Symmetrical Emission Transparent Organic Light-Emitting Diodes With Ultrathin Ag Electrodes

Abstract

This paper describes a way to implement a transparent electrode for symmetrical emission from the bottom and top sides of transparent organic light-emitting diodes (TOLEDs). An ultrathin (∼6 nm) and smooth Ag film was achieved by using the pretreatment of using oxygen plasma prior to deposition of a nanoscale-thin Ag film on glass. The treatment increased the surface energy, thereby enhancing the wettability of the Ag on glass substrate and consequently leading to the formation of thin and unifrom Ag film with high optical transmittance T ∼ 76% and low sheet resistance RS < 15 Ω □-1. Using this scheme, a highly transparent glass/Ag/WO3 structure with T = 85.6%, and RS = 9.3 Ω □-1 was designed (ITO: 83.1%, 10 Ω □-1). We conducted finite-domain time-difference simulation for this glass/Ag/WO3 electrode to design a weak microcavity structure that retained the transparency and emitting properties. This optimized structure of TOLEDs (Ag = 6 nm) showed higher T = 73.84% than those of ITO devices (T = 73.19%), and can induce the weak microcavity effect, resuting in improved electroluminescent properties and increased the luminance value from 38.25 to 56.25 cd A-1 at 25 mA cm-2.