Photothermal characteristics of novel flexible black silicon for solar thermal receiver

In this article, a novel type of flexible black silicon used for enhancing the absorption of a solar thermal receiver is reported. The optical absorption properties of this kind of flexible black silicon with three different sizes of conical microstructure are analyzed using the finite-difference time-domain (FDTD) method and the heat transfer properties are studied using the COMSOL multiphysics heat transfer solver. The results show that flexible black silicon with small-size microstructure has the highest optical absorptance and heat transfer speed. A commercial silicon-on-insulator wafer is irradiated by an auto-scanning femtosecond laser system and then split by etching out its middle layer in 52 % hydrofluoric acid to fabricate the flexible black silicon. The obtained flexible black silicon presents very good flexibility, and its photothermal characteristics are investigated. The optical absorption spectrum test results indicate that the absorptance of the flexible black silicon is as high as 97 % in the visible spectral region and is higher than that of anodized aluminum in a broad spectral range from 250 nm to 2500 nm. The light radiation heating experiment results show that the energy absorption efficiency of the water covered with flexible black silicon is improved 13 % compared with that of the water covered with anodized aluminum. It is confirmed that as a light-absorbing and heat-transferring layer the flexible black silicon has an important potential application in exploring solar energy.