In the present work, Zn2SnO4 nanoparticles were doped with silicon to improve their electrical and optical properties by the conventional solid-state reaction method. The results showed that the minimum electrical resistivity of about 0.09 cm was obtained for Zn2SnO4 nanoparticles with 3% Si doping. The decrease in the electrical resistivity can be attributed to the insertion of Si+4 atoms into the Zn+2 and/or Sn+4 sites and also the formation of more oxygen vacancies in the Zn2SnO4 lattice. The formation of the more oxygen vacancy defect states in Si-doped Zn2SnO4 nanoparticles was verified by photoluminescence spectroscopy. The efficiency of a dye-sensitized solar cell based on 3% Si-doped Zn2SnO4 was significantly better, by about 81%, compared to that of a cell based on the undoped Zn2SnO4. The enhancement in the efficiency can be ascribed to the facilitation of electron transport throughout a photoelectrode due to increase in the charge carrier concentration which was caused by Si doping.