- The performance of the ZnMgO/CIGSSe heterojunction solar cell is addressed in this article. Different structures are designed using different materials to improve their parameters. The AFORS-HET simulation tool is used here to justify the photovoltaic results of the reference SLG/(Ni/Al)/ZnMgO:Al/ZnMgO/CIGSSe/Mo solar cell. Later, cuprous oxide (Cu2O) is added to construct a single graded solar cell as an electron reflected-hole transport layer (ER-HTL) between the back metal contact and the CIGSSe layer in the reference device. Furthermore, in the single-graded device, magnesium doped cerium oxide (CeMgO2) as a hole reflected-electron transport layer (HR-ETL) is put between the ZnMgO buffer and the CIGSSe absorber layer to make a double-graded proposed solar cell. The photogenerated recombination losses are get diminished by this double-graded proposed SLG/(Ni/Al)/ZnMgO:Al/ZnMgO/CeMgO2/CIGSSe/Cu2O/Mo solar cell and improved the photovoltaic parameters of the cell such as VOC = 858.3 mV, JSC = 40.18 mA/cm2, FF = 83.42% and η = 28.77%.