Soft Iontronic Diodes: Materials, Mechanisms, and Progress

Soft iontronic devices, which utilize ions as charge carriers and integrate flexibility and stretchability, exhibit diverse carrier species, high biocompatibility, multimodal stimulus responsiveness, and strong resistance to electromagnetic interference. These features make them highly promising for applications in ionic circuits, flexible sensing, implantable systems, and neuromorphic information processing. Among them, soft iontronic diodes have attracted sustained attention over the past two decades as fundamental building blocks of functional circuits. This review systematically summarizes the material types of soft iontronic diodes and their influence on key device performance. It further elucidates the mechanisms underlying ionic rectification and highlights recent advances in logic gate implementation, energy harvesting, flexible sensing, and neuromorphic computing. Finally, we discuss key challenges and future opportunities in this field, aiming to provide design principles and mechanistic insights for the development and application of soft iontronic diodes.