Atomistic Simulations of Charge Separation at a Nanohybrid Interface: Relevance of Photoinduced Initial State Preparation

Charge separation kinetics at a nanohybrid interface are investigated in their dependence on ultrafast optical excitation. A prototypical organic/inorganic interface is considered. It is formed by a vertical stacking of 20 para-sexiphenyl molecules physisorbed on a ZnO nanocluster of 3783 atoms. A first principle parametrized Hamiltonian is employed, and the photoinduced subpicosecond evolution of Frenkel-excitons in the organic part is analyzed besides the formation of charge separated states across the interface. The interface absorption spectrum is calculated. Together, the data indicate that the charge separation is based on the direct excitation of the charge separated states but also on the migration of created Frenkel excitons to the interface with subsequent decay. Further, the photoinduced interface dynamics are compared with data resulting from direct set-ups of an initially excited state. Mostly such set-ups lead to substantially different charge separation processes.