Effects of the structural properties of metal oxide/Ag/metal oxide multilayer transparent electrodes on their optoelectronic performances

In this study, we prepared metal oxide-metal-metal oxide (OMO) multilayer transparent electrodes based on indium tin oxide (ITO) and ZnO, viz., ITO/Ag/ITO (IAI) and ZnO/Ag/ZnO (ZAZ) by sputtering and investigated the influence of the thickness of the silver layer as well as the thickness and surface roughness of the metal oxide layers on the optoelectronic performance of the electrodes. The surface roughness of the metal oxide layers affect the critical thickness required to transform the low-conductivity semi-continuous silver films into high-conductivity continuous ones. The thicknesses of the metal oxide layers over and underneath the Ag layer can be modulated not only to enhance the transmittance of the electrodes but also to adjust the position of the maximum transmittance. Optimization of the thicknesses of the metal oxide and Ag layers allows the fabrication of high-quality transparent electrodes. The sheet resistance for the best ZAZ sample was 4.16 Ω/sq while the average transmittance (including glass) was 73.09% in the visible region. For IAI electrodes, the sheet resistance and the average transmittance in the visible region were 5.85 Ω/sq and 82.12%, respectively. The Haacke index indicated that for applications with high optical demands, the Ag film thickness should be 8.5 nm and 13.0 nm for ITO and ZnO systems, respectively. Moreover, semi-continuous Ag layers are bluish due to surface plasmon resonance. This study defines a criterion for determining the optimal thickness of Ag layers in OMO films.