Purification of Copper Nanowires To Prepare Flexible Transparent Conductive Films with High Performance

Abstract

Copper nanowire (Cu NW) films have been widely studied due to their potential applications in optoelectronic devices, but there are rare reports of high-performance NW films without nanoparticles (NPs). In this paper, a waterhydrophobic organic solvent system was used to efficiently separate NPs from NWs. As a result, the transmittance of the purified Cu NW/PET films improved approximately 3% compared with the unpurified Cu NW/PET films at a given sheet resistance. And the high-quality Cu NW/PET films have a transmittance of 97.61% at 102.9 Ω sq −1 . A detailed mechanism of purification is also proposed. This facile purification method is highly efficient and widely applicable to improve the performance of flexible transparent conductive films, which will meet the need of commercial applications of NW films with excellent optoelectronic performance.

Fast Microwave-Assisted Synthesis of Copper Nanowires as Reusable High-Performance Transparent Conductive Electrode

“…This purification method can be used to specifically purify Cu NWs that were synthesized using hydrophobic alkylamine such as HDA and ODA as the capping agent. As stated above, the synthesis of Cu NWs in this work uses ODA as capping agent which is an amphiphilic molecule that has a hydrophilic amino head and a long hydrophobic alkyl tail that contributes to its hydrophobicity [51,52]. Products of the synthesis of Cu NWs usually consist of NWs and undesired NPs, and the amount of NPs usually increased in larger reaction volume.…”

“…Figure 4 shows the mechanism of the separation of Cu NWs and Cu NPs based on their surface properties as proposed by Kang et. al [51]. After addition of water and chloroform (CHCl3), both of the solutions are phase-separated due to their immiscibility, in which CHCl3 stayed below due to its higher density.…”

“…When the solution was shaken, only a small amount of organics on the surface of Cu NWs dissolved into CHCl3 (Figure 4b). This is due to the formation of NWs meshes that prevent the residual organics from directly contacting with CHCl3, and the twin defects existence in NWs which contributed to the stronger adsorption of twin boundaries to the capping agents [51,54]. On the other hand, the residual organics on the surface of Cu NPs were completely removed by CHCl3 when the solution was shaken due to their monodispersity with organic solvents and weak adsorption to organic materials.…”

“…The decrease in transmittance value was due to the presence of NPs in NWs which act as the center of light scattering. In addition, they do not contribute to the overall electrical conductivity due to their isotropic shape with poor connection on the percolating nanowire network [51,62,63]. Furthermore, it is very important to study the chemical stability of Cu NWs film.…”

“…4c shows that the force between residual organics and CHCl3 that drives the NWs into CHCl3 when the CHCl3 reassembled below water. An aqueous film was formed on Cu NPs' surface due to the bonding of oxygen atoms of the water molecules with the bare Cu atoms[51]. As a result, the NPs that were surrounded by water were repelled by CHCl3 and dispersed well in water.…”