Physical properties of silver nanowire networks: effects of percolation and thermal annealing

Silver nanowire networks have recently been a heavily researched subject due to their potential use as transparent electrodes in solar cells or flat panel displays. Currently, the most commonly used material for such applications (Tin-doped Indium oxide) suffers from two major drawbacks: indium scarcity and brittleness. However, metallic nanowire networks can be deposited by low cost deposition techniques and exhibit simultaneously very promising optical, electrical and electro-mechanical properties. To enhance these properties, nanowire density should be considered. For a given nanowire aspect ratio, lower nanowire densities result in higher optical transparency but demonstrate lower electrical conductivity. As the density of nanowires is increased the relationship is reversed, resulting in high electrical conductivity but low optical transparency. Numerical Montecarlo simulations on stick percolation shed light on the percolative nature of these 2D networks. Relations between simulation and experimental observations are discussed. We also show that thermal annealing can efficiently improve the electrical properties without significantly changing the optical response2. However, above a certain temperature threshold, morphological instabilities occur and induce a cancelling out of the beneficial effects. The physical mechanisms involved in thermal annealing of Ag nanowire networks are addressed as well as their effects on electro-optical properties. Finally the potential integration of Ag nanowire networks into devices is evaluated