Metal-Free Transparent Three-Dimensional Flexible Electronics by Selective Molecular Bridges

Flexible and transparent electronics is a new generation of device enabling modern interactive designs, which facilitates the recent development of low-cost, lightweight, and flexible materials. Although conventional indium tin oxide material still dominates the major market, its brittleness and steadily increasing price drive scientists to search for other alternatives. To meet the high demand, numerous metallic or organic conductive materials have been developed, but their poor adhesion toward supporting substrates and the subsequent circuit patterning approach remains problematic. In this study, a robust metal-free flexible conductive film fabrication strategy is introduced. The flexible polyethylene terephthalate (PET) film is utilized as the base, where a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conductive layer is tightly linked onto this supporting substrate. An interface activation process, i.e., oxygen plasma treatment, generates PET surface active spots to react with the subsequently introduced poly(vinyl alcohol) (PVA) molecule functional groups. This spatially selective PVA molecular bridge therefore acts as a dual-function intermediate layer through covalent bonding toward PET and hydrogen bonding toward PEDOT:PSS to conjugate two distinct materials. This PEDOT:PSS/PVA/PET film delivers superior physical properties, such as a high conductivity of 38.2 Ω/sq and great optical transmittance of 84.1%, which are well tunable under conductive polymer thickness controls. The film is also durable and can maintain original electrical properties even under serious bending for hundreds of cycles. Relying on these outstanding performances, arbitrary conductive circuits are built on this flexible substrate and can function as normal electronics when integrated with multiple electronic parts, e.g., light-emitting diodes (LEDs). Superior electrical signal outputs are achieved when complicated stereo structures including folding, splicing, interlacing, and braiding are incorporated, enabling the use of these films for flexible three-dimensional electronics assembling. Space identifying smart key and lock pair, origami rabbit-carrot touch response, pressure-stimulated jumping frog, and moving dinosaur recognition designs realize these PEDOT:PSS/PVA/PET film-based human-machine interactive devices. This flexible, transparent, and conductive film generation approach by molecular bridge creation should facilitate future development of flexible or foldable devices with complex circuits.