Electrically Controlled Metal‐Insulator Heterogeneous Evolution for Infrared Switch and Perfect Absorption

Abstract Active switching, which enables multifunctionality within a single optical component, is essential for reconfigurable infrared photonic systems such as radiation engineering, sensing, and communication. Metamaterials offer a solution but involve complex design and fabrication. A simpler approach with a planar layered structure becomes promising for offering economical manufacturing, easier integration, and scalability. However, it requires an active medium with giant tunability and effective modulation mechanisms. Here, an electrically controlled reversible infrared switching is demonstrated via a single layer of perovskite nickelate on an opaque substrate. Driven by the evolution of the refractive index during an electrically triggered proton‐mediated metal‐to‐insulator transition, the device transforms from a high reflective (R ≈0.74) to a low reflective state (R ≈0.09) at λ = 7–10 µm. A temperature‐independent perfect absorption (A > 0.99 at λ = 11.6–12.1 µm) emerges in the partially hydrogenated state with the mixture of the metal and insulator phases, which results in a modulation of emissivity ≈0.623 at λ = 7–14 µm. The switching behavior is tunable over a wide temperature and wavelength range, offering a versatile path for adaptive infrared applications.