Development of Self-Attachable Flexible Transparent Electrodes with Strong Mechanical and Low-Resistant Electrical Contacts

Flexible transparent conductive electrodes (FTCEs) are key elements of the emerging flexible electronic devices including flexible displays, touch panels, heaters, solar cells, electronic skins, and smart windows. In these flexible devices, the FTCEs should form a close, intimate mechanical contact and adhesion with various active components of the flexible devices to ensure stable, low-resistant electrical contacts. Unstable contact formations at the interfaces of the electrodes and active device components can cause malfunctions and performance degradation of electronics and efficiency reduction of energy devices, adversely affecting device reliability. However, FTCEs based on percolating nanomaterial networks (such as metallic nanowires, carbon nanotubes, and graphene) typically cannot adhere to other surfaces with their nanomaterials-coated side as the coated nanomaterials hinder the conformal contact of the FTCEs with the substrates. Thus, additional contact formation steps are necessary for the conventional FTCEs.<br/>Conventional contact formation methods include the use of soldering, conductive adhesives,or mechanical clamper. Alternatively, conductive metal electrodes can be formed directly on the specific active regions of flexible devices using vacuum evaporation or solution coating. While these approaches for forming mechanical and electrical junctions are well-established, they have several limitations. For example, it is challenging to form an accurate, thin contact with soldering because of the viscous fluid nature of the solder paste. Moreover, solder pastes are not transparent, which limits their utilization in specific regions of flexible transparent devices. The mechanical fixation using a sprung metal clip is typically bulky and is not suitable for thin, flexible devices. In addition, mechanical clamping can damage the surface physically. Fixations using conductive tapes and pastes (e.g., Ag paste) generally contaminate the surface and increase contact resistance owing to the adhesive chemicals at the contacting interfaces. Metal deposition can damage the active layer of devices and also requires expensive vacuum processes. Solution coating of conducting nanomaterials on a semi-finished device is also challenging owing to solvent compatibility and solvent-induced damage.Notwithstanding extensive research into flexible transparent electrodes, FTCEs that can simultaneously form low-resistant electrical contacts and strong mechanical adhesive contacts with damage-free, clean contact interfaces, and junctions have rarely been explored.<br/>Herein, we report a self-attachable, flexible, transparent, and conductive electrode (AF-TCE) that can simultaneously form strong mechanical adhesive contacts and low-resistant electrical contacts with diverse planar and curvilinear surfaces of flexible devices. The AF-TCE has a distinctive design of regular grid patterns into which bioinspired adhesive architectures and percolating Ag nanowires are integrated. Based on the integrated design, the AF-TCE can form low-resistant electrical ohmic contacts and ultra-clean, damage-free contact interfaces with active components of flexible devices by attaching it onto the components even when they are highly bent. Moreover, specific electronic circuits can be formed on the surface of the AF-TCE by depositing Ag nanowires selectively. This enables interconnections among the diverse electronic components on its surface. The advantages of the proposed AF-TCE are demonstrated by utilizing it for flexible electronics.<br/><br/>This work was supported by the National Research Foundation of Korea (NRF-2021R1A2C3006297, 2019M3C1B7025092).