In this work, enhanced broadband solar spectrum absorption and solar-thermal conversion efficiency (~ 8%) has realized and reported by Au-decorated CuInS2 nanoparticles, namely Au@CIS NPs. The morphologies, compositions and absorptions were characterized by high resolution transmission electron microscopy (HR-TEM), UV–vis spectrometer and Finite-Difference Time-Domain (FDTD) numeric methods. The Au@CIS NPs shows a distinguished absorption perfectly matching AM1.5G solar spectrum, compared with pure Au, CIS and CIS–Au mixture nanoparticles (NPs) owing to near field plasmonic-assisted effect. In addition, the Au@CIS NPs proves its practical applications on selective distillation in non-polar solvent systems, for which the selective distillation of methylcyclohexane from toluene as an example was demonstrated. The approach can evoke future developments of plasmonic-assisted heterostructure in nanoscale for thermal solar energy harvesting application.