Large Induced Interface Dipole Moments without Charge Transfer: Buckybowls on Metal Surfaces

Charge carrier injection barriers at interfaces are crucial for the performance of organic electronic devices. In this respect, tuning the electronic interface potential or, in case of the metallic electrode, the work function for electronic level alignment is crucial. However, poor control over the interface structure and the work function of the combined materials is an obstacle for better device performance. Here we show that bowl-shaped molecules, based on buckminsterfullerene, induce very large interface dipole moments of up to 8.8 D on a copper surface. It is shown experimentally and theoretically that charge transfer between both components is negligible. The origin of the large dipole moments is revealed via dispersion-enabled density functional theory, displaying a strong rearrangement of charge in the metal underneath the molecular adsorbate.