Heterointerface Screening Effects between Organic Monolayers and Monolayer Transition Metal Dichalcogenides

Abstract

The nature and extent of electronic screening at heterointerfaces and their consequences on energy level alignment are of profound importance in numerous applications, such as solar cells, electronics etc. The increasing availability of two-dimensional (2D) transition metal dichalcogenides (TMDs) brings additional opportunities for them to be used as interlayers in "van der Waals (vdW) heterostructures" and organic/inorganic flexible devices. These innovations raise the question of the extent to which the 2D TMDs participate actively in dielectric screening at the interface. Here we study perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) monolayers adsorbed on single-layer tungsten diselenide (WSe2), bare graphite, and Au(111) surfaces, revealing a strong dependence of the PTCDA HOMO-LUMO gap on the electronic screening effects from the substrate. The monolayer WSe2 interlayer provides substantial, but not complete, screening at the organic/inorganic interface. Our results lay a foundation for the exploitation of the complex interfacial properties of hybrid systems based on TMD materials.

Epitaxy of highly ordered organic semiconductor crystallite networks supported by hexagonal boron nitride

“…Heterointerfaces with vdW gap between OSCs and 2D materials have been first utilized employing graphene as a carrier injection layer between OSCs and metallic contacts7, and as vdW electrodes14. Besides graphene, layered semiconductors such as transition metal dichalcogenides have been used to form vdW heterostructures with OSCs915, even realizing atomically thin vdW p-n junctions11.…”

Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates

“…It is measured to be 3.73, 3.49, and 3.10 eV for PTCDA on SL WSe 2 /graphite (semiconducting), graphite (semimetallic), and Au(111) (metallic), respectively, as demonstrated in the scanning tunnelling spectroscopy (STS) results in Figure 7c, although the lattice parameters for these herringbone arrangements are very similar for the different substrates [70].Thus, the semiconducting 2D transition metal dichalcogenides (TMDs) layers can participate actively in hybrid organic−inorganic devices with tailored structures and properties. Figure 7b, because of the charge transfer from the Fe adatom to PTCDA molecules and concentration of the Coulomb charge.…”

“…The highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps of small organic molecules are dependent on the electronic screening effects from the substrate. It is measured to be 3.73, 3.49, and 3.10 eV for PTCDA on SL WSe2/graphite (semiconducting), graphite (semimetallic), and Au(111) (metallic), respectively, as demonstrated in the scanning tunnelling spectroscopy (STS) results in Figure 7c, although the lattice parameters for these herringbone arrangements are very similar for the different substrates [70].Thus, the semiconducting 2D transition metal dichalcogenides (TMDs) layers can participate actively in hybrid organic−inorganic devices with tailored structures and properties. …”

Charge-transfer states and optical transitions at the pentacene-TiO2interface

“…It is well-known that the band alignment can sometimes be a problem in DFT calculations for molecules on surfaces due to an unbalanced description of the different constituents. To investigate whether or not DFT qualitatively gives the correct band alignment for our system we look at a simple two-step procedure that has been successfully used to align molecular levels for surface adsorbates on metal and semiconductor surfaces [47][48][49]. In the first step individual shifts for the levels are computed in separate calculations for the bare substrate and the gas phase molecule.…”

“…)is the screened image charge, z is the height of the molecule above the surface and z 0 is the position of the image plane. To determine z 0 we fit E unocc D to match the exchange-correlation potential for the TiO 2 surface [47][48][49], giving us a plane 0.25 Å above the oxygen rows. We use the directionally averaged experimental  ¥ for bulk TiO 2 , that is 7.4  = , and consider the pentacene molecule to be located 2.8 Å above the surface, resulting in a shift of±1.08 eV.…”