Covalently Tethered, Semiconductor-Insulator-Conductor Polymer Networks for High-Reliability Foldable Transistors

Polymer-based foldable electronics have gained significant attention as next-generation devices in the field of display and sensor technologies because of the flexible nature of polymers. Generally, the devices possess a heterogeneously multi-layered structure, indicating that mechanical stress derived from repeated folding and unfolding conditions can propagate both bulk and interfacial regimes of each component layer. This can cause not only cohesive failure of the bulk but also interfacial delamination between the layers. Therefore, to demonstrate foldable devices with high resistance to repetitive folding-unfolding stress, it is essential to secure excellent mechanical stability at both failure points. However, most approaches only focused on either enhancing deformability of component layers or improving interface stability by utilizing physical or chemical crosslinking between layers, resulting in insufficient mechanical stability against continuous folding stress. This strongly indicates that a practical strategy to simultaneously prevent cohesive and interfacial failures is sought after for the realization of high-performance foldable electronics against severe mechanical stress.<br/>Herein, we present a novel molecular design approach of deformable and covalently attachable interpenetrating polymer networks (DcA-IPNs) in which a ladder-like polysiloxane network is physically entangled with polymer matrix (conductor, semiconductor, and insulator). The interpenetrated polysiloxane network can induce short-range aggregation of polymer and restrain fragmentation of deformed chains so that mechanical energy dissipation in the bulk regime of layers can be efficiently proceeding. Moreover, DcA-IPNs possess unreacted silanol (Si-OH) groups at their surface regimes, which is capable of the formation of covalent bonds between adjacent layers for enhanced interfacial adhesion property. Based on this, we fabricated DcA-IPNs-based foldable transistors showing high operational stability against repeated folding-unfolding stresses without degradation of their electrical performance. We believe our novel approach will provide new insights into foldable electronics.