Effect of fluorination on exciton binding energy and electronic coupling in small molecule acceptors for organic solar cells

Abstract

A detail study was performed to get deeper understanding of fluorination impact on intermolecular coupling and intermolecular interactions. Results showed that fluorine substitution plays an important role to modify the charge distribution or electrostatic potential as well non-covalent interaction between molecules. Dipole moment difference between ground and first excited states has increased while exciton binding energy has decreased by increasing the fluorine atoms. SM3 with asymmetric fluorine substitution showed higher transfer integral due to stronger attractive interactions. By proper substitution of fluorine atom, π-π stacking distance can be reduced to achieve higher electronic coupling. Substitution of fluorine atoms has increased the reorganization energy and non-linear optical response.