Benzodithiophene/Benzothiadiazole-Based ADA-Type Optoelectronic Molecules: Influence of Fluorine Substitution

Fluorination on conjugated components is one of popular strategies to modify organic optoelectronic materials.Following the research of a benzodithiophene/benzothiadiazole ADA-type optoelectronic molecule, two benzothiadiazole (BT) units were fluorinated with different numbers and positions, and the change in basic properties and performances for field-effect transistors and organic solar cells was investigated.It was found that when the F-substitution number increases, the molecule enhances thermal stability, decreases solubility, lowers HOMO and LUMO energy levels, but almost does not alter light absorption range.Furthermore, investigations on organic field-effect transistors found the molecular hole mobility reduces with only one F-substituent at outer position of BT units, while increases up to 0.27 cm 2 •V -1 •s -1 with two F substituents on BT units.However, when these materials are applied in organic solar cells, the fluorinated ones enhance open-circuit voltage, but deteriorate active layer morphology, finally leading to decrease in short-circuit current and device efficiency.