Thin film technology for solar steam generation: A new dawn

The sun is considered as the most promising abundant renewable energy source that can be exploited to solve many of human beings' challenges such as energy and water scarcity. Solar energy can be utilized in steam and vapor generation processes which has a great importance in many engineering applications such as water desalination, domestic water heating, and power generation. However, dilute solar flux (similar to 1000 W/m(2)) cannot supply the absorber with enough power required to overcome water latent heat of vaporization to evaporate water. Optical concentrators such as parabolic trough collector, parabolic dish reflector, and circular Fresnel lens can be used to concentrate the solar radiation to achieve the required power however they suffer from complexity and high cost. Moreover, the efficiency of the conventional solar desalination devices such as solar stills decreases dramatically with increasing bulk water quantity, due to the heat loss to bulk water. Therefore, the need to solar steam generation (SG) devices, that localize heating on a thin layer of water rather than the water bulk, arises. Thin film technology has shown promising progress in SG in which solar energy is utilized to wastewater desalination. The past five years have seen a significant surge in the development of thin film based SG devices. In this review, recently developed thin film-based SG devices are scrutinized with respect to their physical mechanisms, fabrication methods, structure, advantages, and disadvantages. Different types of thin-film materials, including: metal-based nanoparticles, metal oxides, carbon-based materials, polymers, etc.; as well as different substrates materials, including: wood, paper, cotton fabric, carbon fabric, polystyrene foam, and gauze, have been discussed. Moreover, different preparation and synthetization methods of the steam generation devices have been discussed. Suggestions for future research directions are also presented.