Theoretical investigations of the aluminum/polythiophene interface

Interactions at the interface between aluminum and polythiophene are studied theoretically using ab initio Hartree-Fock and Møller-Plesset perturbation theories as well as semiempirical techniques. Aluminum is found to interact strongly with the polythiophene chain. The fundamental interaction unit corresponds to an aluminum dimer (Al₂) bound to a single thiophene ring. This type of interaction strongly modifies the geometrical structure of the polymer chain and induces localization of the π-electron system. The calculated charge transfer between aluminum and the thiophene system is found to be in good agreement with the charge transfer deduced from experimental core level spectra of the aluminum/ polythiophene interface. A detailed analysis of the electronic structure, including the correlation effects, of a model system (Al₂ interacting with α-trithienylene) is performed. Higher concentrations of aluminum atoms on a polythiophene chain results in the formation of additional Al₂-thiophene complexes. Within the first monolayer, clustering of aluminum on polythiophene is shown to be energetically unfavorable.