Solar Selective Absorbers for High-efficiency Photothermal Conversion via Core–Shell Nanocone Structured Surface

Nanostructured surface, a promising photon management strategy, enables to enhance photon-to-heat conversion efficiency by manipulating spectral radiative properties ranging from solar spectrum (0.3–2.5 μm) to mid-infrared spectrum (2.5–20 μm). Here, a core–shell nanocone structured surface made of silica core and tungsten shell as a solar selective absorber is introduced. The photothermal conversion efficiency (PTCE) is calculated in consideration of solar spectrum absorption and mid-infrared emission. It is obvious that high solar spectrum absorption and low mid-infrared emission are beneficial for high PTCE. The influence of structural parameters on the PTCE is studied, and then the absorption enhancement mechanism is elucidated in detail. Meanwhile, the influences of incident angle, polarized state, and lattice arrangement are also presented. The calculated results exhibit that our optimized solar absorber possesses the total solar absorption of 97.3% and total thermal emission of 7.6%, resulting in a maximum PTCE of 91.4% under one sun illumination conditions at normal incidence. Moreover, our solar selective absorber is independent to the incident angle and polarization state. The excellent photothermal conversion performance with wide-angle and polarization-insensitive properties for the solar selective absorber can serve as a good candidate for various solar thermal applications including seawater desalination, steam generation, thermophotovoltaic, and photocatalysis.