Ab initio theory of impact ionization applied to silicon nanocrystals

ORAL

Abstract

Achieving multi exciton generation (MEG) in semiconducting nanocrystals may lead to overcome the well-known Shockley-Queisser limit when building semiconductor-based solar cells. A thourough, theoretical understanding of the experiments that reported MEG in e.g. Si and PbSe nanocrystals, is still missing and could significantly contribute to clarify the several controversial results in the field. Several theoretical and numerical studies have addressed the origin of the MEG formation, mostly supporting an impact ionization mechanism. However, impact ionization rates have only been evaluated for model nanocrystals by using empirical pseudopotentials fitted to bulk properties, and model dielectric functions to describe the screened Coulomb interaction. We present an ab-initio scheme based on Density Functional Theory in a plane-wave pseudopotential implementation that includes static screening within the random-phase approximation. We will discuss how impact ionization rates are affected by the shape and surface structure of few nm Si nanocrystals.

–

Authors

  • Marton Voros

    Budapest University of Technology and Economics

  • Adam Gali

    Hungarian Academy of Sciences, Research Institute for Solid State Physics and Optics, Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences

  • Dario Rocca

    UC Davis, University of California-Davis, Department of Chemistry, University of California, Davis

  • Gergely Zimanyi

    UC Davis

  • Giulia Galli

    University of California, Davis, Department of Chemistry and Department of Physics, University of California at Davis, Davis, California, USA, Department of Chemistry \& Department of Physics, Unversity of California, Davis, Department of Chemistry and Department of Physics, UC Davis, UC Davis, University of California-Davis, Department of Chemistry and Department of Physics, University of California, Davis, Univeristy of California, Davis, University of California Davis, Davis, CA95616, University of California, Davis, USA