A one-step roll-to-roll process of stable AgNW/PEDOT:PSS solution using imidazole as a mild base for highly conductive and transparent films: optimizations and mechanisms
A recent increase in the demand for transparent electrodes has led to shortage in supply and an increase in the price of indium tin oxide (ITO) films deposited by sputter coating owing to coating speed limitations. Furthermore, flexibility has become one of the essential properties of transparent electrodes, accounting for the rapidly changing trend in electronics. These problems can be overcome by AgNW-based films suitable for flexible and stable conductive electrodes by using wet-coating-processable material and roll-to-roll coating. In this work, we developed an effective method to fabricate a highly conductive, transparent, and stable AgNW/PEDOT:PSS film using roll-to-roll slot-die coating. This coating technique provides higher line speed and greater coating uniformity. Furthermore, the optimized AgNW/PEDOT:PSS solution allows direct one-step coating without any post-treatment, such as high-temperature annealing, mechanical pressure, and solvent washing. We also studied the mechanisms of AgNW corrosion induced by the acidity of PEDOT:PSS and by hydrogen sulfide (H2S) and carbonyl sulfide (OCS) of the atmosphere. Corrosion could be prevented by neutralizing PEDOT:PSS using imidazole, which is a suitable organic compound in terms of both material and processing properties owing to its mild basicity and high melting and boiling points. In addition, the over-coating by a silica-based protecting layer on the AgNW/PEDOT:PSS film resulted in enhanced corrosion protection. The resulting roll film (460 mm in width x 20 m in length) showed suitable electrical (Rs =approx. 75 Ω sq-1) and optical (T > 90% at 550 nm, haziness =approx. 1.21%, b∗ =approx. 0.72) properties to replace ITO films in touch screen panels.