Bridge Solubility in Liquid Metals Enables the Synthesis of Ultrathin Fluorine-Doped Tin Oxide

Abstract

Fluorine-doped tin oxide (FTO) exhibits the nexus of transparency, electrical conductivity, heat resistivity, and reduced reliance on critical minerals, making it vital in solar panels, IR-reflective glass, and optical electronics. This work leverages the synergistic combination of two emerging liquid metal-based concepts—liquid metal doping and liquid metal bridge solubility—for the generation of ultrathin FTO layers, reducing reliance on current energy-intensive and hazardous chemical vapour deposition (CVD) processes. Here, tin (Sn) and silver fluoride (AgF) are melted together to form a homogeneous liquid, from which the surface oxide is transferred onto a solid substrate. While Ag plays an essential role in facilitating the incorporation and solubility of F in Sn, its presence at the liquid metal surface is restricted due to its very low tendency to oxidise at the surface. The technology enables the harvesting of multilayer architectures at moderately low temperatures and under ambient atmospheric conditions. The harvested FTO nanosheets exhibited a thickness of up to 10 nm, enhanced conductivity, and a transparency of 80% in the visible region. Tin oxide (SnO₂), obtained from a similar liquid metal-based deposition process, was also used as a reference for comparison. This work validates the feasibility of liquid metal-based technology for the efficient synthesis of ultrathin doped oxides as a potential alternative to complex and energy-intensive state-of-the-art sputtering and CVD techniques.