Emergent Excitons in Two-Dimensional Organic-Inorganic Van der Waals Heterostructures

The ability to synthesize new classes of chemically-diverse two-dimensional materials attractive for optoelectronic applications has driven the development of new theory, computational methods, and intuition for predicting the nature of their excitons and how they may be tuned. Here, we describe the recent synthesis and measurements of an emerging class of van der Waals heterostructures, namely a bilayer consisting of atomically-thin monolayers of non-covalently bonded molecular monomers interfaced with a transition metal dichalcogenide (TMD) monolayer. Specifically, we consider different recently-synthesized monolayers of perylene-derivative monomers, whose relative orientation can be tuned via choice of functional group, on MoSe₂ and WS₂ monolayers. We use state-of-the-art first-principles calculations – based on density functional theory and the ab initio GW-Bethe-Salpeter equation approach – to reveal the nature of the 2D molecular monolayer-TMD interface, their excitons, and their polarization-dependent optical response. We will describe how their excitonic properties are influenced by lattice structure, dielectric screening, and carrier concentration, and compare the predicted spectral response to photoluminescence and device measurements. General implications for similar systems are also discussed. This work is supported in part by ASOFR-MURI and DOE-BES. Computational resources provided by NERSC.