In order to achieve low cost and high efficiency solar cells, all silicon tandem solar cells made of Si nanocrystal (Si NC) thin films with different bandgaps (such as Si/SiO2 Si NC thin films) stacking on crystalline Si solar cells are proposed. The solar cells can greatly reduce thermalization loss. However, Si/SiO2 Si NC thin films exhibit low conductivity because of poor conductivity of SiO2 barrier layers. In this thesis, we created additional transportation paths by increasing the defects of barrier layers. We studied effects of the defects on the crystallization and dimension of Si NC thin films by Raman spectra and XRD. In addition, we analyzed the influences of the defects on optical properties of Si NC thin films by PL spectra. Finally, we discussed a possible carrier transportation mechanism from electrical results.