Synthesis of two-dimensional π-conjugated polymers pendent with benzothiadiazole and naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole moieties for polymer solar cells

Abstract

Four new 2D donor-acceptor conjugated polymers were designed and synthesized. These new polymers comprised fluorene- alt -triphenylamine or carbazole- alt -triphenylamine as the backbones, and pendants with 2,1,3-benzothiadiazole (BT) or naphtho[1,2- c :5,6- c ]bis[1,2,5]thiadiazole (NT) in a triphenylamine unit as the side groups. By changing the acceptor BT for a stronger electron-withdrawing unit of NT moiety in the side chain, the energy levels, absorption spectra, band gaps, and charge-transport abilities of the resultant polymers could be effectively tuned. Bulk heterojunction solar cells with these polymers as the electron donors and (6,6)-phenyl-C71-butyric acid methyl ester as the electron acceptor exhibited high open-circuit voltage (more than 0.8 eV). The power conversion efficiency can be improved from 1.37% to 3.52% by replacing the BT with an NT moiety, which indicates that introducing NT as the side-chain building block can be an effective strategy to construct efficient 2D conjugated polymers for PSCs.