First-principles calculations of metal-atom diffusion in oligoacene molecular semiconductor systems

Metal-atom diffusions in oligoacene model solid are studied by the first-principles density-functional calculations. We found that the high-electronegativity atoms such as Au produce hybridization-induced weak bonds with molecules and easily move in solid along the molecular axis direction with small potential barriers less than 0.4 eV, while the low-negativity atoms like Al are bound to molecules by relatively strong ionic-like interaction and are difficult to diffuse between molecules with large potential barriers around 0.9 eV. By analysing the changes of electronic structures and adiabatic potentials in various molecule configurations, we showed that the diffusion features, such as the diffusion path and the diffusion barrier, are determined at least by two factors: (i) the bonding between metal atoms and molecules and (ii) the elastic repulsion between metal atoms and neighboring molecules. These diffusion properties are expected common to most π-conjugated organic semiconducting molecular solids.

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► We study metal-atom diffusion in organic solids by the first-principles calculation.
► Diffusion behaviors are mainly determined by the chemical bonds with molecules.
► High-negativity atoms like Au easily diffuse reflecting weak covalent-like bonds.
► Low-negativity atoms like Al are difficult to diffuse due to strong ionic bonds.
► Elastic interaction also becomes a key factor to determine the diffusion paths.