Molecular Alignment and Electronic Structure of N,N′-Dibutyl-3,4,9,10-perylene-tetracarboxylic-diimide Molecules on MoS₂ Surfaces

Abstract

The molecular orientation of organic semiconductors on a solid surface could be an indispensable factor to determine the electrical performance of organic-based devices. Despite its fundamental prominence, a clear description of the emergent two-dimensional layered material-organic interface is not fully understood yet. In this study, we reveal the molecular alignment and electronic structure of thermally deposited N,N'-dibutyl-3,4,9,10-perylene-dicarboximide (PTCDI-C4) molecules on natural molybdenum disulfide (MoS) using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The average tilt angle determination reveals that the anisotropy in the π* symmetry transition of the carbon K-edge (284-288 eV range) is present at the sub-monolayer regime. Supported by ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), and resonant photoemission spectroscopy (RPES) measurements, we find that our spectroscopic measurements indicate a weak charge transfer established at the PTCDI-C4/MoS interface. Sterical hindrance due to the C4 alkyl chain caused tilting of the molecular plane at the initial thin film deposition. Our result shows a tunable interfacial alignment of organic molecules on transition metal dichalcogenide surfaces effectively enhancing the electronic properties of hybrid organic-inorganic heterostructure devices.

Leveraging Molecular Properties to Tailor Mixed-Dimensional Heterostructures beyond Energy Level Alignment

“…Polarized Raman spectroscopy can provide qualitative information about molecular orientation, , and more quantitative information can be extracted with some knowledge of the molecular Raman tensor using azimuthally and radially polarized light . Film structure can also be characterized by X-ray techniques such as diffraction, grazing-incidence wide-angle X-ray scattering (GIWAXS), and near-edge X-ray absorption fine structure (NEXAFS), , or by scanning probe techniques such as scanning tunneling microscopy (STM) or atomic force microscopy . Many of these tools also provide complementary information about the electronic structure of the heterojunction and thus should be used in combination to more fully elucidate the links between the physical structure of thin films and the electronic properties of the constituent materials.…”

Structure-Dependent Electron Affinities of Perylene Diimide-Based Acceptors

“…It is generally observed that the molecules with a longer alkyl chain preferentially grow with an end-on orientation. In PTCDI derivatives, R = C 4 H 9 (C4) or longer may have an end-on orientation on any substrate. , The C1 molecule is an intermediate case that has a face-on orientation on graphene (or HOPG) and a mixture of face-on and end-on orientations on SiO 2 . It is interesting to note that the surfaces of C0 and C1 do not correlate with the molecular boundary in the crystal structures (Figure S1).…”

Linking optical spectra to free charges in donor/acceptor heterojunctions: cross-correlation of transient microwave and optical spectroscopy

“…[48][49][50][51] CTEs have also been identified in numerous TMDC heterojunctions with small molecules. [52][53][54] In organic donor/acceptor heterojunctions, CTEs have been observed in sensitive sub-bandgap absorption and photoluminescence measurements, along with some evidence of very small photocurrents in quantum efficiency measurements of photovoltaic devices. 55 While some CTEs may dissociate into free carriers, a number of analyses suggest that such CTEs can inhibit free charge generation and reduce the voltage of OPVs.…”