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Because it is able to produce desalinated water directly using solar energy with minimum carbon footprint, solar steam generation and desalination is considered one of the most important technologies to address the increasingly pressing global water scarcity. Despite tremendous progress in the past few years, efficient solar steam generation and desalination can only be achieved for rather limited water quantity with the assistance of concentrators and thermal insulation, not feasible for large-scale applications. The fundamental paradox is that the conventional design of direct absorber−bulk water contact ensures efficient energy transfer and water supply but also has intrinsic thermal loss through bulk water. Here, enabled by a confined 2D water path, we report an efficient (80% under one-sun illumination) and effective (four orders salinity decrement) solar desalination device. More strikingly, because of minimized heat loss, high efficiency of solar desalination is independent of the water quantity and can be maintained without thermal insulation of the container. A foldable graphene oxide film, fabricated by a scalable process, serves as efficient solar absorbers (>94%), vapor channels, and thermal insulators. With unique structure designs fabricated by scalable processes and high and stable efficiency achieved under normal solar illumination independent of water quantity without any supporting systems, our device represents a concrete step for solar desalination to emerge as a complementary portable and personalized clean water solution.graphene oxide | solar steam | 2D water path | solar desalination | heat localization A s water scarcity (1, 2) becomes one of most pressing global challenges of our time, efficient solar desalination could provide a promising solution to produce clean water directly out of solar energy without extra energy input, particularly urgent for developing countries and remote areas without basic infrastructures (3-5). With rapid development in the past few years (6-16), it is clear that there are two key elements to enable efficient solar desalination: broadband and efficient solar absorption and localized heat management for efficient vapor generation with minimized parasitic thermal loss. So far, significant progress has been made on both of these fronts. Absorbers with various rational designs have been demonstrated with efficient solar absorption (11,14,15). Also, from dispersed particles (6, 7, 16), to porous carbon film (8, 9), to thin metallic absorbers (10,11,14,15), there is a clear trend to confine the absorbed energy in a thinner region for localized heating and more-efficient vapor generation, to minimize dissipated heat to the environment and bulk water. Impressive high-energy transfer efficiency has been achieved, but only for a limited amount of solution, with the assistance of both concentrators and thermal insulation.Efficient and effective solar desalination independent of water quantity under normal one-sun illumination without extra supporting systems will fund...

Solar steam generation is emerging as a promising technology, for its potential in harvesting solar energy for various applications such as desalination and sterilization. Recent studies have reported a variety of artificial structures that are designed and fabricated to improve energy conversion efficiencies by enhancing solar absorption, heat localization, water supply, and vapor transportation. Mushrooms, as a kind of living organism, are surprisingly found to be efficient solar steam-generation devices for the first time. Natural and carbonized mushrooms can achieve ≈62% and ≈78% conversion efficiencies under 1 sun illumination, respectively. It is found that this capability of high solar steam generation is attributed to the unique natural structure of mushroom, umbrella-shaped black pileus, porous context, and fibrous stipe with a small cross section. These features not only provide efficient light absorption, water supply, and vapor escape, but also suppress three components of heat losses at the same time. These findings not only reveal the hidden talent of mushrooms as low-cost materials for solar steam generation, but also provide inspiration for the future development of high-performance solar thermal conversion devices.