Making solar cell with thinner wafer could reduce the material cost. However, with the thinning of the wafer thickness, the energy conversion efficiency (Eff) is also reduced. In this study, single crystalline silicon wafer with different thickness (180 µm, 130 µm, 100 µm, and 70 µm) was used. The Eff was varied from 17.35% to 16.98% as the decreasing of wafer thickness. This was due to the short circuit current density losing. The thinner wafer had less light absorption and caused Jsc reduction from 37.39 mA/cm2 to 36.83 mA/cm2. For improving the efficiency, selective emitter structure was used. The Eff could be increased to 17.48%, which was comparable to convention solar cell, as the wafer thickness was only 70 µm.