Bright hybrid excitons in molecularly tunable bilayer crystals

TL;DR

This paper demonstrates the creation of hybrid excitons in molecularly tunable bilayer crystals, combining molecular and atomic layers to achieve customizable optoelectronic properties with potential for advanced quantum materials.

Contribution

It introduces a new class of hybrid bilayer crystals with tunable excitonic properties, synthesized by stacking molecular crystals on 2D monolayers, enabling bottom-up design of quantum materials.

Findings

Hybrid excitons exhibit bright photoluminescence with near-unity polarization.

Exciton energies and intensities are tunable via composition modifications.

Theoretical calculations confirm lattice-scale hybridized band structure.

Abstract

Bilayer crystals, built by stacking crystalline monolayers, generate interlayer potentials that govern excitonic phenomena but are constrained by fixed covalent lattices and orientations. Replacing one layer with an atomically thin molecular crystal overcomes this limitation, as diverse functional groups enable tunable molecular lattices and interlayer potentials, tailoring a wide range of excitonic properties. Here, we report hybrid excitons in four-atom-thick hybrid bilayer crystals (HBCs), directly synthesized with single-crystalline perylene diimide (PDI) molecular crystal atop WS2 monolayers. These excitons arise from a hybridized bilayer band structure, revealed by lattice-scale first-principles calculations, inheriting properties from both monolayers. They exhibit bright photoluminescence with near-unity polarization above and below the WS2 bandgap, along with spectral signatures of exciton delocalization, supported by theory, while their energies and intensities are tuned by modifying the HBC composition by synthesis. Our work introduces a molecule-based 2D quantum materials platform for bottom-up design and control of optoelectronic properties.