The global shortage of freshwater has evolved into a fundamental bottleneck restricting sustainable socioeconomic development. Conventional desalination and wastewater remediation technologies are constrained by high energy consumption, costly infrastructure construction, and limited adaptability to scattered and remote water-deficient regions. As an emerging low-carbon water purification technology, interfacial solar steam generation (ISSG) features passive solar utilization, modular structural flexibility, and broad environmental applicability, offering a viable solution for seawater desalination, saline wastewater treatment, and complex polluted water remediation. Unlike conventional evaporation processes, ISSG involves a coupled multi-physical process encompassing solar harvesting, photothermal conversion, interfacial thermal localization, multiscale water transport, and vapor migration. Its overall efficiency fundamentally relies on the synergistic optimization of energy conversion and mass transfer. However, most existing material design strategies merely focus on single-scale structural modification or simple compositional tuning, lacking cross-scale systematic design logic, and thus struggle to achieve coordinated regulation of light absorption, heat management and water transport. In this context, the material research paradigm centered on "functional unit-ordered structure" has emerged as an innovative theoretical framework. It transcends traditional reductionism, highlighting that material macroscopic properties originate from the controllable ordered assembly of basic functional units across multiple scales, rather than the simple superposition of individual component performances.

Based on this paradigm, this review systematically establishes the conceptual connotation and theoretical system of multi-level ordered materials, and clearly distinguishes them from conventional hierarchical materials. Different from hierarchical structures that only emphasize geometric nesting at various scales, multi-level ordered materials take "order" as the core design principle, focusing on the cross-scale ordered arrangement from sub-nano meter atomic domains to nano- and microscale dimensions, as well as the functional synergy generated by inter-scale correlation. Taking hollow multishelled structures (HoMS) as the typical model system, this review comprehensively elaborates the research progress and internal regulation mechanisms of multi-level ordered materials in the field of ISSG. This paper clarifies the progressive construction logic of two ordered systems: the first level refers to nanoparticles assembled from sub-nano atomic domain functional units, while the second level corresponds to HoMS self-assembled from such nanoparticles. We systematically summarize multiple photothermal conversion mechanisms of primary functional units, including localized surface plasmon resonance of metallic motifs, bandgap modulation and nonradiative relaxation in semiconductor systems, as well as defect and amorphouse-assisted photothermal regulation. Representative material systems are analyzed in depth, revealing the inherent correlation between atomic arrangement, electronic structure and photothermal behavior.

On this basis, this review further clarifies the inherent advantages of HoMS as secondary ordered structures in optical regulation, thermal management and mass transfer. Benefiting from unique temporal-spatial ordering characteristics, HoMS enables stepwise light absorption and intershell resonant scattering, effectively broadening spectral response and extending optical propagation paths. The multilayered cavity and interfacial thermal resistance network can confine heat at the evaporation interface and suppress heat dissipation into bulk water. In terms of mass transfer, cross-scale pore channels formed by nanoparticle stacking optimize capillary water supply; nanoconfinement modulates water molecular aggregation and reduces actual evaporation enthalpy; interconnected pore pathways also provide low-resistance channels for rapid vapor escape, achieving integrated optimization of water replenishment, phase transition and vapor diffusion. Beyond HoMS, this review further extends the multi-level ordered design philosophy to a wide range of photothermal materials, including biomimetic channel arrays, gradient porous aerogels, asymmetric interface evaporators and carbon-based composite frameworks, verifying the universal applicability of this design paradigm in optimizing energy conversion and mass transport. Meanwhile, the development potential of third-level macroscopic ordered structures is further explored, and the structural superiority of micro-nano units assembled into three-dimensional architectures in ambient energy capture, latent heat recycling and directional salt migration regulation is analyzed.