Hybrid Frenkel-Wannier excitons facilitate ultrafast energy transfer at a 2D-organic interface

TL;DR

This study reveals the formation of hybrid Frenkel-Wannier excitons at TMD/OSC interfaces, combining experimental ultrafast microscopy and theoretical modeling to understand energy transfer mechanisms in 2D-organic heterostructures.

Contribution

The paper introduces the first detailed characterization of hybrid excitons with mixed Frenkel-Wannier character at TMD/OSC interfaces using ultrafast momentum microscopy and many-body theory.

Findings

Hybrid excitons exhibit both Frenkel and Wannier characteristics.

Ultrafast resonant F"orster energy transfer facilitates hybrid exciton formation.

Insights into energy transfer mechanisms at 2D-organic interfaces are provided.

Abstract

Two-dimensional transition metal dichalcogenides (TMDs) and organic semiconductors (OSCs) have emerged as promising material platforms for next-generation optoelectronic devices. The combination of both is predicted to yield emergent properties while retaining the advantages of their individual components. In OSCs the optoelectronic response is typically dominated by localized Frenkel-type excitons, whereas TMDs host delocalized Wannier-type excitons. However, much less is known about the spatial and electronic characteristics of excitons at hybrid TMD/OSC interfaces, which ultimately determine the possible energy and charge transfer mechanisms across the 2D-organic interface. Here, we use ultrafast momentum microscopy and many-body perturbation theory to elucidate a hybrid exciton at an TMD/OSC interface that forms via the ultrafast resonant F\"orster energy transfer process. We show that this hybrid exciton has both Frenkel- and Wannier-type contributions: Concomitant intra- and interlayer electron-hole transitions within the OSC layer and across the TMD/OSC interface, respectively, give rise to an exciton wavefunction with mixed Frenkel-Wannier character. By combining theory and experiment, our work provides previously inaccessible insights into the nature of hybrid excitons at TMD/OSC interfaces. It thus paves the way to a fundamental understanding of charge and energy transfer processes across 2D-organic heterostructures.