<p>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.</p>