Abstract - Reducing the recombination rate and increasing the photo-generation rate play a very significant role in improving the performance of the solar cells. In this research, AlGaAs has been used instead of GaAs in emitter layer with reduction in thicknesses of the base in order to decrease the recombination rate and increase the efficiency of the proposed solar cell. In addition, tunnel junction, buffer junction and BSF layers have been optimized to achieve higher efficiency. The efficiency can be improved by selecting optimal thickness of the materials because of the increase in photo-generation rate and absorption rate, improving transparency of the tunnel area and reducing the recombination rates of the solar cells. The results showed that after optimization, JSC (short circuit current density), VOC (open circuit voltage) and the η (conversion efficiency) of the solar cell are clearly increased. Also, the results of simulation were compared to the other designs in order to compare its performance. In the proposed structure, values of Voc= 2.52 V, Jsc= 29.09 mA/cm2, FF=86.49% and η= 62.04% (1 sun) are obtained under AM1.5G illumination.