Fundamental Charge Transfer Dynamics in 2D TMDCs for Use in Novel Heterostructures

Abstract

Efficient transfer of charge carriers and/or excitons between small organic molecules and two-dimensional (2D) semiconductor interfaces is being explored for applications in photovoltaics and quantum information processing.Interfaces of small molecules and 2D semiconductors such as graphene, nanocrystals, quantum dots and transition metal dichalcogenides (TMDCs) are capable of charge, energy, and spin singlet transfer. The long excited state lifetimes of spin triplet excitons makes triplet exciton transfer across such interfaces advantageous for exciton harvesting and photon upconversion. However, to date, triplet energy transfer between physisorbed small molecules and monolayer TMDCs has only been reported in a single study. To our knowledge, the process where photoexcitation of a TMDC/organic interface yields triplet excitons in the TMDC layer has not been reported. In quantum dot (QD) systems, direct covalent attachment of organic molecules to QD surfaces has shown to facilitate triplet energy transfer across the QD/molecule interface, but this covalent approach has not been widely applied to TMDC/molecule interfaces.Here we present a systematic study of covalently functionalized TMDC/molecule interfaces employing synthetically tailored thiolated acenes. We create tunable amounts of sulfur vacancies, which allows for subsequent covalent acene functionalization. We study the impact of covalent bonding on the charge transfer (CT) dynamics of TMDC/organic interfaces with energy level offsets suitable for charge and energy transfer (ET) as well as triplet acceptance and sensitization. We characterize the interfaces with a variety of steady-state and time-resolved spectroscopic techniques and initial results show success in selective isolation of CT vs ET pathways. Figure 1