A new n-type polymer, PF3N-2TNDI, with high electron mobility, is developed as efficient cathode interfacial material and interconnecting layer (ICL) for constructing high-performance tandem organic solar cells. Tandem cells employing the ICL with structure of PF3N-2TNDI/Ag/PEDOT:PSS achieve a high power conversion efficiency (PCE) of 11.35%. More over, flexible tandem cells with PCE over 10% are also demonstrated.