Subpicosecond Charge Separation Time Scale at Graphene Quantum Dot Surface
Krishna Mishra, Ayendrila Das, Subhadip Ghosh
Abstract
Fast exciton–exciton annihilation occurring at a few 10s ps time scale possesses a potential hurdle to the successful utilization of a multiple exciton generation (MEG) process. MEG produces over 100% quantum efficiency of exciton generation and thereby a dramatic improvement in device performance. Successful implementation of MEG would require a faster charge separation than the exciton annihilation time. In this work we showed < 1 ps photoinduced electron transfer (PET) time scale at graphene quantum dot (GQD)/N,N-dimethylaniline (DMA) interface that would probably allow electron–hole separation much before it annihilates. Modern experimental techniques, including ensemble-based femtosecond fluorescence upconversion and single molecule sensitive fluorescence correlation spectroscopy (FCS), are employed for an in-depth study of PET kinetics. Former technique asserts the ultrafast nature of interfacial PET kinetics, while FCS reveals weak molecular interactions resulting in short-lived (∼4–6 μs) GQD-DMA complex formation in water. A few microseconds binding time allowed us to measure accurately the much faster (<1 ps) intrinsic PET time scale in GQD-DMA complex before it dissociates.