Low-temperature polyol synthesis of millimeter-scale-length silver nanowires enabled by high concentration of Fe³⁺ for flexible transparent heaters

Silver nanowires (AgNWs) emerge as a promising candidate for flexible electronic devices. AgNWs with high aspect ratios improve the optoelectronic properties of transparent conductive electrodes. However, syntheses conducted at a high temperature usually produce AgNWs either too short or too thick. Here, we report a one-pot low-temperature polyol method using a high concentration of Fe(NO₃)₃ (up to 160 mM). Fe³⁺ was found to accelerate AgNWs growth by five times, possibly reduced to Fe²⁺ and functioning as an oxygen scavenger to preserve Ag seeds, allowing the synthesis to be conducted at as low as 70 °C, which was about 100 °C lower compared with a common polyol method. Low temperature suppressed excessive nucleation, producing AgNWs longer than 1100 μm. AgNWs were dispersed in an acidic solution and purified with a non-pressure filtration method. transparent conductive electrodes fabricated with long AgNWs on polyethylene terephthalate exhibited a sheet resistance of 7.8 Ω/sq at a transmittance of 95.0% without heat treatment. Transparent heaters of AgNWs on polyethylene terephthalate and polydimethylsiloxane substrates were heated to 79.1 °C at 3 V and 174.1 °C at 8 V power supply, respectively, and their application was demonstrated in a quick defogging process. The simple synthesis method of ultralong AgNWs may expand their applications in high-performance flexible transparent electronic devices.