Influence of thermal annealing on the optical and electrical properties of Ag-Al ultrathin film-based sandwich-like transparent conductor

Heating process is always needed and sometimes inevitable in fabricating high-performance transparent conductors. In this work, the thermal stabilities of the optoelectronic properties of the annealed Ag-Al ultrathin film and the sandwich-like structure of TiO2/Ag-Al/aluminum-doped zinc oxide (AZO) are systematically investigated under different annealing temperatures and durations. After annealing at 200 °C for 20 min, the pure Ag layer dewets into isolated islands completely, but the Ag-Al alloy ultrathin film retains continuous film morphology with low sheet resistance, demonstrating alloying with Al element can effectively improve the thermal stability of the Ag layer. However, increasing the annealing duration further upon Ag-Agl alloy film will lead to serious dewetting, agglomeration, and increased resistance. The TiO2/Ag-Al/AZO sample has a high optical transmittance, which can be maintained after annealing at 200 °C for 60 min. Nevertheless, when annealing at 300 °C its sandwiched structure is destroyed as a result of the agglomeration of the Ag-Al layer. The annealed TiO2/Ag-Al/AZO structure has an average transmittance of about 85.4% in the range of 400–700 nm and a sheet resistance of 12.5 Ω.sq−1, indicating the potential for the high-performance transparent conductor application.