Evidence for Hybrid Inorganic–Organic Transitions at the WS₂/Terrylene Interface

Abstract

The realization of the potential of hybrid inorganic organic systems requires understanding of the coupling between the constituents: its nature and its strength. We report on the observation of hybrid optical transitions in the monolayer WS2/terrylene hybrid. We employ first‐principle calculations, linear optical and transient absorption spectroscopy to investigate the optical spectrum of the hybrid, which exhibits a new transition that does not appear in the constituents’ spectra. Calculations indicate type II level alignment, with the highest occupied level of terrylene in the gap of WS2. Exploiting state‐resolved transient absorption, we selectively probe the response of the hybrid interface to optical excitation. The dynamics reveal rapid hole transfer from WS2 to the terrylene layer, with a decay time of 88 ps. This hole transfer induces a bleach of the hybrid transition, which indicates that terrylene contributes to its initial state. Based on this, the hybrid resonance energy, and on our calculations, we assign the hybrid feature to a transition from the highest occupied molecular orbital of terrylene to the conduction band of WS2 close to the Γ point. Our results indicate the conditions for strong electronic coupling are met in this hybrid system.This article is protected by copyright. All rights reserved.

Spin-Polarized Charge Separation at Two-Dimensional Semiconductor/Molecule Interfaces

“…In addition to the quenching of the MoSe 2 A-exciton peak, the PL of MoSe 2 /H 2 Pc contains a low-energy feature at h ν <1.5 eV. This peak cannot be attributed to increased emission from minority defects in the MoSe 2 monolayer, as the adsorption of phthalocyanine molecules on TMDC monolayers is known to remove in-gap states. , A possible origin of this feature is the emission from hybrid interlayer excitons, which have been observed before in other organic/TMDC heterostructures. − This interpretation is supported by the observation of ultrafast hole transfer from photoexcited MoSe 2 to H 2 Pc, as detailed below.…”

“…It is important to note that an electron–hole pair in a TMDC monolayer, heterobilayer, or across TMDC monolayer/molecule interface − is predominantly an exciton. The quasiparticle energy level diagrams shown in Figure b are modified by the difference in binding energies of intralayer and interlayer excitons.…”

Magnification of Plasmon Resonances in Monolayer MoS2 via Conjugated Molecular Adsorbates

“…Tetracene is a member of the oligoacene family and is characterized by an anisotropic geometry. Pyrene, in contrast, is more isotropic and is often used in first-principles studies − , as a prototype for larger conjugated compounds such as (functionalized) rylenes that favorably adsorb on TMDCs. ,,, These compounds exhibit a weak coupling with MoS 2 as extensively discussed in previous work specifically dedicated to this aspect . In particular, the band structure and the density of states of the TMDC are negligibly affected by the presence of the physisorbed molecule, and apart from hybridization effects that are ruled by specific conditions, the electronic structure of the interface is essentially a superposition of the features of its constituents. − ,, For this reason, in optical absorption, specific transitions within the molecular frontier orbitals can be targeted, e.g., by a laser pulse …”

“…First of all, to the best of our knowledge, there is no evidence that small molecules such as pyrene and tetracene can be adsorbed on TMDCs in a stable manner: only larger acenes such as pentacene and extended rylenes such as terrylene have been demonstrated to form stable interfaces with TMDCs. 46,53,55 Second, in realistic samples, intrinsic effects such as the density of the molecules on the substrate, the morphology of their clusters, and the thickness of their layers as well as extrinsic factors such as temperature, pressure, and surface roughness play a decisive role in determining the characteristics of the interface. All of these aspects should be carefully addressed for a reliable comparison with experiments, but they go beyond the scope of the present work.…”

“…The goal of this study is to understand, in a proof-of-principle fashion, whether and how the loss-function resonances of MoS 2 are modified by the presence of physisorbed conjugated molecules. As a matter of fact, the chosen carbon-based compounds do not enable the formation of stable interfaces on TMDCs in contrast to larger related molecules already employed in experimental works. ,,− By exploring different configurations in which the moieties are systematically rotated with respect to the direction of the transferred momentum q , we analyze energy, intensity, and dispersion of the plasmon resonances arising at these hybrid interfaces. We find significant magnification induced by the molecular adsorbates of selected maxima in the loss function of MoS 2 , which is accompanied by minor variations in terms of energy and q -dependent dispersion.…”