In order to gain insight into the nature of interaction modes of the ion-pairs in solution, molecular dynamics (MD) simulations using the generalized Amber force field (GAFF) were performed. The MD simulations are carried out with a simulation box that contains 20 molecules, 10 of them being P3HT cations and the other 10 F 4 TCNQ anions. Each P3HT polymer contains 7 monomer thiophenes units along with the hexyl side chains (see Fig. for initial input molecular configuration). The simulation has been performed in a cubic box of 10 × 10 × 10 nm 3 containing chlorobenzene as solvent. There were 5103 chlorobenzene molecules contained in the simulation box. The NPT condition is set to be T = 298 K and P = 1 atm. After equilibration, the MD trajectory runs for 100 ns. For each time snapshot, we pick the P3HT cations and locate the closest two F 4 TCNQ anions for every P3HT cation, using their center of mass distance of the non-hydrogen atoms.