Multicellular architectures for high-rate solar evaporation with spatial salt crystallization under high-salinity

Solar-driven evaporation offers decentralized freshwater production and brine management, yet remains limited by inefficient water transport, thermal losses and salt fouling arising from insufficient understanding of geometry-transport-performance relationships. Here, 3D-printed multicellular solar evaporators with systematically varied lattice unit cells are developed to clarify these relationships, identifying liquid-solid contact perimeter, porosity and thermal interface area as key geometric parameters governing capillary water delivery and heat transfer. Guided by these, an optimized FBCC-+_5 evaporator achieves a high evaporation rate of 6.90 kg m^-2 h^-1 and sustains zero-liquid-discharge operation. A hybrid multicellular architecture combining high- and low-evaporation-rate unit cells further generates controlled evaporation gradients, thereby localizing salt crystallization, enabling stable operation for 5.5 days with 97.49% salt recovery under 20 wt% NaCl. Outdoor desalination yields up to 47.7 kg m^-2 day^-1 of freshwater. This work establishes unit-cell and macro-scale geometry as programmable design parameters for scalable and durable solar desalination.