Synthesis of Bithiophene-Based D-A(1)-D-A(2) Terpolymers with Different A(2) Moieties for Polymer Solar Cells via Direct Arylation

A series of bithiophene (2T)-based D-A(1)-D-A(2) terpolymers with different A(2) moieties were prepared via direct arylation reaction. In these terpolymers, pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) was selected as the first electron-accepting (A(1)) moiety, 2,1,3-benzothiadiazole (BT) or fluorinated benzothiadiazole (FBT) or octyl-thieno[3,4-c]pyrrole-4,6-dione (TPD) or 2,1,3-benzoselendiazole (SeT) was selected as the second electron-accepting (A(2)) moiety, while bithiophene with hexyl side chain was used as the electron-donating moiety. The UV-vis absorption, electrochemical properties, blend film morphology, and photovoltaic properties were studied to explore the effects of the A(2) moiety. It is shown that these terpolymer films exhibit broad absorption (350–1000 nm), full width at half-maximum of more than 265 nm and ordered molecular packing. Varying the A(2) moiety could affect the energy levels and blend film morphology leading to different polymer solar cell (PSC) performances of these (2T)-based D-A(1)-D-A(2) terpolymers. As a result, the highest J(sc) of 10.70 mA/cm(2) is achieved for Polymer 1 (P1) with BT as A(2) moiety, while the higher highest occupied molecular orbital (HOMO) level limits the open circuit voltage (V(oc)) and leads to a power conversion efficiency (PCE) of 3.46%.