<p>Solar energy has attracted widespread scholarly attention due to its capacity to cut carbon emissions and advance the energy transition. Direct absorption solar collector (DASC), which is a critical part of the photothermal conversion utilization, would be improved by utilizing nanoparticles (NPs). Most existing studies on core–shell structures for DASC focus on single-core–shell configurations, while investigations of multicore–shell structures for DASC remain limited. In this work, a multicore–shell structure is proposed to systematically compare the photothermal conversion efficiency of single-core versus multiple-core Au@SiO₂ nanoparticles. Considering the localized surface plasmon resonance (LSPR) of metallic particles of Au and the thermal stability of silicon, single-Au@SiO₂ and multiple-Au@SiO₂ are analyzed via COMSOL Multiphysics based on the finite element method (FEM). The findings exhibit that the photothermal conversion efficiency (<i>η</i>_abs) of multiple-Au@SiO₂ approaches 90% at lower volume fractions and optical paths in comparison with single-Au@SiO₂. Photothermal conversion efficiency is reduced with a growing SiO₂ shell radius. In addition, the effects of the Au core radius and interparticle gap on the absorption properties are analyzed. Therefore, this study reveals that the application of multicore–shell nanoparticles is beneficial for future research on promoting solar absorption properties.</p>