E-beam deposited ultra-smooth silver thin film on glass with different nucleation layers: An optimization study for OLED micro-cavity application

A study on the optimization of a thin (25 nm) silver film deposited by e-beam on glass substrate has been performed in order to achieve a smooth, spike-free, mechanical resistant and semi-transparent electrical conducting layer to be used as anode of a blue bottom emitting organic light-emitting diode (OLED) micro-cavity. To improve the flattening of asperities, rough grains and spikes, that can induce short circuit in the OLEDs, as well as the mechanical adherence of the thin silver film on a cleaned borosilicate glass, different thin nucleation layers (such as Cr, Ge and a-C:H) have been built and tested. Both the nucleation layers as well as the silver films have been grown at different deposition rates. A thin (40 nm) poly(3,4-ethyl-enedioxythiophene)/polystyrene-sulphonate (PEDOT-PSS) layer has been deposited by spin-coating on the different bi-layer anodes to improve the hole injection into the OLED hole transport layer. The surface morphology of the silver thin films with and without PEDOT-PSS layer has been studied using a field emission gun scanning electron microscope (FEG-SEM) and a high resolution optical profiler. The optimized silver anode obtained using a 5 nm Ge nucleation layer and a high silver deposition rate (1.1 nm/s) has been successfully used to obtain a long lifetime, large area and short circuit free bottom micro-cavity OLED.