Nanophotonics-Enabled High-Efficiency Selective Solar Absorbers for Waste Heat Management

Selective solar absorbers (SSAs) harnessing solar energy as heat and converting it into thermal energy have gained much attention, specifically in solar thermoelectric generators and solar thermophotovoltaic systems. However, most of these SSAs suffer from low solar-to-heat conversion efficiency at moderately-high temperatures (100 – 400 $^\circ$ C) and require complex nanofabrication techniques such as focused ion beam milling or electron beam lithography, hindering large-scale production. This article presents a large-area compatible and lithography-free design of SSA comprising a nanoscale multilayer stack of silica–titanium dioxide–silicon–germanium–chromium layers supported by a silicon substrate. We report 87% solar-to-thermal energy conversion efficiency with 889.4 $\mathrm{Wm}^{-2}$ net absorbing power at 100 $^\circ$ C. At this temperature, the absorption coefficient achieved is 0.90, and the emission coefficient is reported to be 0.04. A perfect match between theoretically and numerically obtained spectral responses validates our findings. The fabrication tolerance study unveils that the proposed SSA design is expected to be robust and would be less susceptible to fabrication imperfections. This angle-insensitive and polarization-independent design offers a high stagnation temperature of 378 $^\circ$ C, thus indicating that the proposed SSA can efficiently operate at high temperatures.