There is an ongoing drive to replace the most common transparent conductor, indium tin oxide (ITO), with a material that gives comparable performance, but can be coated from solution at speeds orders of magnitude faster than the sputtering processes used to deposit ITO. Metal nanowires are currently the only alternative to ITO that meets these requirements. This Progress Report summarizes recent advances toward understanding the relationship between the structure of metal nanowires, the electrical and optical properties of metal nanowires, and the properties of a network of metal nanowires. Using the structure-property relationship of metal nanowire networks as a roadmap, this Progress Report describes different synthetic strategies to produce metal nanowires with the desired properties. Practical aspects of processing metal nanowires into high-performance transparent conducting films are discussed, as well as the use of nanowire films in a variety of applications.

Metal nanowire (NW) networks have the highest performance of any solution-coatable alternative to ITO, but there is as yet no published process for producing NW films with optoelectronic performance that exceeds that of ITO. Here, we demonstrate a process for the synthesis and purification of Ag NWs that, when coated from an ink to create a transparent conducting film, exhibit properties that exceed that of ITO. The diameter, and thus optoelectronic performance, of Ag NWs produced by a polyol synthesis can be controlled by adjusting the concentration of bromide. Ag NWs with diameters of 20 nm and aspect ratios up to 2000 were obtained by adding 2.2 mM NaBr to a Ag NW synthesis, but these NWs were contaminated by nanoparticles. Selective precipitation was used to purify the NWs, resulting in a transmittance improvement as large as 4%. At 130.0 Ω sq(-1), the transmittance of the purified Ag NW film was 99.1%.

This communication presents a way to produce copper nanowires with aspect ratios as high as 5700 in 30 min, and describes the growth processes responsible for their formation. These nanowires were used to make transparent conducting films with a transmittance >95% at a sheet resistance <100 Ω sq(-1).

This work describes a process to make anodes for organic solar cells from copper-nickel nanowires with solution-phase processing. Copper nanowire films were coated from solution onto glass and made conductive by dipping them in acetic acid. Acetic acid removes the passivating oxide from the surface of copper nanowires, thereby reducing the contact resistance between nanowires to nearly the same extent as hydrogen annealing. Films of copper nanowires were made as oxidation resistant as silver nanowires under dry and humid conditions by dipping them in an electroless nickel plating solution. Organic solar cells utilizing these completely solution-processed copper-nickel nanowire films exhibited efficiencies of 4.9%.

Copper metal is in theory a viable oxidative electrocatalyst based on surface oxidation to Cu(III) and/or Cu(IV) , but its use in water oxidation has been impeded by anodic corrosion. The in situ formation of an efficient interfacial oxygen-evolving Cu catalyst from Cu(II) in concentrated carbonate solutions is presented. The catalyst necessitates use of dissolved Cu(II) and accesses the higher oxidation states prior to decompostion to form an active surface film, which is limited by solution conditions. This observation and restriction led to the exploration of ways to use surface-protected Cu metal as a robust electrocatalyst for water oxidation. Formation of a compact film of CuO on Cu surface prevents anodic corrosion and results in sustained catalytic water oxidation. The Cu/CuO surface stabilization was also applied to Cu nanowire films, which are transparent and flexible electrocatalysts for water oxidation and are an attractive alternative to ITO-supported catalysts for photoelectrochemical applications.