Post-treatment optimization for silver nanowire networks in transparent droplet-based TENG sensors

Transparent conducting electrodes (TCEs) serve as essential components in various devices, including smart windows, thin film heaters, and sensors. Historically, indium tin oxide (ITO) thin films have served as the primary TCE material. However, the scarcity of indium in the Earth's crust and costly vacuum-based deposition processes have prompted researchers to seek alternatives. While silver nanowire (Ag NW) networks have emerged as the leading candidate for TCEs among various alternatives, the presence of polyvinyl pyrrolidone (PVP) layer surrounding Ag NWs often leads to substantial contact resistances at the junction areas. Given the diverse characteristics of Ag NWs, including length, diameter, PVP thickness, and deposition methods, the efficacy of a specific post-treatment method on the same Ag NW batch remained unknown. This work collected effective post-treatment methods from existing literature and innovatively developed in-house approaches to optimize the treatment of Ag NW networks. Following post-treatment, the resulting electrodes exhibited a 70 % reduction in sheet resistance, with only a marginal 1 % decrease in optical transmittance. The optical figure of merit (FoM) for the optimized networks showed a remarkable five-fold improvement, rising from 66 to 305. The optimized Ag NW networks were then utilized as current collectors in water droplet-based TENG sensors, showcasing the device's effectiveness in pH and chemical concentration sensing. The fabricated TENG recorded peak Voc and Isc values of 22 V and 370 nA, respectively. Furthermore, we developed a sensor-integrated device capable of gauging the incident droplets’ pH level, signaling acid rain safety. In addition, the droplets activate a large-area Ag NW-based transparent thin film heater. Rapid defogging and defrosting capabilities of the heater was also demonstrated. The device holds the potential to be applied to the side-view mirrors of cars, providing an anti-fogging display for a significantly safer journey.