Synthesis and highly effective purification of silver nanowires to enhance transmittance at low sheet resistance with simple polyol and scalable selective precipitation method

Abstract

Networks of metal nanowires (NWs) have the highest performance of any solution-coatable material to replace expensive indium tin oxide (ITO) as the transparent conducting electrode material in next-generation devices. However, there is as yet no published process for producing NW films with an optoelectronic performance that exceeds that of ITO. Here, we examine a process for the synthesis and purification of uniform AgNWs that, when coated using a spin-coating technique to create a transparent conducting film, show properties that exceed those of ITO. The morphology AgNWs can be controlled by adjusting the concentration of silver nitrate (AgNO₃) and [PVP] to [AgNO₃] molar ratio. AgNWs with average diameters of 20 nm and aspect ratios >1000 were obtained by adding 30.5 mM of AgNO₃ and 6 : 1 molar ratio of [PVP] to [AgNO₃] in a silver nanowire synthesis, but these NWs were contaminated by some Ag nanoparticles. Selective precipitation was used to purify the NWs from nanoparticles, resulting in a transmittance improvement as large as 2%. The transmittance of the purified AgNW film was 97.5% at a sheet resistance of below 70 Ω sq⁻¹. The synthesized and purified AgNWs were analyzed by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible-near-infrared (UV-Vis-NIR) spectroscopy and four-point-probe technique.