The Electro-Optical Performance of Silver Nanowire Networks

Abstract

Networks of metallic nanowires have the potential to meet the needs of next-generation device technologies that require flexible transparent conductors. At present, there does not exist a first principles model capable of predicting the electro-optical performance of a nanowire network. Here we combine an electrical model derived from fundamental material properties and electrical equations with an optical model based on Mie theory scattering of light by small particles. This approach enables the generation of analogues for any nanowire network and then accurately predicts, without the use of fitting factors, the optical transmittance and sheet resistance of the transparent electrode. Predictions are validated using experimental data from the literature of networks comprised of a wide range of aspect ratios (nanowire length/diameter). The separation of the contributions of the material resistance and the junction resistance allows the effectiveness of post-deposition processing methods to be evaluated and provides a benchmark for the minimum attainable sheet resistance. The predictive power of this model enables a material-by-design approach, whereby suitable systems can be prescribed for targeted technology applications.

The resistance of Cu nanowire–nanowire junctions and electro-optical modeling of Cu nanowire networks

“…The shape of the experimentally acquired T-Rs curve is also important, as networks which are not fully optimized through post-processing can exhibit abnormal T-Rs profiles that deviate from the standard shape, and which the MNR and MLST model can highlight. 11 In all cases reported here, the MNR and MLST model utilizing a ⟨Rjxn⟩ = 205 Ω accurately predicts the performance of real world networks. This indicates that the high-current electroforming process employed in the measurement of the single NW junctions in this work reproduces a Rjxn comparable to the postprocessing methods employed in the fabrication of Cu NWNs.…”

“…The model and the code is described in detail and is available in an earlier publication. 11 For predicting the performance of Cu NWNs, the material resistivity was set at ρ = 20.1 nΩm, while Rjxn was varied according to experiment. The extinction cross section, Cext, was calculated using the MatScat (Mie theory for infinite cylinders) implementation by Schäfer et al 16 using various values for NW diameter and the optical constants for Cu, n = 1.0344, k = 2.57984 at λ = 546 nm.…”

“…9 We recently published a method which accurately describes the electrical and optical performance of Ag NWNs using a multi-nodal representation (MNR) of a NWN, that is, considering both the resistance contribution of the NW junctions and the NW segments between them; coupled with an optical model based on Mie light scattering theory (MLST). 11 The electrical results presented above allow the MNR and MLST model to be applied to Cu NWs, predicting the electro-optical performance of a Cu NWN transparent conductor electrode using only physical properties such as NW length (L) and diameter (D), electrical parameters such as ⟨ρ⟩ and ⟨Rjxn⟩, and the optical constants of Cu. By choosing physical parameters that match datasets already published in the literature, we can test the MNR and MLST model on its predictive accuracy.…”

“…The resistance of Ag NW junctions has been previously established, 9,10 and has enabled the comparison of post-processing conditions which remove the insulating polymer coating from the polyol synthesis method, and assisted in the development of accurate computational models predicting the performance of Ag NWN-based materials. 11,12 One drawback to Cu NWs is that they readily oxidize in ambient conditions, insulating the conducting core and causing a large contact resistance at each of the nanowire-nanowire junctions. Post-processing methods have been developed to remove the oxide layer, which include, acetic acid washes, plasma cleaning, hightemperature hydrogen annealing, and photonic welding.…”

Effect of tunneling on the electrical conductivity of nanowire-based films: Computer simulation within a core–shell model

“…Nanowire networks (NWNs) have excellent optical, electrical and mechanical performances, which makes them very attractive for use as transparent electrodes in modern photovoltaics, light-emitting devices, touch screens, and thin-film transparent heaters. 1 These applications require high transmittance of transparent electrodes while their sheet resistance should be within different ranges. 1,2 The required sheet resistance varies from 500 Ω/ in the case of touch screens to 1 Ω/ in the case of solar cells.…”