The effect of the fluorine loading on the optoelectronic and photovoltaic properties of (X-DADAD-)n-type donor-acceptor copolymers with the benzothiadiazole A units

We synthesized and investigated novel low bandgap (X-DADAD-)(n)-type donor-acceptor copolymers comprising non-fluorinated 2,1,3-benzothiadiazole (BT) and the fluorinecontaining 5,6-difluoro-2,1,3-benzothiadiazole (ffBT) as the electron acceptor blocks (A). The introduction of fluorine substituents was shown to influence optical, electrochemical, and morphological properties of the polymers, as well as their photovoltaic performance. Optimized bulk heterojunction solar cells based on the fluorine-loaded polymer P2 showed improved characteristics (efficiency of 5.2%) as compared to the reference cells based on the non-fluorinated polymer P1 (efficiency of 4.4%).