Pushing the thinness and transparency limit of silver films for flexible optoelectronic devices via an ion-beam thinning-back process

Abstract Silver (Ag) films thinner than 10 nm are ideal candidates for transparent conductors for flexible optoelectronic devices due to their merits of a low sheet resistance (Rs), high transparency and excellent flexibility performance. Further reducing the Ag film thickness theoretically allows higher transparency but in practice leads to reduced transparency and drastically increased sheet resistance because the ultrathin film tends to be noncontinuous and unsmooth. Herein, we developed a thinning-back process to address this dilemma, in which Ag film is first deposited to a larger thickness with high continuity and then thinned back to a reduced thickness with an ultrasmooth surface, both implemented by a flood ion beam. Contributed by the slight implantation of silver atoms into the substrate during the ion-beam sputtering deposition process, high-quality Ag films with a thinned thickness down to 4.5 nm can be obtained with atomic-level surface roughness due to the implantation-induced pinning effect. Enabled by the reduced thickness, high continuity and improved smoothness, the obtained ultrathin Ag films exhibit excellent visible transparency and comparable electrical conductivity to commercial indium tin oxide (ITO). Especially, the ultrasmooth surface allows the lowest optical haze among all existing transparent conductors. As a flexible transparent conductor, the ultrathin Ag films demonstrate outstanding mechanical flexibility due to the ductility of Ag metal. Considering the overall performance of the obtained ultrathin Ag films, this ion-beam-based process presents a promising solution towards the best possible transparent conductor with ultimate thinness and transparency for flexible optoelectronic devices.