Although pi-conjugated, organic semiconductors have been successfully tested in several electronic devices, a full understanding of the precise nature of the underlying charge migration mechanisms is still lacking. In such systems, charge carrier mobilities are dramatically influenced by the structural fluctuations of the molecular stacks, which makes it necessary to take dynamic effects into account beyond purely perturbative treatments. As a result of this strong coupling of the electronic structure to dynamic degrees of freedom, charge transport cannot be described in terms of fully coherent or fully incoherent microscopic mechanisms within the molecular devices' operating temperature range (250 K to 350 K). In our studies, based on accurate and extensive benchmark calculations, three different theoretical methodologies are extended and applied to investigate the charge transport characteristics of molecular model systems. The migration of the charge carrier is simulated by means of kinetic Monte Carlo techniques and a quantum dynamical real-time, real-space propagation of its wave function. Herewith, charge carrier mobilities are computed for highly ordered molecular systems of different complexity consisting of coronene, pentacene, or novel, promising near-infrared absorber materials. The conduction process in molecular junctions is investigated in terms of current-voltage characteristics by using non-equilibrium Green function techniques applied on the Holstein-Peierls Hamiltonian. The theoretical investigations open the possibility to achieve quantitative comparisons to transport experiments and to treat on a first-principle basis charge transport in organic semiconducting materials.
Although pi-conjugated, organic semiconductors have been successfully tested in several electronic devices, a full understanding of the precise nature of the underlying charge migration mechanisms is still lacking. In such systems, charge carrier mobilities are dramatically influenced by the structural fluctuations of the molecular stacks, which makes it necessary to take dynamic effects into account beyond purely perturbative treatments. As a result of this strong coupling of the electronic structure to dynamic degrees of freedom, charge transport cannot be described in terms of fully coherent or fully incoherent microscopic mechanisms within the molecular devices' operating temperature range (250 K to 350 K). In our studies, based on accurate and extensive benchmark calculations, three different theoretical methodologies are extended and applied to investigate the charge transport characteristics of molecular model systems. The migration of the charge carrier is simulated by means of kinetic Monte Carlo techniques and a quantum dynamical real-time, real-space propagation of its wave function. Herewith, charge carrier mobilities are computed for highly ordered molecular systems of different complexity consisting of coronene, pentacene, or novel, promising near-infrared absorber materials. The conduction process in molecular junctions is investigated in terms of current-voltage characteristics by using non-equilibrium Green function techniques applied on the Holstein-Peierls Hamiltonian. The theoretical investigations open the possibility to achieve quantitative comparisons to transport experiments and to treat on a first-principle basis charge transport in organic semiconducting materials.
