Field‐Driven Assembly of Orientation‐Controlled Anisotropic Colloidal Frameworks for Broadband Perfect Optical Absorption

ABSTRACT

Developing optical‐material architectures capable of broadband and efficient light absorption across diverse material systems, particularly nonmetallic and low‐loss materials, remains a major challenge for light‐harvesting and optoelectronic applications. Here, we present an orientation‐controlled, spatially aperiodic, non‐close‐packed anisotropic colloidal framework that achieves near‐perfect broadband absorption. Magnetic‐ or electric‐field‐assisted assembly combined with solution coating or atomic layer deposition is employed to realize the designed architectures, supporting flexible configurations including rod‐ and ellipsoid‐based building blocks, internally embedded or externally coated absorbing components, and diverse functional materials such as metals, oxides, and semiconductors. Compared with conventional isotropic sphere‐based microstructures, anisotropic colloidal architectures exhibit superior light‐harvesting performance. Remarkably, even oxide materials such as Fe ₃ O ₄ enable near‐perfect broadband absorption, with average absorptivities reaching 99.8% in simulations (300–1500 nm) and 97.4% experimentally (400–1100 nm). Partially aligned non‐close‐packed anisotropic geometries regulate optical transport by suppressing backward reflection, redistributing scattering pathways, and enhancing internal light confinement, thereby enabling broadband angular‐ and polarization‐insensitive absorption. An interpretable machine‐learning framework reveals quantitative structure–property relationships governing broadband optical absorption, providing quantitative guidance for optimizing 3D anisotropic structures under different thickness constraints. This work provides a versatile strategy for engineering broadband light‐management architectures, offering broad material compatibility, structural tunability, and potential for scalable fabrication.