Epoxy-embedded silver nanowire meshes for transparent flexible electrodes

Spreading a Ag nanowire (NW) dispersion using a bar coater onto a poly(ethylene terephthalate) (PET) film and evaporating the solvent yielded a transparent NW mesh. Further spreading a solution of bisphenol A diglycidyl ether and hardeners over this mesh using the bar coater and curing the epoxy precursors produced an epoxy-embedded NW mesh or an embedded NW electrode. Various techniques including scanning electron microscopy, transmission electron microscopy, and measurements of sheet resistance and transmittance were used to monitor the electrode fabrication process, which involved NW synthesis, casting NWs onto PET or glass substrates, subjecting the NW mesh to plasma treatment, and mesh embedment by an epoxy. Using our casting method, the areal density of the spread NWs and the thickness of the epoxy layer could be readily tuned by changing the concentrations of the NW dispersion and the epoxy precursory solution concentration, respectively. Our optimized electrodes had a Ag mass density of 1.0 × 10−5 g/cm2 in the NW mesh, embedded in an epoxy layer with a thickness of 0.6 µm. While many of the NW junctions in the mesh were locked in the coating matrix, sections of the NWs were arched over the epoxy layer to provide the required electrical contact with external devices. The optimized electrodes had a sheet resistance Rs value of 18.9 ± 4.8 Ω/□ and a transmittance (T%) of 86.5 ± 0.3% at 550 nm. In addition, the embedded electrode withstood 500 cycles of bending, 500 repetitions of rubbing, and over 100 cycles of an adhesion tape test without noticeable deteriorations in their Rs and T% values. Furthermore, their high-temperature stability and sulfurization resistance were significantly enhanced over those of the unembedded electrodes and they also withstood soaking in ethanol and acetone. The ready availability and affordability of the epoxy formulation and the high control of the epoxy deposition protocol suggest that this electrode fabrication strategy has significant practical value.