Establishing highly stable, transparent flexible thin film heaters: Effects of ultrathin Ti wetting layer for Ag growth

Developing ultrathin Ag layer electrodes with ultralow electrical and optical losses and high thermal stability is crucial for creating efficient and thermally robust transparent heaters. However, existing techniques have struggled to produce low-loss metallic wetting layers to enhance Ag adhesion and wetting on oxide substrates. In this study, we successfully fabricated a highly efficient, ultrathin Ag layer-based transparent electrode by reducing the thickness of the Ti wetting layer to below 1 nm. The resulting electrode exhibited a high optical transmittance of 93.8 % and a low sheet resistance of 8.29 Omega sq-1. Impressively, the electrode maintained its integrity under severe mechanical and thermal loadings. To understand the underlying mechanisms, we employed high-resolution STEM and TEM to investigate the morphological evolution and crystalline features of Ag during early growth stages. Our observations highlighted the critical role of Ti in controlling Ag growth. By combining the experiment data with first-principles calculations, we determined that a 0.7-nm-thick Ti wetting layer effectively immobilizes nanoscopic clusters and suppresses cluster coalescence by increasing Ag adhesion on oxide substrates. This promotes the formation of ultrathin, continuous, smooth Ag layers. These morphological and crystallographic characteristics are essential for the outstanding performance of flexible transparent Ag thin film heaters.