Synthesis and photovoltaic properties of a donor-acceptor polymer containing both dithieno[3,2-b:2′,3′-d]pyrrole and fluorene as donor units

A new donor-acceptor polymer (PDTPDBF), containing both dithieno[3,2-b:2′,3′-d]pyrrole (DTP) and fluorene as electron-donating units and benzo-2,1,3-thiadiazole (BT) as electron-accepting unit, was synthesized by Suzuki coupling reaction. Its optical, thermal, electrochemical and photovoltaic properties have been investigated. Compared with typical DTP-based donor-acceptor polymers, PDTPDBF showed a distinct low HOMO level (−5.47 eV). Theoretical calculation attributed this low-lying HOMO level to both the weaker electron-donating ability of the fluorene unit and the moderately twisted conformation between the fluorene unit and the BT unit. Polymer solar cells (PSCs) based on PDTPDBF and PC71BM (1:2, w/w) exhibited an open circuit voltage of 0.84 V and a power conversion efficiency (PCE) of 4.2%, both of which are relatively high values for DTP-based photovoltaic polymers.