Synthesis of donor-acceptor copolymers based on anthracene derivatives for polymer solar cells

A series of narrow band gap donor acceptor type conjugated copolymers based on 2,6-linked anthracene derivatives are synthesized via Suzuki copolymerization. The resulting copolymers typically exhibit dual absorption characteristics in both solution and as thin films with optical band gaps in the range of 1.85- 2.13 eV. By varying the substitutions from alkyloxy to aromatic thienyl and phenyl groups in the 9,10-positions of the anthracene unit, the constructed two-dimensional 2,6-linked anthracene structures lead to broader absorption, lower-lying highest occupied molecular orbitals, as well as improved charge carrier mobilities of the resulting copolymers relative to the alkyloxy side chain substituted counterparts. Additionally, it was found that the sizes of the substitutions in the benzo[c][1,2,5]thiadiazole acceptor also play an important role in the optoelectronic properties of these anthracene based conjugated copolymers. The best polymer solar cell device with a power conversion efficiency of 4.34% and a high open circuit voltage of 0.98 V was realized based on the resulting materials. Our results indicate that substantial optimization in the sizes and patterns of substitutions of both the 2,6-linked anthracene donor and benzo[c][1,2,5]thiadiazole acceptor may potentially lead to high performance narrow band gap copolymers for solar cell applications.