Characterization of Ag/ZnS/Ag multilayered film as transparent electrode for organic light-emitting diode

Ag/ZnS/Ag (AZA) multilayer films with various ZnS interlayer thicknesses were deposited on glass substates by thermal vacuum evaporation. The transmittance, reflectance, and sheet resistance of the films were investigated for their use as the transparent electrode of an organic light-emitting diode (OLED). A transmittance peak and reflectance valley showed red-shift by changing the interlayer thickness and thus corresponded well. The sheet resistance of the AZA multilayer films was lower than that of indium tin oxide, which is suitable for usage as a transparent electrode for OLED. Next, the OLED devices with AZA multilayer films of different interlayer thicknesses were fabricated, and the device performance and electroluminescence (EL) spectra were evaluated. Unexpectedly, the emission color of AZA-OLED changed from yellow to sky blue when the thickness of ZnS interlayer went from 30 nm to 60 nm. According to the correspondence between EL and reflectance spectra, the observed color change can be attributed to the dominance of a microcavity effect rather than plasmon-induced color filtering. The calculated external quantum efficiency was the highest when the ZnS interlayer thickness was 30 nm compared to the other AZA-OLEDs and conventional OLEDs.