Cascaded Built‐In Electric Fields Engineering for Electromagnetic Wave Absorption

ABSTRACT Built‐in electric fields (BIEF) at heterointerfaces create non‐equilibrium energy gradients that amplify dielectric response without sacrificing impedance matching, improving electromagnetic wave absorption (EWA). However, in cascaded BIEF systems formed by morphology control and multiphase hybridization, the impacts of dipole orientation and band‐edge connectivity on dielectric attenuation remain unclear. Herein, we synthesize two core–shell hybrids (metal@oxide@carbon and metal@multiphase hybridized carbon), with phase complexity evolving from four to six, via ultrasound‐assisted galvanic replacement of liquid metal, metal‐organic framework coating, and in situ pyrolysis. By programming radial work function profiles into mountain‐shaped or monotonic staircase, the counter‐ and co‐directional cascaded BIEF were realized. The former suffers interface dipole vector cancellation, while the latter exhibits superposition, strengthening local fields and cross‐layer coupling to promote charge separation and interfacial relaxation. Additionally, the carbon shell narrows the bandgap and enriches π electrons, increasing carrier excitation and mobility to deliver a controlled rise in conductive loss. The co‐directional cascaded BIEF sample achieves impressive reflection loss (−58.81 dB) and bandwidth (6.39 GHz), and its EWA patch suppresses electric‐field radiation to below 10%. Overall, this work establishes a cascaded BIEF engineering paradigm, expanding the conceptual boundaries and application scope of BIEF‐driven EWA materials.