A power conversion efficiency of up to 8.91% is obtained for a solution-processed polymer tandem solar cells based on a large-bandgap polymer, poly(4,4-dioctyldithieno(3,2-b:2,3-d)silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl) with a polymeric interconnecting layer to electrically connect the front and rear subcells, demonstrating that proper device and interface engineering are can improve the performance of polymer tandem solar cells.