ZnO/Ag/ZnO multilayers as an n-type transparent conducting electrode for transparent organic light-emitting diodes
Sneha Sreekumar, Vladimir V. Bruevich, Vitaly Podzorov, Deirdre M. O’Carroll
Abstract
Alternative transparent conducting electrodes (TCEs) have gained significant attention in recent decades in an effort to replace costly indium-tin oxide (ITO) in organic optoelectronic devices. For example, state-of-the-art top-emitting, transparent organic light-emitting diodes (OLEDs) in the display industry require a transparent or semi-transparent cathode for electron injection. The current OLED display technology employs ultrathin metallic (typically Mg:Ag) layers as semitransparent cathodes. However, recent studies have shown that metal oxide/metal/meta-oxide multiplayers can perform better optically and offer improved stability compared to semitransparent metal cathodes. Yet, deposition of these multilayers with minimal damage to the underlying organic emissive layer is imperative. Here, we investigate the ZnO/Ag/ZnO TCE system deposited under mild sputtering conditions that are safe for the emissive layer. We demonstrate ∼ 85 % transparent electrodes with a sheet resistance of 1.47 Ω/□, which is more conductive than the industry standard, ITO. We also integrated such a multilayer electrode in a transparent OLED device built on ITO, demonstrating the compatibility of this TCE with the existing OLED technology.