Insights into the Charge Separation Dynamics in Photoexcited Molecular Junctions

The transient dynamics of charge transfer induced by a femtosecond laser pulse at the donor-acceptor interface of molecular junctions is investigated by means of quantum transport calculations within the nonequilibrium Green's function formalism. Simulations are implemented from the wave function technique extended to include Coulombic interaction within the Hartree-Fock approximation. Exciton and charge-transfer states competitively impact the molecular hybridization and thus provoke a charge localization visible in the time-resolved density of states, which modifies the time-resolved photocurrent spectra. The dynamic nature of the exciton and charge-transfer state formation leads to the definition of a dynamic driving energy. Our findings suggest the need to reconsider the role of built- in molecular orbital offset for design and experimentation. Insights provided in this work will contribute to designing ultrafast molecular optoelectronics and improving ultrafast spectroscopy techniques.