Optical properties of hollow plasmonic nanopillars for efficient solar photothermal conversion

Plasmonic nanofluids, which have superior optical properties, provide a novel way to achieve efficient solar thermal utilization. Here, the optical properties and photothermal conversion performance of hollow nanopillar structures based on four plasmonic materials (Ag, Au, Cu, TiN) were investigated and compared with the corresponding solid nanopillar structures. Numerical results show that the most significant increase in photothermal conversion efficiency is the plasmonic nanofluid based on hollow Au nanopillars, with an increase of 34.14%. The underlying physical mechanism is that the local and propagating surface plasmon resonances are further promoted in the hollow structure. In contrast, the increase of the photothermal conversion efficiency is only 1.41% for the hollow TiN nanopillars. This is due to the fact that the solid TiN nanopillars already have a high photothermal conversion efficiency of 97.19%. Thus, we can consider the enhancement of the photothermal properties of the plasmonic nanofluid by the hollow structure, especially for precious metal materials with narrow-band absorption, such as Au and Ag. For plasmonic materials with intrinsic broad-spectrum absorption (TiN, Cu), the enhancement effect is not significant. It is believed that this work will provide theoretical guidance for high-performance direct absorption solar collectors.