Perylene bisimide(PBI) unit has been widely used to design conjugated materials, which can be used as electron acceptor in organic solar cells due to its strong electron-deficient ability. In this work, a conjugated polymer based on PBI dimer as monomer was designed, synthesized, and compared to the conjugated polymer containing single PBI as repeating units. The two conjugated polymers were found to have similar molecular weight, absorption spectra and energy levels. Density functional theory calculation revealed that the PBI dimer-based polymer exhibited highly twisted conjugated backbone due to the large dihedral angle between the two PBI units. The PBI-based polymers as electron acceptor were applied into polymer-polymer solar cells, in which PBI dimer-based polymer solar cells were found to show a high short circuit current density(J_(sc)= 11.2 m A·cm(-2)) and a high power conversion efficiency(PCE) of 4.5%. In comparison, the solar cells based on PBI-based polymer acceptor only provided a J_(sc) of 7.2 m A·cm~(-2) and PCE of 2.5%. The significantly enhanced PCE in PBI dimer-based solar cells was attributed to the mixed phase in blended thin films, as revealed by atom force microscopy. This study demonstrates that PBI dimer can be used to design polymer acceptors for high performance polymerpolymer solar cells. Perylene bisimide (PBI) unit has been widely used to design conjugated materials, which can be used as electron acceptor in organic solar cells due to its strong electron-deficient ability. In this work, a conjugated polymer based on PBI dimer as monomer was designed , synthesized, and compared to the conjugated polymer containing single PBI as repeating units. The two conjugated polymers were found to have similar molecular weight, absorption spectra and energy levels. Density functional theory calculating revealed that the PBI dimer-based backbone due to the large dihedral angle between the two PBI units. The PBI-based polymers as electron acceptor were applied into polymer-polymer solar cells, in which PBI dimer-based polymer solar cells were found to show a high short circuit current density ( (SC) = 11.2 m A · cm (-2)) and a high power conversion efficiency (PCE) of 4.5%. The solar cells based on PBI-based polymer acceptor only The significant enhanced PCE in PBI dimer-based solar cells was attributed to the mixed phase in blended thin films, as revealed by atom force microscopy. This study demonstrates that PBI dimer can be used to design polymer acceptors for high performance polymer polymer solar cells.