Tech Boosts AgNW Electrode Conductivity, Durability

Abstract

Silver nanowires (AgNWs) are promising materials for optoelectronic devices, owing to their high transparency and conductivity. However, their performance is limited by polyvinylpyrrolidone (PVP) as an insulating capping agent that is essential for the synthesis of AgNWs but increases their intrinsic resistance. Herein, we introduce a facile spin-coating ligand exchange strategy that considers the physicochemical properties of ligands, including PVP solubility, viscosity, volatility, and hydrogen-bonding ability, to achieve a stable adsorption and efficient exchange. Among the tested ligands, ethylene glycol (EG) ligand effectively reduces the intrinsic resistance and enhances the optoelectronic properties of AgNWs by spontaneously replacing PVP and forming a stable EG⋯PVP hydrogen-bonded complex, as confirmed by multiple analysis methods. The ligand exchanged AgNWs electrode (AgNWs-EG) improves both in-plane and out-of-plane carrier transport properties as well as stability. Leveraging these properties, AgNWs-EG exhibits a 35% increase in Joule heating performance compared to the pristine AgNWs electrode and remarkable stability at elevated temperatures around 120 °C. Moreover, the performance of AgNWs-EG can be further enhanced through their combination with MXene.

Researchers at UNIST have unveiled a simple, yet effective method to replace the insulating coating-known as polyvinylpyrrolidone (PVP)-that covers silver nanowires (AgNWs), enabling significantly better electrical conductivity and enhanced durability. This innovation paves the way for the development of flexible, foldable, and rollable electronic devices using AgNW transparent electrodes.

Led by Professor Tae-Hyuk Kwon from the Department of Chemistry at UNIST, in collaboration with Dr. Ji Hoon Seo of Korea Electric Power Research Institute (KEPRI), Professor EunAe Cho of KAIST, and Professor Sang-Won Park of Suwon University, announced on the 29th that they have successfully developed a facile solution-based spin-coating process to replace the traditional insulating PVP coating on AgNWs. This approach simultaneously improves both performance and durability.

AgNWs are metallic filaments thousands of times thinner than human hair, arranged in a network that conducts electricity while allowing light to pass through, making them ideal for transparent electrodes in flexible electronic devices. However, during fabrication, PVP is used to promote nanowire growth by encapsulating their surfaces. Unfortunately, PVP also acts as an insulator, preventing efficient electrical conduction and increasing the overall resistance of the electrode.

The research team devised a method to easily exchange PVP with ethylene glycol (EG) using a simple solution process. By immersing the AgNWs in an EG solution and rapidly spinning them, the PVP coating is effectively removed, enabling a new, conductive layer to form. This layer not only enhances electrical pathways but also protects the nanowires from moisture and improves transparency.

Professor Kwon explained, "We considered various physicochemical properties such as viscosity, volatility, and hydrogen-bonding ability of potential replacement ligands. This comprehensive approach allowed us to develop an effective ligand exchange technique."

The PVP replacement resulted in a 43% reduction in electrical resistance, nearly doubling the conductivity. Moreover, the modified electrodes maintained high performance even under harsh conditions-at 85°C and 85% humidity-and showed a slight increase in light transmittance, enabling the production of brighter, more transparent electrodes.

Using these improved electrodes, the team fabricated transparent heaters that demonstrated over 35% higher heating performance compared to conventional AgNW heaters. Thanks to lower resistance, these heaters reached temperatures of 140-145°C within just six minutes of powering on, surpassing the previous maximum of 102°C.

Dr. Seo from KEPRI highlighted, "While traditional power cables are protected by external insulations to ensure electrical stability, the insulating PVP coating on AgNWs posed a challenge by increasing resistance. The new ligand exchange method provides a simple, scalable solution without complex processing or high-temperature treatments. This technology has great potential for applications in flexible displays, wearable sensors, electronic paper, and transparent heating devices in next-generation electronics."

This research was led by Junhyeok Kwon (Combined M.S. and Ph.D., Department of Chemistry, UNIST), along with Dr. HyeonOh Shin (Department of Chemistry, UNIST), and Dr. Joon-Young Soh of KEPRI. The findings were published online in Angewandte Chemie International Edition on September 30, 2025. The study was supported by the Korea Electric Power Corporation (KEPCO), the National Research Foundation of Korea (NRF), and UNIST.

Journal Reference

Junhyeok Kwon, Joon-Young Soh, Dr. HyeonOh Shin, et al., "Improving the Conductivity and Stability of Silver Nanowires Through Spontaneous Ligand Exchange for Joule Heating," Angew. Chem., Int. Ed., (2025).