Influence of top layer thickness on the performance of WO 3 /Ag/WO 3 -transparent electrodes

This work presents a methodology based on the WO 3 /Ag/WO 3 (WAW) tri-layer configuration for obtaining indium-free TCOs by RF sputtering at room temperature. The tri-layer performance is shown to be very sensitive to the thickness variations. Through the optimization of the WO 3 top layer, it was possible to obtain a combination of thicknesses that allow to maximize the optical transmittance and at the same time lower the sheet resistance, this translates into an excellent compromise between these two properties that are usually antagonists. Using a metallic layer with a thickness that is just at its percolation limit, high electrical conductivity values can be obtained without compromising the optical transmittance. Thickness variation of the dielectric layers in turn, allowed to optimize the transport of the electrons to the metallic film. The overall tri-layer performance was evaluated using multifigure of merit analysis. Our best results were obtained for WO 3 (40 nm)/Ag(7 nm)/WO 3 (20 nm) with 1.2 Ω/sq sheet resistance and transmittance above 85%. Therefore, it is possible to obtain a TCO in an indium-free tri-layer WAW configuration at room temperature with good performance that represents a viable alternative that is not restricted by the scarcity of indium.