Elucidating the key role of fluorine in improving the charge mobility of electron acceptors for non-fullerene organic solar cells by multiscale simulations

In the last decade, fluorination has been successfully applied to organic semiconductor materials, especially to donor or acceptor materials for non-fullerene organic solar cells (OSCs). Currently, the power conversion efficiency based on these fluorinated materials is higher than that of the fullerene-based ones. Thus fluorination can down-shift the frontier molecular orbits, enhance inter/intramolecular interactions and reduce the Coulombic potential between holes and electrons. However, the key role of fluorine in improving the charge mobility of electron acceptors has yet to be systematically investigated. Here, we comprehensively explore the intermolecular interactions and electron mobilities in amorphous ITOIC and ITOIC-2F films by multiscale simulations. The simulations indicate that the electrostatically driven fluorine-pi (F-pi) interaction can exhibit a key role in increasing the intermolecular interactions and reducing the distance between the terminal groups of the fluorinated material ITOIC-2F. This phenomenon ultimately increases the intermolecular transfer integral and leads to an increase in electron mobility. Our work suggests that adding fluorine to the appropriate position of the phenyl ring can effectively inverse the electrostatic potential and produce intermolecular F-p interactions, which will be an effective way to improve the electron mobilities of the fluorinated electron acceptors for non-fullerene OSCs.