Synthesis of bithiophene-based D-A 1 -D-A 2 terpolymers with different A 2 moieties for polymer solar cells via direct arylation

Abstract

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 Jsc 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%.