Synergistic Solar‐Powered Water−Electricity Cogeneration from Diverse Saline Water Enabled by a Multistage Solar Still Based on Zwitterion‐Modified Janus Membranes

ABSTRACT The global pursuit of sustainable development is increasingly constrained by freshwater scarcity and the growing energy crisis. Integrating solar‐powered hybrid systems that couple photovoltaic electricity generation with passive steam‐based desalination offers a promising solution. Although thermally localized multi‐stage solar stills have been explored, stable water production in saline environments remains challenging. Herein, a photovoltaic (PV) cell integrated with a nine‐stage membrane distillation (MD) device are developed, enabling simultaneous electricity and clean water generation from diverse saline water (3.5%–20%). Zwitterion‐modified Janus membranes, together with the multi‐stage architecture, synergistically cool down the PV cell, suppress salt crystallization, recycle vaporization enthalpy, and repurpose waste heat. As a result, the integrated device achieves a high water production rate of 3.89 kg m −2 h −1 , while simultaneously maintaining a stable electricity generation efficiency of 15.3% under 1 sun, maximizing the total solar energy conversion. Under natural sunlight, a daily clean water yield of 10.8 kg m −2 day −1 is achieved, placing this system among the best‐performing solar stills reported to date. This study highlights a low‐carbon cogeneration of clean water and electricity, extending the applicability of solar conversion technologies to saline environments.