Synthesis, Characterization, and Photovoltaic Properties of Carbazole-Based Two-Dimensional Conjugated Polymers with Donor-π-Bridge-Acceptor Side Chains

A series of carbazole-based narrow-band gap polymers with two-dimensional donor-pi-bridge-acceptor (D-pi-A) structures were synthesized and characterized for use in polymer bulk heterojunction solar cells. These D-pi-A side-chain polymers were obtained through the Knoevenagel condensation between the aldehyde-containing precursor polymers and the corresponding acceptors. The resulting polymers have good solubility in common organic solvents and excellent thermal properties. The effects of the alkyl side chains and different dye contents on optical properties, electronic structures, charge-transporting ability, and device performance of these polymers were investigated. By blending these polymers as light-harvesting electron donors with (6,6)-phenyl-C-71-butyric acid methyl ester (PC71BM) electron acceptors in bulk heterojunction solar cells, high power conversion efficiency (PCE), as high as 4.47%, could be achieved.