Structural and energetic properties of P3HT and PCBM layers on the Ag (111) surface

The structural and energetic properties of poly(3-hexyl-thiophene) (P3HT) and 6,6-phenyl C61 butyric acid methyl ester (PCBM) monolayers and multilayers on the Ag(1 1 1) surface are investigated using classical force fields and molecular dynamics simulations. The results demonstrate that P3HT has a stronger interaction with the substrate, while PCBM exhibits larger monolayer formation energy due to stronger intermolecular interactions. In addition, PCBM prefers a tail-up conformation by orienting the phenyl and butyric acid methyl ester groups away from the surface, thus favoring a denser packing, while relaxation of intermolecular order in P3HT is found to initiate above 450 K. For the simulations a new parameterization of the General Amber Force Field involving dihedral angles and interactions with the Ag(1 1 1) substrate was developed. The new parameters were validated successfully against available crystal structures and ab initio data.