We carry out ab initio nonadiabatic molecular dynamics (NAMD) simulations to study the fast relaxations of hot electrons in a CdSe quantum dot (QD). A novel global flux surface hopping (GFSH) approach is adopted. The investigated system forms the basis for QD-sensitized semiconductor solar cells and the presence of well-separated conduction electron states opens the possibility of energy selectivity for hot carriers. To elucidate the role of surface ligand in the process, we study the dynamics of CdSe QD passivated by a 1,6-hexanedithiol ligand. The intraband relaxation of the photoexcited electron from the 1Pe to 1Se state is accelerated due to the Auger-type relaxation. The ligand forms a hole trapping state, which competes with the Auger-type relaxation impeding the electron-hole energy exchange. The present study establishes the basic theoretical model describing the relaxation processes in both scenarios. The model is supported by computational studies of relaxation dynamics in model QD-ligand complexes. The obtained interplay between the competing phonon-assisted Auger and ligand-induced trapping mechanisms has given us a comprehensive picture of the complex photoinduced dynamic related to QDs, and shed lights to enhance the extraction efficiency of hot charge carriers for photovoltaic and photocatalytic applications.

Auger relaxation of hot electrons in CdSe quantum dots using GFSH

249th National Meeting (2015)

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