Thin-film networks of silver nanowires (Ag NWs) pose an interesting alternative to Indium Tin Oxide (ITO) as the most commonly used material in Transparent Conducting Electrodes. They exhibit electrical and optical properties to match or even surpass those of ITO, but they also demonstrate flexibility, showing little change in conductivity after cyclic loading. Here, we study the effects of two methods of producing networks of Ag NWs and compare the results with theoretical predictions for the connectivity of random fibre networks.
It is known that as the conductivity of a network of nanowires increases with increasing density, the optical transmittance decreases, therefore a compromise between these two factors is required in order to obtain an electrode that is both transparent and conducting. Nevertheless, it is possible to keep a network conductive whilst also having a high optical transmittance by using nanowires with larger aspect ratios, since fewer nanowires are required for percolation. However, SEM and TEM images suggest that longer nanowires tend to entangle, resulting in the undesirable effect of uneven distribution of the nanowires across the substrate, which leads to some regions of high conductivity and some regions of no conductivity. It is possible that this entanglement of longer wires is due to the deposition method. In order to disentangle the nanowires, and therefore provide a more uniform coverage, high shears are required. Unfortunately, these forces may lead to nanofibre fracture, thereby changing the aspect ratio of the nanowires and affecting the percolation threshold needed to achieve conductivity. For the deposition of Ag nanowires with a range of aspect ratios, we investigate inkjet printing and bar-coating methods, to form transparent conductive films. Bar coating induces shears that disentangle Ag nanowires but this leads to wire fragmentation and alignment, reducing conductivity. Inkjet printing, and by inference other droplet deposition methods, introduce less damage but are not effective at disentangling clumped fibres and thus only work effectively with lower aspect ratio nanowires.