Haze-free transparent electrodes using metal nanofibers with carbon shells for high-temperature stability

One of the key strategies for developing modern transparent optoelectronic devices is to achieve more conductive, transparent, and thermally-stable electrodes at minimal costs. Herein, we report a simple and cost-effective coaxial electrospinning process that produces continuous and ultra-long copper nanofibers (CuNFs) conformally covered with a shell layer of carbon black (CB). The electrospinning of Cu nanoparticles and CB inks enabled the fabrication of Cu (core)/CB (shell) nanofibers as network forms that were dispersed directly on target substrates with no additional deposition or lithography process. By virtue of the presence of the CB shell, the reflection of light from the metal surface, a critical limitation in existing metallic transparent conductive electrodes (TCEs), was reduced dramatically. Its reflection of light was even lower than that of bare quartz due to the suppressed backscattering of individual CuNFs, and this provided a high-clarity view through the black CuNF-TCEs while maintaining the high transparency of 91% and the low sheet resistance of 0.8 Ω/sq. Current-voltage experiments on single NF showed that a CuNF sustained a breakdown current density of 5 × 10⁶ A/cm², outperforming its counterpart silver NF and indicating the robustness of black CuNF-TCEs against electromigration. Such haze-free, thermally-stable black CuNF-TCEs enabled the demonstration of transparent heaters capable of working at extremely high temperatures; the maximum working temperature of the heaters was up to 800 °C, and the temperature was maintained for >90 min under an alternating current bias. We believe that the coaxial electrospinning of metal inks with other products will enable a variety of multi-functional metal NFs, leading to the development of next-generation displays, touch panels, and smart windows.