AZO/Ag/AZO transparent conductive films: correlation between the structural, electrical, and optical properties and development of an optical model

Multilayer transparent electrodes consisting of a tri-layer structure of Al-doped zinc oxide and silver (AZO/Ag/AZO) prepared by inline DC magnetron sputtering at room temperature were investigated. The AZO working gas pressure during deposition was identified as a crucial parameter to influence both the transmittance and sheet resistance of the transparent electrode. By a reduction of the pressure to an optimal value of 0.15 Pa, highest Figure-of-Merit values reported so far for suchlike prepared AZO/Ag/AZO systems could be achieved. In the course of layer characterization, a clear correlation between the coating microstructure and measured electrical and optical properties could be established. Furthermore, we present a model that describes the transmittance spectra of real-structure AZO/Ag/AZO tri-layer systems in a quantitative manner while explicitly considering the specific optical response of the AZO-silver interfaces. Using a generalized Maxwell-Garnett approach with a Gaussian distribution of the Depolarization factors, the interface roughness was described as an effective interfacial layer leading to an improved agreement between measured and simulated spectra.