In-Situ Redox Nanowelding of Copper Nanowires with Surficial Oxide Layer as Solder for Flexible Transparent Electromagnetic Interference Shielding

Abstract

Silver nanowire (AgNW) transparent electrode stands out as a promising candidate to replace indium tin oxide (ITO), whereas the high cost and electromigration of silver ions overshadow the applications of AgNWs in optoelectronics. Copper nanowire (CuNW) is attracting increasing interest and attentions due to its high intrinsic electrical conductivity, earth abundance and lower prince, but the oxidation of CuNW severely prohibits its practical applications, which is an issue to be solved urgently. Herein, nanowelding of CuNWs is achieved via an in-situ redox approach. In this welding process, the copper oxide on the surface of CuNWs as a natural solder is reduced by sodium borohydride (NaBH4) to generate Cu atoms, which selectively aggregate at the intersection of CuNWs and merge the junction owing to the positive site here. The sheet resistance of welded CuNW (W-CuNW) transparent conducting films drop obviously without sacrificing its transmittance, which thereby significantly promotes the optoelectronic performance of the film. Poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) as a protective layer is coated onto the W-CuNW film to prepare PEDOT:PSS/W-CuNW film. The optoelectronic properties of the PEDOT:PSS/W-CuNW film show excellent stability in ambient atmosphere for 30 days. Beside, no obvious change in the sheet resistance of the PEDOT:PSS/W-CuNW film is observed after 5000 bending cycles under a bending radius of 2 mm, indicating the outstanding mechanical flexibility. Finally, electromagnetic interference (EMI) shielding effectiveness (SE) of the PEDOT:PSS/W-CuNW film is measured within the frequency range from 8.2 GHz to 12.5 GHz. The PEDOT:PSS/W-CuNW film with a EMI SE value above 27 dB and transmittance of 85% underlines the great potential applications in displays, touch panels, airborne optoelectronic pods and aviation camcorders.