Calculation of Electronic Structure and Transport in Polymers

Organic thin-film transistors producible by low-cost roll-to-roll manufacturing processes seem to be highly promising for flexible electronics. Therefore, high mobility semiconducting polymers with ambient stability, good solubility and film-forming properties are needed. Our study is turned to the calculation of the electronic transport properties through polymers consisting of conjugated thiophene based donor units and di-ketopyrrolo-pyrrol based acceptor units. The structure and electronic properties of thiophene-based molecular stacks is studied by means of quantum- mechanical calculations. We demonstrate how the functionalization of thiophenes can increase the dispersion interaction and promote the parallel- stacked arrangement of the molecules, which is essential to get efficient charge transport channels in the direction perpendicular to the plane of the thiophene rings. Moreover, we found that the π-π-stacking is the main driving force in the self-assembly of the molecules in the film. These results are the basis for further studies of the hopping transport properties of this promising organic semiconducting material.
For the description of the electronic transport we apply a Greens function method, including Coulomb and inelastic tunneling to a simple one-particle hopping Hamiltonian by calculating the matrix elements through overlap integrals of orbitals obtained from density-functional calculations.