A comprehensive study of high efficiency In0.46Ga0.54N/Si tandem solar cell is presented.A tunnel junction (TJ) was needed to interconnect the top and bottom sub-cells.Two TJ designs,integrated within this tandem:GaAs(n+)/GaAs(p+) and In0.5 Ga0.5N(n+)/Si(p+) were considered.Simulations of GaAs(n+)/GaAs(p+) and In0.5Ga0.5N (n+)/Si(p+) TJ I-V characteristics were studied for integration into the proposed tandem solar cell.A comparison of the simulated solar cell I-V characteristics under 1 sun AM1.5 spectrum was discussed in terms of short circuit current density (JSC),open circuit voltage (VOC),fill factor (FF) and efficiency (η) for both tunnel junction designs.Using GaAs(n+)/GaAs(p+) tunnel junction,the obtained values of JSC =21.74 mA/cm2,VOC =1.81 V,FF =0.87 and η=34.28％,whereas the solar cell with the In0.5Ga0.5N/Si tunnel junction reported values of JSC =21.92 mA/cm2,VOC =1.81 V,FF =0.88 and η =35.01％.The results found that required thicknesses for GaAs(n+)/GaAs(p+) and In0.5Ga0.5N (n+)/Si(p+) tunne1 junctions are around 20 nm,the total thickness of the top InGaN can be very small due to its high optical absorption coefficient and the use of a relatively thick bottom cell is necessary to increase the conversion efficiency.