Silicon nanoparticles were used as down-conversion materials on the solar cell surface to achieve better absorption in the short-wavelength range. Photoluminescent silicon Nanoparticles (NPs) have been successfully produced by electrochemical etching process. The effects of different electrochemical conditions on the properties of silicon NPs were discussed, including current density, process time, and silicon substrate resistivity. After that surface modification of Si NPs was also carried out to achieve a stable suspension, which was then spin-coated directly on the solar cell surface. Preliminary results of those Si particles showed a positive effect, an increase of 0.81% (abs.) for power conversion efficiency has been achieved in silicon heterojunction solar cells.