RuO₂ Supercapacitor Enables Flexible, Safe, and Efficient Optoelectronic Neural Interface

Abstract Optoelectronic biointerfaces offer a wireless and nongenetic neurostimulation pathway with high spatiotemporal resolution. Fabrication of low‐cost and flexible optoelectronic biointerfaces that have high photogenerated charge injection densities and clinically usable cell stimulation mechanism is critical for rendering this technology useful for ubiquitous biomedical applications. Here, supercapacitor technology is combined with flexible organic optoelectronics by integrating RuO₂ into a donor–acceptor photovoltaic device architecture that facilitates efficient and safe photostimulation of neurons. Remarkably, high interfacial capacitance of RuO₂ resulting from reversible redox reactions leads to more than an order‐of‐magnitude increase in the safe stimulation mechanism of capacitive charge transfer. The RuO₂‐enhanced photoelectrical response activates voltage‐gated sodium channels of hippocampal neurons and elicits repetitive, low‐light intensity, and high‐success rate firing of action potentials. Double‐layer capacitance together with RuO₂‐induced reversible faradaic reactions provide a safe stimulation pathway, which is verified via intracellular oxidative stress measurements. All‐solution‐processed RuO₂‐based biointerfaces are flexible, biocompatible, and robust under harsh aging conditions, showing great promise for building safe and highly light‐sensitive next‐generation neural interfaces.