One of the essential elements of flexible optoelectronics for future wearable displays, augmented reality and IoT are flexible transparent conducting electrodes (FTCEs). Silver nanowires (Ag NWs) have received a great deal of attention as future FTCEs due to their great flexibility, material stability and large-scale productivity, but these nanowires have drawbacks, such as high wire-to-wire contact resistance and poor adhesion to substrates, resulting in severe power consumption and the delamination of FTCEs.

A research team in South Korea, led by Professor Keon Jae Lee of the Materials Science and Engineering Department at KAIST and Dr. Hong-Jin Park from BSP, has developed high-performance Ag NWs (sheet resistance ~5Ω/sq, transmittance 90% at λ=550nm) with strong adhesion on plastic (interfacial energy of 30.7 J∙m-2) using flash light-material interactions.

KAIST_Ag NW_01 (cr) Figure 1: The Ag NWs on a polyethylene terephthalate (PET) film after the flash-induced plasmonic thermal process. (Source: KAIST)

The broad ultraviolet (UV) spectrum of a flash light enables the localised heating at the junctions of nanowires, which results in the fast and complete welding of Ag NWs. Consequently, the Ag NWs demonstrate six times higher conductivity than that of the pristine NWs. In addition, the near-infrared (NIR) of the flash lamp melted the interface between the Ag NWs and a polyethylene terephthalate (PET) substrate, enhancing the adhesion force of the Ag NWs to the PET by 310%.

"Light interaction with nanomaterials is an important field for future flexible electronics since it can overcome thermal limit of plastics, and we are currently expanding our research into light-inorganic interactions," Lee said.

BSP, a laser manufacturing company and a collaborator of the research, has launched new flash lamp equipment for flexible applications based on Lee’s research.

The results of this work entitled “Flash-Induced Self-Limited Plasmonic Welding of Ag NW Network for Transparent Flexible Energy Harvester (DOI: 10.1002/adma.201603473)” were published in the February 2017 issue of Advanced Materials as the cover article.