Effect of thermal annealing on the performance of WO3–Ag–WO3 transparent conductive film

• The optimized annealing temperature of WO3–Ag–WO3 films was found to be 100 °C.
• The sheet resistance increases with the increase of annealing temperature.
• The transmittance decreases rapidly when annealing temperature exceeded 200 °C.
• The tri-layer structure was destructed with an annealing temperature of 500 °C.
• Optical constants of WO3 layer can strongly affect the transmittance of the films.

As a candidate for transparent electrodes, oxide–metal–oxide tri-layer films have attracted a lot of interest by virtue of their low cost and decent performance. However, their thermal stability needs to be considered before device integration. Here, we report a thermal annealing effect on the performance of WO3–Ag–WO3 (WAW) transparent conductive thin film prepared by thermal evaporation. We find that the sheet resistance of the as-prepared WAW film gradually increases from 6.55 to 21.4 Ω/sq when the annealing temperature reaches 400 °C. With a low annealing temperature (below 200 °C), the luminous transmittance of the WAW film slightly increases but decreases rapidly when the annealing temperature exceeds 200 °C. The maximum figure of merit (11 × 10− 3 Ω− 1) was obtained at the annealing temperature of 100 °C. Above the annealing temperature of 300 °C, the film shows significant transmittance and conductivity degradation, which can be attributed to the decrease of intrinsic dielectric constant of WO3 layers and the reduction of connectivity between Ag islands upon high temperature annealing, respectively. Annealing at a temperature of 500 °C leads to severe destruction of the tri-layer structure. In addition, we believe that the localized surface plasmonic absorption of annealing-generated Ag nanoparticles results in a valley centered at 410 nm on the transmittance spectrum of the 500 °C annealed WAW film.