Effect of argon plasma treatment on transparent electrodes based on silver nanowire networks

Transparent conducting materials (TCM) play a pivotal role in many modern devices. However, the most used TCM (ITO, Indium Tin Oxide) suffers from two major drawbacks: brittleness and indium scarcity. Among emerging TCMs used as transparent electrodes, silver nanowire (AgNW) networks appear as a promising alternative to ITO, with typical sheet resistance of 10 Ohm/sq and optical transparency of 90%, combined with good mechanical flexibility. The fabrication of these electrodes often involves low-temperature processing steps and scalable methods, thus making them ideal for low-cost transparent electrodes in flexible electronic devices. The reduced sheet resistance of AgNW networks, however is usually obtained by thermal annealing of the material up to 300 °C in air. Although this treatment drastically reduces junction resistances, this high temperature is not ideal for temperature-sensitive process steps in manufacturing. Moreover, reduced thermal budgets are desired in some applications. In this work, we present an alternative approach by sintering the as-deposited AgNW networks with plasma exposure. The high energy ions from an Ar plasma interacts with the AgNW and locally sinter the AgNW together, forming a conducting path across large distances over the network. The aim of such an approach is to reach similar electrical and optical performance characteristics as in thermally-treated materials but with a significantly lower thermal budget. Plasma exposure also offers a better surface homogeneity compared to thermal annealing, which is affected by the mismatch of thermal conduction between the glass substrate and the metallic nanowires, and reduces the impact on the integrity of flexible polymer substrates. In this work, we report on a study of the effect of the plasma power and the exposure time on the morphological, electrical and optical properties of AgNW networks and we demonstrate that a fine tuning of these parameters is needed to obtain transparent electrodes with competitive characteristics.