In this paper, the CuInGaSe2 based solar cell optimization has been established. We have simulated the structural strain effect. The effect of gallium concentration on the optical properties and the quantum external efficiency EQE was investigated. We also optimized the concentration x at low defect densities. The optimal gallium concentration is 0.30. We obtained an efficiency of the CuIn0.70Ga0.30Se2 absorber solar cell around 24% with a strain ɛ = 0.64% and material defects densities equal to 1.2x1015cm−3. This work has been validated by theoretical and experimental studies. This study allows us to find a compromise between concentration x and defect concentrations in order to improve the performance and high efficiency of the solar cell.