Copper grid embedded polyimide exhibiting high electrical and optical performance as transparent electrode using electrohydrodynamic printing

Abstract

Transparent electrode, as an important component in various kinds of electronic devices including touch panel, solar cell, and display, has attracted much attention. Commercially used indium tin oxide (ITO) exhibits excellent electrical and optical properties but suffers from brittleness due to its oxide nature. With rising demands for flexible electronics, flexible transparent electrode has been researched to replace ITO, for example conducting polymer, graphene, metal nanowires and metal grids. Among them, metal grid shows good optical and electrical properties because of its highly organized structure and metal is highly conductive. Electrohydrodynamic (EHD) printing is an efficient and high precision technique that is suitable in metal grid patterning. In this study, copper grid embedded polyimide thin film was fabricated using EHD printing, wet etching, and embedding techniques, and electrical and optical properties were examined. Copper grid shows optimal performance of $15 \Omega /sq$ sheet resistance and 95% transmittance with $5 \mu m$ wire diameter and $200 \mu m$ pitch. Aging test demonstrates the thermal and long-term stability of sample and bending test proves the desired flexibility and bending stability of embedded thin film. The fabricated embedded polyimide was tested for the application of heater and it shows stable heating capability.