Book Description
Organic semiconductors have advantages over their inorganic counterparts including low cost, flexibility, and eco-friendliness. While organic semiconductors have interesting uses in devices such as solar cells, photovoltaic cells, and even flexible electronics, they are not competitive with inorganics due to their lower conductivity. One reason for this lower conductivity is due to their amorphous structure, making it difficult for electrons to tunnel from one adjacent molecule to the next. A possible method to increase the conductivity of organic semiconductors is crystallization via self-assembly. This work computationally examines the self-organization of an organic semiconductor, pentacene, on a simple and structurally similar surface, graphene. Ab initio calculations were used to determine the ground-state energy of a single pentacene molecule on a graphene sheet at various orientations, where the pentacene molecule is incrementally translated in the x and y directions at multiple angles. These energies are used to create potential energy maps of the system relative to the minima. This allows us to predict how pentacene organizes on graphene due to molecule-substrate interactions. The results in this study identify multiple configurations with relative energies less than that of room temperature, 27.8% of all considered. Additionally, 7.8% have a relative energy within 12.5 meV. Room temperature, 25 meV, is used as a comparative value to show how close (or far away) energy configurations are to each other. However, as it is more difficult for a molecule to thermally diffuse across a surface as all atoms would need to move in a uniform manner, a smaller energy range (12.5 meV) is also evaluated. These results demonstrate a need for an additional driving force (i.e., molecule-molecule interactions) for the self-organization of pentacene on graphene and provides a more complete understanding of the pentacene-graphene system.