Interactions at the interface between aluminum and polythiophene are investigated by means of model molecules. The model systems are studied with ab initio Hartree-Fock calculations, where core electron binding energies are determined by the delta self-consistent-field method. The theoretical results are compared to reported experimental core-level X-ray photoelectron spectroscopy data of the interface. A model system in which two aluminum atoms are bound to the alpha-carbons of a thiophene ring is found to give chemical shifts in agreement with those observed upon interface formation.