Exciton Dissociation, Charge Transfer, and Exciton Trapping at the MoS2/Organic Semiconductor Interface

Hybrid inorganic-organic semiconducting devicesconsistingof monolayer transition metal dichalcogenides (TMDs) represent a newfrontier in advanced optoelectronics due to their high radiative efficienciesand capacity to form flexible p-n junctions with inherent devicetunability. However, understanding how excitons and charges behaveat the interface between TMDs and organic systems, a key requirementto advance the field, remains underexplored. Herein, a heterostructureconsisting of a highly conjugated organic system, 9-(2-naphthyl)-10-[4-(1-naphthyl)-phenyl]-anthracene(ANNP), and monolayer molybdenum disulfide (MoS2) on quartzis elucidated via transient absorption and photoluminescence spectroscopies.Upon direct excitation of MoS2 at 532 nm, hole transferto ANNP of similar to 5 ps and a charge separation time constant of similar to 2.4ns are observed. When the sample is excited at 400 nm (where bothANNP and MoS2 absorb), a self-trapped exciton within ANNPis formed. The emission of the self-trapped exciton is long-livedcompared to the exciton lifetime of ANNP, decaying within 20 ns. Thetrapping of the ANNP exciton is caused by structural deformities ofthe ANNP crystal lattice when grown on MoS2, which areremoved by annealing the film. These observations highlight how excitondissociation and charge transfer dominate at the interface of ANNPand MoS2 whereas the exciton dynamics within ANNP are proneto the formation of trap states brought about by crystal defects withinthe film. These insights will aid in future developments of TMD-containingoptoelectronics.