Boosting the electron mobilities of dimeric perylenediimides by simultaneously enhancing intermolecular and intramolecular electronic interactions

For organic solar cells using perylenediimide (PDI) derivatives as electron acceptors, bulky substitution and covalent dimerization (or multimerization) are often used to reduce the intermolecular pi-pi interaction to prevent PDI from forming oversized phase separation with electron donors. Here, we have investigated the influence of different dimerization and alkylation processes on the molecular packing and electron transport properties of PDI derivatives by means of molecular dynamics simulations in combination with electronic structure calculations and kinetic Monte Carlo simulations. The results suggest that like branched alkyl substitution, dimerization can effectively prevent pi-pi aggregation. Particularly, the pi-pi stacking is mostly prohibited for the bay C-C dimeric PDIs, even with linear alkyl substituents. More importantly, different from the case of bulky substitution, dimerization will hardly reduce short intermolecular contacts between PDI units. Unexpectedly, the electron mobilities of dimeric PDIs are always higher than those of the parent monomeric PDIs due to extra intramolecular electronic connections. Owing to simultaneously enhanced intermolecular and intramolecular interactions, the electron mobility of the bay C-C dimeric PDI with linear alkyl chains is increased by nearly 20 times with respect to the monomeric PDI with branched alkyl chains. Our work demonstrates that high charge mobilities along with suppressed pi-pi aggregation can be achieved by properly tailoring both the modes of dimerization and substitution.