Zinc oxide and indium tin oxide as embedding layers for ultrathin-silver-based transparent electrodes: A comparative study

The triple-layered structure comprising an ultrathin (∼10 nm) Ag layer embedded between two dielectric layers exhibits high visible light transmittance, electrical conductivity, and flexibility, and this triple-layered structure is thus considered as a promising candidate to replace the conventional single-layered indium tin oxide (ITO) transparent conductive electrodes in optoelectronic devices. While various dielectrics have been employed for the underlayer and overlayer, ITO and zinc oxide (ZnO) are the two common choices. In this study, we investigated the structural, electrical, optical, and thermal properties of triple-layered electrodes (dielectric underlayer/Ag/dielectric overlayer) comprising Ag, ZnO, and ITO; namely, ZnO/Ag/ZnO, ZnO/Ag/ITO, ITO/Ag/ITO, and ITO/Ag/ZnO electrodes, in which all layers were sputter-deposited at 293 K. The deposition of crystalline Ag onto crystalline ZnO and amorphous ITO surfaces exhibited distinctly dissimilar Ag nucleation dynamics, resulting in significant differences in the structural and thus electrical characteristics prior to Ag-layer-closure. After the formation of continuous Ag layers, the electrical conductivities became similar, whereas the optimized ITO/Ag/ZnO structure exhibited a considerably higher visible light transmittance than the other electrodes (with an average transmittance of 92.8%). Further, we found that the ZnO/Ag interface stability was significantly higher than that of the ITO/Ag interface during an electrically driven Joule heating process.