High-performance fluorine-containing BDT-based copolymer for organic solar cells with a high open circuit voltage

Abstract

A new donor–acceptor (D-A) conjugated copolymer (PBDTT(ff)-ttTPD) based on fluorine-substituted benzodithiophene (BDT) and 6-alkylthienothienyl thieno[3,4-c]pyrrole-4,6-dione (ttTPD) has been synthesized via a Stille cross-coupling reaction. As a control, the nonfluorinated BDT-based ttTPD copolymer (PBDTT-ttTPD) was also synthesized by using the same polymerization method. The number-average molecular weights (Mn) of PBDTT(ff)-ttTPD and PBDTT-ttTPD were found to be 48,000 g/mol (Đ = 2.2) and 43,000 g/mol (Đ = 2.1), respectively. The HOMO levels of PBDTT(ff)-ttTPD and PBDTT-ttTPD were calculated to be −5.65 and −5.45 eV, respectively. The inclusion of fluorinated BDT units is a very effective approach to lowering the polymer's HOMO level. The SCLC mobilities of PBDTT(ff)-ttTPD and PBDTT-ttTPD were determined to be 5.9 × 10−4 and 3.0 × 10−4 cm2/Vs, respectively. Polymer solar cell devices prepared with PBDTT(ff)-ttTPD and PBDTT-ttTPD as their active layers were found to exhibit power conversion efficiencies of 7.45 and 6.79% with open circuit voltages of 0.98 and 0.84 V, respectively. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2506–2512