By combining optical and drift-diffusion models, a comprehensive simulation of power conversion efficiency of tandem solar cells is presented. To obtain consistent current–voltage characteristics of polymer tandem solar cells, the model takes into account correct description of organic–metal interfaces and organic semiconductor physics, in order to include the effect of interfaces and energetic disorder. A generalized methodology is developed to obtain the current–voltage characteristics of polymer tandem solar cells, which fully accounts for the interplay between the two subcells. The model is applied to the tandem cell with different commercially available polymers and for different subcell thicknesses and interconnection architectures. Based on the results of this model, it will be possible to design and optimize tandem structures toward higher efficiencies. Finally, it is concluded that the parallel configuration shows the highest performance over all studied cell structures.