Construction of large-sized ultra-black films for efficient solar-thermal conversion under harsh environmental conditions

A special surface structure is required to achieve ultra-black absorption for efficient solar-thermal conversion. However, such a structure developed so far suffers from deficiencies such as small size, low tolerance to external mechanical and chemical attacks, and lack of reparability. In this study, we propose two facile methods to prepare ultra-black films with polyaniline (PANI) and polydimethylsiloxane (PDMS) by template replicating or acid etching. Experimental results show that the diffuse reflectance can be controlled to be <1.0% in the visible region (400–800 nm) for ultra-black absorption, leading to an impressive solar-thermal conversion efficiency of 88.37%. Meanwhile, the ultra-black film can be prepared by the etching method to have large sizes, large flexibility, and a diffuse reflectance of <1.0% even after 1000 loading–unloading cycles, repeated sandpaper rubbing, and long-term immersion in acids and seawater. Particularly, the film can have exceptional reparability even after severe damage. All these features are a result of the uniform constitution of the film and the reproducible bulge-valley structure on its surface. Such an excellent combination of abrasion resistance, chemical stability, and damage reparability endows the ultra-black films applicable for energy conversion under harsh environmental conditions.