Seawater desalination and wastewater purification technologies are the main strategies against the global fresh water shortage. Among these technologies, solar-driven evaporation is effective in extracting fresh water by efficiently exploiting solar energy. However, building a sustainable and low-cost solar steam generator with high conversion efficiency is still a challenge. Here, pure organic aerogels comprising a cellulose scaffold decorated with an organic conducting polymer absorbing in the infrared are employed to establish a high performance solar steam generator. The low density of the aerogel ensures minimal material requirements, while simultaneously satisfying efficient water transport. To localize the absorbed solar energy and make the system floatable, a porous floating and thermal-insulating foam is placed between the water and the aerogel. Thanks to the high absorbance of the aerogel and the thermal-localization performance of the foam, the system exhibits a high water evaporation rate of 1.61 kg m−2 h−1 at 1 kW m−2 under 1 sun irradiation, which is higher than most reported solar steam generation devices.