Development of New Photovoltaic Conjugated Polymers Based on Di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole: Benzene Ring Extension Strategy for Improving Open-Circuit Voltage

We have synthesized a series of novel di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP)-based conjugated polymers for organic photovoltaic devices. We first introduced DBTP moiety as an electron donating part in the conjugated polymer system to improve the open-circuit voltage (Voc) in photovoltaic properties. The DBTP backbone has a fused ring structure with extended benzene rings at the end of the 4H-dithieno[3,2-b:2′,3′-d]pyrrole (DTP) moiety. The synthesized DBTP-based polymers effectively enhanced Voc compared to DTP-based polymers by decreasing the highest occupied molecular orbital (HOMO) energy levels of polymers without damaging other photovoltaic parameters. The alternation of DBTP and 3,6-dithien-2-yl-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-dione (DTDPP) formed a promising donor polymer, PDBTP4, exhibiting an excellent molar absorption coefficient of 17 600 L cm–1 mol–1 at the absorption maximum of 719 nm and a broad absorption covering 550–850 nm. PDBTP4:[6,6]-phenyl-C71-butyric acid methyl ester (P...