Photo-Thermoelectric Conversion Using Black Silicon with Enhanced Light Trapping Performance far beyond the Band Edge Absorption.

During the past years, much research work has been focused on efficiently harvesting solar energy with black silicon (b-Si). However, semiconductor Si can only utilize solar energy with wavelength smaller than λ = 1110 nm (bandgap Eg = 1.12 eV) for photovoltaic applications or photoelectrochemical conversions. Light with wavelength beyond the band edge (above λ = 1110 nm) cannot be used. Here, we prepared highly conductive b-Si without an apparent optical bandgap by a reactive ion etching process, which can largely absorb light with a wide range wavelength and even far into the near-infrared region (∼2500 nm). The optimized b-Si with surface texture shows the specular reflection rate lower than 0.1% and the average total reflection (specular reflectance + diffuse reflectance) is about 1.1%. Additionally, we briefly introduce the mechanism and reflection principle of surface nanostructured b-Si. By using b-Si structured material, we successfully convert the solar energy to electric power via photo-thermoelectric conversion, especially solar energy exceeding 1110 nm wavelength can also be efficiently used. The excellent light trapping of sunlight shows great potential for photothermal applications, such as photothermal imaging, seawater desalination, and further applications.