Tough and stretchable polyelectrolyte p-n junctions for flexible electronics

A scalable design integrating hydrophobic association and multivalent electrostatics yields ultra-tough, highly stretchable polyelectrolyte hydrogels for p–n junctions. • Spontaneous assembly of oppositely charged hydrogels forms transparent p-n junctions with strong adhesion (∼ 700 N/m), high toughness (2.34 MJ/m 3 ), and co-deformability (>1000%). • The resulting hydrogel diodes exhibit stable ionic rectification under extreme deformation and enable stretchable full-wave rectifiers and deformable hydrogel batteries. • This cost-effective approach advances robust, biocompatible ionic electronics for next-generation wearable, soft-robotic, and energy applications. Flexible diodes for soft electronics remain challenging in that conventional inorganic semiconductors are mechanically fragile, and many organic/2D materials lost durability under large deformation, despite the need for efficient ion transport. Hydrogel-based alternatives offer tissue-like mechanics, biocompatibility, flexibility, and functional ionic conductivity, yet conventional polyelectrolyte hydrogels typically exhibit low toughness, and limited stretchability, particularly in p-n assemblies. Herein, we present a strategy of integrating hydrophobic association with multivalent counterion–mediated electrostatics to prepare high-toughness, stretchable polyelectrolyte hydrogels in both cationic and anionic formulations. Copolymerizing a hydrophobic comonomer and ionic monomers, followed by counterion incorporation, yields transparent, volume-contracted hydrogels with matched moduli and charge densities. Oppositely charged gels are assembled by simple contact to form p-n junctions, exhibiting strong interfacial adhesion (∼700 N m −1 ), high toughness (2.34 MJ m −3 ), and ultrahigh stretchability (>1000% elongation). These junctions co-deform, recover rapidly after cycling, and maintain stable ionic rectification under strains >1000%. Beyond single diodes, the same components enable stretchable full-wave rectifiers and deformable batteries. This scalable, cost-effective approach addresses key material limitations and advances polyelectrolyte hydrogel toward applications in wearable bioelectronics, soft robotics, and energy devices. Significance statement Flexible ionic circuits are essential for soft robots and wearable bioelectronics, but their “diodes” (p-n junctions) usually fail when stretched, bent, or twisted. We report a scalable strategy for designing ultra-tough, stretchable polyelectrolyte hydrogel p-n junctions that maintain stable ionic rectification under large mechanical deformation. The key is integrating hydrophobic association with multivalent counterion-mediated electrostatics to create gels with matched mechanical properties, strong interfacial adhesion, and co-deformability. This strategy overcomes long-standing challenges faced by conventional flexible diodes of loss of contact, interfacial delamination, and rectification collapse. These innovative junctions enable robust ionic components including stretchable full-wave rectifiers and deformable batteries, offering a practical route to mechanically robust ionic electronics for next-generation wearable bioelectronics, soft robotics, and energy-harvesting devices.