Bulk-like Al/Ag bilayer film due to suppression of surface plasmon resonance for high transparent organic light emitting diodes

• We have investigated the role of an Al seed layer for an Al/Ag bilayer as a highly transparent cathode electrode.
• The measured transmittance spectra of the Al/Ag bilayer were comparable to the theoretical calculation.
• Although the thickness ranges from 4 to 8 nm, the ultrathin Al/Ag bilayer is a continuous and uniform bulk-like film.
• The maximum transmittance of transparent OLED devices was 72% at an Ag thickness of 6 nm.

We demonstrate the enhanced optical and electrical properties of an ultrathin silver (Ag) film by applying an aluminum (Al) seed layer between LiF and Ag as a transparent cathode for higher-transparency organic light-emitting diodes (OLEDs). Although the thickness ranges from 4 to 8 nm, the ultrathin Ag film is a continuous and uniform bulk-like film with an Al seed layer, which suppresses the surface plasmon absorption. Compared to an Ag-only cathode, the measured transmittance spectra were considerably increased, comparable with the theoretical calculations of a bulk Al/Ag bilayer film. The Al/Ag bilayer cathode has a transmittance of 87% at a 550 nm wavelength and a sheet resistance of 19.5 Ω/sq with a 4-nm-thick Ag layer. The transparent OLED devices that employed the Al/Ag cathode showed a transmittance of 72% at a 550 nm wavelength for an Ag thickness of 6 nm.

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