Near- and Far-Field Effects on Molecular Energy Level Alignment at an Organic/Electrode Interface

Abstract

We investigate the evolution of the interfacial electronic structure at the interface of (sub)monolayer vanadyl naphthalocyanine (VONc) on highly oriented pyrolytic graphite (HOPG). Both the vacuum level and molecular energy levels show a significant but fundamentally different dependence on coverage, resulting in an overall change of the ionization potential with coverage. We use a simple model to show how this effect arises from the differential sensitivity of these levels to the near- and far-field properties of the dipole-layer-generated interfacial electric potential. These results help to unravel the electronic structure at organic/electrode interfaces, with direct implications for organic electronic devices.

Interplay of local and global interfacial electronic structure of a strongly coupled dipolar organic semiconductor

“…Molecular dipole moment [23,24], electron transfer from surface to molecule and chemisorption [25,26] as well as push-back effects [27] can all contribute to the work function change upon film growth. The work function evolution gives thus a first clue to the surface/molecule interactions.…”

“…Structure is often inferred spectroscopically [11][12][13], an approach that works well for highly ordered organic thin films such as e.g. C 60 on Cu (111) [14] or PTCDA on Ag (111) [9].…”

Theoretical investigation of molecular excited states in polar organic monolayers via an efficient embedding approach

“…2, we report the workfunction shift (computed with the SPICE method using Eq. 1) as a function of the VONc coverage and compare it with experimental data for VONc on highly oriented pyrolytic graphite [38].…”

“…To this end, we apply the SPICE method to study the depolarization effect and the single-molecule excitation spectrum in three typical SAMs with significant dipole moment and employed in molecular electronic and optoelectronic applications, namely those of vanadyl naphthalocyanine (VONc) [38], mercaptobiphenyl [39,40], and tris-(8-hydroxyquinoline) aluminum (AlQ 3 ) [41] (for the latter both the facial and the meridional configurations were considered). The geometries and the unit cells of the all considered systems are reported in Fig.…”

“…1. VONc has been largely investigated from an experimental point view [29,36,38,42] due to its large dipole moment perpendicular to a large macrocyle; mercaptobiphenyl has been the subject of many theoretical studies as a model system of SAM/metal interfaces [10,16,39,40]; AlQ 3 is a molecule often employed in the realization of optoelectronic devices [43][44][45][46][47].…”