Ag:MoO3:Yb semi-transparent electrode for top emission organic light-emitting didoes

초록

Silver (Ag) is widely used as a cathode in top-emission organic light-emitting diodes (TEOLEDs) for its high reflectivity and conductivity. However, its high absorption, thickness-dependent transmittance, and high work function require further improvement. While Ag:MoO3 alloy has emerged as an alternative, it still needs further enhancement. In this study, we developed a ternary Ag:MoO3:Yb semi-transparent electrode, improving both the optical and electrical properties of the existing binary system. For example, The 30 nm-thick Ag:MoO3:Yb 4:3:3 film exhibited average transmittance, reflectance, and absorption of 64 %, 12 %, and 24 %, respectively. Additionally, the Ag:MoO3:Yb showed a uniform transmittance spectrum in the visible wavelength range. The photoelectron spectroscopy results showed Ag:MoO3:Yb 4:3:3 film has a low work function of 3.69 eV. Despite relatively high sheet resistance around 82-130 Omega/sq, the red phosphorescence TEOLEDs incorporating Ag:MoO3: Yb as cathode showed improved device performances compared to the control device with Ag:MoO3 30 % where the current efficiency increased by up to 1.7 times and the power efficiency by up to 2.6 times. Furthermore, the optimized Ag:MoO3:Yb devices with good charge balance resulted in a relatively longer lifetime up to 80 % of initial luminance (LT80) of 166 hr, which are higher performance than those of the device with Ag:MoO3 30 %.

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