Enhanced electrical outputs of thin-film solar thermoelectric generator with optimized metal/dielectric multilayered solar selective absorber

In solar thermoelectric generators (STEGs), solar selective absorbers play a vital role in enhancing the light-to-heat conversion efficiency by improving sunlight absorption and reducing heat radiative loss. Nevertheless, the light-to-heat conversion efficiency depends strongly on the operating condition, which needs to be optimized to suit the practical application. In this work, Cr/SiO${}_2$-based six-layer solar selective absorber was designed to maximize the photothermal conversion efficiency for the operating temperature of 300 or 600 K and solar concentration ratio of 1 Sun. Series-connected p-type Bi${}_{0.5}$Sb${}_{1.5}$Te${}_3$ and n-type Bi${}_2$Te${}_{2.7}$Se${}_{0.3}$-based planar thin-film STEGs were prepared by shadow-mask-assisted magnetron sputtering with the designed solar selective absorber or black paint as the solar heater. When exposed to a standard solar simulator without any optical concentration, the thin-film STEG with the solar selective absorber optimized for 300 K exhibits the highest electrical outputs (1.3 mV and 0.3 µA), while the STEG with solar absorber designed for 600 K shows a lower outputs, even less than the one with black paint. The results demonstrate that not only the solar absorptance and thermal emittance, but also operating conditions should be particularly considered in designing solar selective absorbers.