Unravelling the Surface-State Assisted Ultrafast Charge Transfer Dynamics of Graphene Quantum Dot-Based Nanohybrids via Transient Absorption Spectroscopy
Deepa Sebastian, Athira Pallikkara, Himanshu Bhatt, Hirendra N. Ghosh, Kala Ramakrishnan
Abstract
Graphene quantum dots-based nanohybrids (GQD NHs) are considered to be a promising candidate for optoelectronic devices due to their tunable light absorption and pronounced carrier transfer properties. The mechanism of GQD exciton dynamics remains an open problem despite the substantial studies conducted so far. The carrier annihilation process occurring at a femtosecond time scale becomes the greatest hurdle in the path of GQD quantum efficiency. In this quest, we investigated a surface state-assisted photoinduced charge (electron/hole) transfer (PCT) in GQD-(p-methoxy aniline (POMe)/p-nitroaniline (PNO)) nanohybrids by using mainly ultrafast transient absorption spectroscopic technique. The ultrafast PCT time was found to be ∼0.3 ps (ps) and ∼0.4 ps for GQD/PNO and GQD/POMe NHs, respectively. The fastest kinetics observed for GQD/POMe among these systems reveals a more efficient PCT interaction in the GQD/POMe interface than that of GQD/PNO. The higher PCT rate constant (KPCT) and high negative Gibbs free energy change (ΔG) values observed for GQD/POMe over GQD/PNO further validates the aforementioned results. Cyclic voltammetry along with theoretical studies reveal the thermodynamic viability of PCT in GQD NHs. Outcomes of this study fortify the comprehension of surface state-influenced PCT kinetics of GQD NHs and thus enlarge its optoelectronic applications.