Continuous and Extremely Flat Ag Electrode by Tailoring Surface Energy for Organic Light-Emitting Diodes

Abstract

The exploration of alternative transparent electrodes to indium tin oxide (ITO) in organic light-emitting diodes (OLEDs) has been a topic of interest. Among various candidates, ultrathin and continuous metal films have garnered significant interest for their ability to offer both transparency and conductivity. However, due to the higher surface energy of metals compared to substrates, metal films tend to grow in a discrete island shape, resulting in poor conductivity and even low transparency due to a localized surface plasmon by metal islands. In this work, a way to produce homogeneous ultrathin and continuous Ag film (UCAF) achieved through primary NF₃ plasma treatment on a glass substrate is proposed. This treatment introduces F bonds on the surface, enhancing the hydrophilicity of the glass surface and facilitating the formation of UCAF with high optical transmittance (>70%) and low sheet resistance (<10 Ω/ϒ). By incorporating UCAF into OLEDs as a bottom electrode, the current efficiency showed an 86% enhancement compared to an ITO bottom electrode at an operating current density of 10 mA cm⁻². Numerical simulation results elucidated superior light extraction efficiency in OLED with UCAF compared to that with ITO, attributed to both cavity effect and reduced waveguide mode at the organic/electrode interface.