We report for the first time a simple optimization of triple-junction solar cell nc-Si:H/a- Si:H/a-SiGe:H using computer modeling and Robust Design. Firstly we performed a computer modeling of solar cell by wxAMPS software. Subsequently, we investigated the parameters of the solar cell layers and the effect of the solar cell efficiency using Robust Design via Taguchi method, ANOVA and additive model. The results show that the a-Si:H middle absorber cell has the highest contribution of solar cell efficiency at 40.87% and the nc-Si:H n-back layer cell has the second highest contribution of solar cell efficiency at 31.15%. Moreover, the optimum condition for triplejunction solar cell is A2 B1 C2 D2 with solar cell efficiency at 15.73%. These results indicate that Robust Design succeeded predicting the best condition for optimizing triple-junction solar cell nc- Si:H/a-Si:H/a-SiGe:H.