Surface treatment of Cu nanowires using hydroxy acids to form oxide-free Cu junctions for high-performance transparent conductive films

Copper nanowires (Cu NWs) are promising materials for fabricating low-cost, flexible, transparent, and conductive films. However, their synthesis typically requires capping agents and their surfaces are easily oxidized, hindering NW performance. In this study, the surfaces of polyvinylpyrrolidone (PVP)-stabilized Cu NWs were treated with hydroxy acids to create impurity-free Cu junctions between the NWs. The PVP on the NW surfaces was removed in hydroxy acid solutions under neutral conditions, followed by surface oxidation. The oxides were more stable than the adsorbed PVP; therefore, this treatment completely converted PVP-stabilized surfaces into oxide-covered surfaces. The oxides were then eliminated and their surfaces were stabilized by hydroxy acids under acidic conditions. Among the tested acids, citric acid completely removed the surface oxides and best protected the NW surfaces, resulting in oxide-free Cu NWs. This treatment was then applied in combination with vacuum filtration to fabricate transparent conductive films comprised of Cu NWs. The surface treatment substantially improved the sheet resistance and transmittance of the film from 583.3 Ω/sq and 84% (at 550 nm) to 81.7 Ω/sq and 86%, respectively. The simple treatment process developed herein is expected to be widely applied to improve Cu NW performance.