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.
Highlights
Modern photovoltaics, light-emitting devices, touch screens and thin-film transparent heaters all rely on a transparent conductor (TC) layer for operation
We previously introduced a computational approach to describe the conduction properties of metallic nanowire networks (NWNs) using a multi-nodal representation (MNR) model which calculates the Rs considering the contributions associated with NW junctions (Rjxn) and the NW segments between them[23]
Singular values of NW length and diameter were used in all computations, the www.nature.com/scientificreports diameter was fixed at 30 nm for all simulations, the error bars arise from the standard deviation of 10 simulated networks, the simulated cell size for the above aspect ratio (AR) was 15, 30, 45 and 55 μm, respectively. (c) For the highlighted density of 0.84 NW/μm[2] with AR = 200 in (b), the average Rs was calculated as a function of the Rjxn using the MNR model, and when the inner resistance is neglected from the calculations in the junction dominated approach (JDA)
Summary
Light-emitting devices, touch screens and thin-film transparent heaters all rely on a transparent conductor (TC) layer for operation. The scarcity of indium and the high cost of the ITO film deposition has motivated the search for alternative materials, which includes conductive polymers[2], carbon nanotubes[3], graphene[4], metal mesh[5], crackle networks[6] and networks composed of metallic nanowires such as Ag, Au and Cu7–9. Each TC film requires a high optical transmittance value (T > 90%) whereas the electrical requirements of the sheet resistance (Rs) is application-specific[4]. It is clear that Ag NWNs can fulfil the required optical and electrical performances for many technologies by tuning the Rs value. Rjxn is a consequence of an electrically insulating few nm thick polyvinolpyrollidone (PVP) layer that forms a metal-insulator-metal configuration where ever NWs overlap to form a junction[23]. Modification of the PVP surface layer can give resistive switching memory effects[24,25], or enhance the thermal and chemical stability of the Ag NWNs17,26,27
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