Weathering and Material Characterization of ZTO/Ag/ZTO Coatings on Polyethylene Terephthalate Substrates for the Application of Flexible Transparent Conductors

Abstract

Flexible transparent conducting coatings have been adopted in many novel optoelectrical devices for energy-related applications. Laminated coatings composed of oxide/metal/oxide (abbreviated as OMO) layers are promising alternative materials to indium tin oxide (ITO). However, the durability and weatherability of free-standing OMO samples—including laminated OMO coatings and polymeric substrates—affects the performance of the related optoelectrical components and devices. It is necessary to study the degradation mechanisms in terms of optoelectrical and mechanical properties through the weathering tests. In this study, we performed indoor accelerated and outdoor weathering tests on commercial OMO samples composed of ZTO/Ag/ZTO coatings on polyethylene terephthalate (PET) substrates. The effects of environmental stressors such as ultraviolet (UV) radiation, elevated temperature, and mechanical bending on the degradation behaviors of OMO samples were investigated. Comprehensive material characterizations including UV–Vis spectroscopy, four-point probing, tensile tests, and Raman spectroscopy were carried out. The OMO coating was robust against the weathering tests, while the PET substrates underwent embrittlement upon long-term weathering. The embrittled PET substrates consequently impaired the mechanical flexibility and bendability of the OMO coatings. The results of this study provide an in-depth understanding of the durability and weatherability of silver-based OMO flexible transparent conductive materials.