Anomalous photoluminescence quenching in DIP/MoS2 van der Waals heterostructure: Strong charge transfer and a modified interface

Due to the fascinating optoelectronic properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) and the flexible nature, vast library, and easy fabrication process of organic molecules, the combination of 2D TMD materials and organic molecules have been gaining enormous attention in recent years. The organic semiconductors can enhance the optoelectronic and improved transport properties by interfacing with atomically thin TMDs through vdW interaction. Here, we investigate the photoluminescence (PL) properties of type-II heterostructure made of monolayer molybdenum disulfide (ML MoS2) and a non-planar Diindenoperylene (DIP) molecules. A drastic quenching of PL intensity nearly 300% is observed with slightly redshift in DIP/MoS2 as compared to the PL of isolated MoS2. The observed quenching behavior in DIP/MoS2 heterostructure can be explained by the appeared 'trap - like' states in density of states (DOS), and suppression of exciton to trion ratio due to electron transfer from the lowest unoccupied molecular orbital (LUMO) level of DIP to the conduction band minima (CBM) of MoS2. Furthermore, the redshift in the PL of heterostructure could be due to weak coupling strength which is similar to 8 times smaller than that of the energy of A-exciton resonance of individual layers and dielectric screening effect induced by the non-planar DIP based organic layer. The expected strong interaction between the DIP molecule and MoS2 layer due to the permanent dipole moments (significant molecular quadruple moment 8.25D) of DIP molecules is another reason, which may slightly reduce the bandgap and results in red-shift of PL. We observed Raman (A(1g) phonon mode) is blue-shifted, which is supposed to stiffening due to the non-planar DIP molecule onto ML MoS2. The strong PL quenching behavior of DIP/MoS2 heterostructure can be a potential candidate for tailoring the optoelectronic properties of TMDs that may demonstrate for light-harvesting and can serve as the next generation TMD/organic-based photovoltaic applications.