Impact of Collective Electrostatic Effects on Charge Transport through Molecular Monolayers

A microscopic understanding of charge transport through molecule-based systems is essential for advancing the field of molecular electronics. In the present paper we highlight fundamental differences between devices with an individual molecule or a homogeneous monolayer as the active element. These differences arise from collective electrostatic effects that govern the electronic level alignment in monolayer-based devices, but are absent in the case of individual molecules. Employing density functional theory in conjunction with a Green’s function approach, we show that depending on the chemical nature of the employed molecules collective electrostatic effects can result in either a significant increase or a significant decrease of the current per molecule as a function of the packing density, in certain cases even resulting in a change in the transport polarity. Understanding the underlying principles also allows for designing molecules in which dipolar effects cancel, and thus, the transport characteristics of individual molecules and monolayers remain similar