC protected COC over that of the unprotected COC. The water vapor permeability tests demonstrated a 25-fold improvement of the DLC protected COC over that of the unprotected COC. The configuration of TEOLED was made of Al/Au/NPB/Alq3/LiF/Al/Ag to realize the top emission device, which was assembled with conventional thermal evaporation process. The design of the COC substrate/DLC/Al/Au/NPB/Alq3/LiF/Al/Ag of TEOLED device is shown optimized to reach the emission efficiency of 1–3 cd/A and luminance intensity of 1800 cd/m2 at 18 V.