Highly thermostable ultrathin planar Ag transparent heaters

Abstract

We report highly thermostable heaters composed of ultrathin (UT) planar Ag layers sandwiched between ZnO layers. Owing to the planar structure of the heating element, the transparent heaters exhibited excellent thermal stability and reproducibility at temperatures up to 400 °C, which is higher by a factor of three than the maximum operating temperatures of the emerging network-type transparent heaters composed of metallic nanowires. With increasing direct current voltages, the current–voltage relation exhibited three distinct zones. In Zone I, Ohmic behavior was observed with preserved structural integrity, and the heating capability was highly reproducible. In Zone II, the current plateaued with increasing voltage resulting from reduced current paths due to the solid-state thermal dewetting activated across the entire heater area. In Zone III, the current–voltage plot shows a negative slope, resulting from severe dewetting, and eventual heater failure was observed when the detwetted area coalesced to form a macroscopic electrical disconnection at sufficiently high temperatures (~700 °C). The UT–Ag heater structure, which is visibly transparent, can serve as an efficient heat-transfer blocker, confirmed by two tests using an artificial heat source and natural sunlight, rendering the transparent heaters highly suitable for energy-saving smart windows.