Thermally stable indium-free transparent electrode using ultrathin Ag film

Abstract

Here we have demonstrated an indium-free transparent electrode (TE) consisting of an ultrathin silver film in combination with zinc oxide as undercoat and overcoat layer. The oxide layers help to minimize the inherent reflection of the metal film while the silver layer provides the conductivity. Electrical and optical properties of this TE have been investigated using four probe and UV–Vis spectrophotometer. Before the experimental realization of the TE, an optical simulation based on transfer matrix method has been performed to calculate the optimum thickness of the undercoat and the overcoat oxide layer to minimize the reflection loss and to get the highest transmittance. The simulation results show that thickness equal to 40 nm for both undercoat and overcoat ZnO layer gives the highest transmittance. A transmittance value above 90% (at 550 nm) with average transmittance above 85% in the visible region has been obtained theoretically and realized experimentally along with the sheet resistance below 6 Ω/□. Hackke’s figure of merit and σDC/σOP values for this ZnO/Ag/ZnO (ZAZ)-TE comes out to be better than commercially available ITO. The deposited TE and commercially available ITO were treated under different temperatures (200, 350, and 500 °C) to analyse their stability towards elevated temperature and it has been observed that ZAZ shows better stability towards temperature when compared to ITO. The high-temperature stability of this TE shows its potential for various optoelectronic applications including solar cells. Such TEs can be used in device fabrication at a higher temperature without compromising performance.