Photoluminescence Quenching in WSe$_2$ via p-Doping Induced by Functionalized Rylene Dyes

TL;DR

This study shows that functionalizing WSe2 with an electron-deficient CN4PMI dye induces strong interfacial charge transfer and p-doping, leading to pronounced photoluminescence quenching. Through combined PL measurements and first-principles DFT analyses across multiple interface morphologies, the authors establish a type-II band alignment with a LUMO residing in the WSe2 gap, and demonstrate that the adlayer can drive either a reduced band gap or metallic behavior depending on adsorption geometry. The work provides a robust, design-oriented framework for tailoring TMD electronic structure via non-covalent organic functionalization, with implications for next-generation optoelectronic and quantum devices.

Abstract

Hybrid heterostructures combining transition metal dichalcogenides (TMDs) with light-harvesting dyes are promising materials for next-generation optoelectronics. Yet, controlling and understanding interfacial charge transfer mechanisms in these complex systems remains a major challenge. Here, we investigate the microscopic origin of photoluminescence (PL) quenching in $\text{WSe}_2$ functionalized with a novel, strongly electron-deficient perylene monoimide dye, $\text{CN}_4\text{PMI}$. Experimentally, the hybridization induces a $\sim$97\% PL quenching in $\text{WSe}_2$, confirming substantial static charge transfer and increased $p$-doping from the dye. To isolate the dominant electronic mechanism, we investigate from first principles various interface morphologies, including differing molecular orientations and layer thicknesses. Our density-functional theory results confirm that $\text{CN}_4\text{PMI}$ acts as a strong electron acceptor, inducing $p$-doping and forming a type-II level alignment with all considered configurations, giving rise to a small or vanishing band gap. Based on these findings, we attribute the observed PL suppression in $\text{WSe}_2$ to these strong electronic interactions with the dye. Our study provides a clear and validated strategy for tailoring the electronic structure of TMDs through targeted, electron-deficient organic functionalization.

Figures (4)

• Figure 1: Synthesis of CN4PMI.
• Figure 2: a) UV-Vis absorption (red curve) and emission (black curve) spectrum of the CN4PMI molecule b) PL spectra of a pristine WSe2 monolayer (blue curve) and the same sample after hybridization with CN4PMI (red curve), both exited with the same laser power density of 5000 W/cm$^2$ and wavelength of 633 nm.
• Figure 3: Ball-and-stick representations, created with the visualization software VESTA,Momma-db5098 of the unit cells of the investigated hybrid interfaces, including a single CN4PMI adsorbed flat on a) monolayer, b) bilayer, and c) trilayer WSe2, d) CN4PMI molecules adsorbed on WSe2 monolayer and a single CN4PMI molecule adsorbed on monolayer WSe2 with an angle e) $\alpha=22^{\circ}$ and f) $\beta = 43^{\circ}$. C, N, O, H, W, and Se atoms are depicted in black, blue, red, white, gray, and green, respectively.
• Figure 4: Projected densities of state (PDOS) of CN4PMI adsorbed on WSe2 in all considered configurations: a) CN4PMI:1L, b) CN4PMI:2L, c) CN4PMI:3L, d) 2(CN4PMI):1L, e) CN4PMI(22$^{\circ}$):1L, and f) CN4PMI(43$^{\circ}$):1L. The contributions from molecule (purple) and WSe2 (orange) in the heterostructure are indicated by solid curves, while the results obtained for the isolated constituents are plotted by dashed curves (CN4PMI in magenta and WSe2 in light orange). A 50 meV Lorentzian broadening is applied to all curves for visualization. The energy scale is referenced to the vacuum level, and the Fermi energy (E$_F$) is marked by a dotted bar.