Ultrasonic‐Stoichiometric Dual Regulation of Antisite Defects for Enhanced Electromagnetic Wave Absorption

ABSTRACT Antisite defect engineering has emerged as a powerful route for modulating the local electronic structure of semiconductors, offering promising opportunities to enhance electromagnetic wave (EMW) absorption. Despite this potential, the practical application of antisite defects remains constrained by their configurational instability and interference of phase transitions, leaving their influence on EMW response poorly understood. To address these challenges, a synergistic approach that couples ultrasonic modulation with precise control over chemical stoichiometry to regulate the concentration of antisite defects in CuInS 2 is introduced. Our findings reveal that ultrasonication promotes the formation of Cu In antisite defects. These defects locally disrupt lattice symmetry and, together with the ultrasonic‐induced displacement of S atoms, enable the generation of adjacent S vacancies. The resulting Cu In antisite‐S vacancy defect pairs induce pronounced polarization phenomena and enhance charge carrier transport, thereby improving conduction loss. Notably, the CuInS 2 ‐based composite prepared at a Cu/In molar ratio of 0.5 exhibits a record EMW absorption performance among CuInS 2 ‐based systems, delivering an effective absorption bandwidth of 8.24 GHz at a thickness of 2.3 mm. This study provides insights into the underlying role of antisite defects in modulating dielectric loss and suggests a promising strategy for designing high‐performance sulfide‐based EMW absorbers.