Influence of structural defects in nanocubes on solar photothermal conversion

The structure of nanoparticles plays a crucial role in tuning optical properties due to flexible surface modification and geometry-dependent spectrum response. Previous studies show that introducing structural defects can enhance plasmonic absorption. Here, we investigate the effects of Au nanocubes and structural defects on optical and photothermal performance. Compared with Au nanospheres, nanocubes red-shift absorption into the near-infrared and support multiple plasmonic resonances, increasing absorption by 6.63% over 300-1500 nm and achieving a solar-weighted absorption fraction of 97.11%, much higher than 80.97% for nanospheres, highlighting their potential for solar applications. Corner defects induce a blue shift of the resonance peak, weaken the second resonance, and increase scattering, reducing near-infrared absorption and solar-weighted absorption to ∼93%. Mid-side defects exhibit higher structural tolerance, enabling multiple resonances, broadening the absorption bandwidth (300-1100 nm), and suppressing scattering, with solar-weighted absorption decreasing slightly to 95.74%–96.92%. Analysis of electric and magnetic fields and thermal power shows local defects enhance fields and excite multiple resonances but do not necessarily increase peak photothermal output, revealing a trade-off between local plasmon excitation and overall performance. This work provides guidance for structural design, defect engineering, and application of Au nanocubes in direct solar thermal absorption systems.