High-Pressure Core Structures of Si Nanoparticles for Solar Energy Conversion

S. Wippermann, M. Vörös, D. Rocca, A. Gali, G. Zimanyi, and G. Galli

Phys. Rev. Lett. 110, 046804 – Published 24 January 2013

Abstract

We present density functional and many body perturbation theory calculations of the electronic, optical, and impact ionization properties of Si nanoparticles (NPs) with core structures based on high-pressure bulk Si phases. Si particles with a BC8 core structure exhibit significantly lower optical gaps and multiple exciton generation (MEG) thresholds, and an order of magnitude higher MEG rate than diamondlike ones of the same size. Several mechanisms are discussed to further reduce the gap, including surface reconstruction and chemistry, excitonic effects, and embedding pressure. Experiments reported the formation of BC8 NPs embedded in amorphous Si and in amorphous regions of femtosecond-laser doped “black silicon.” For all these reasons, BC8 nanoparticles may be promising candidates for MEG-based solar energy conversion.

Received 1 August 2012

DOI:https://doi.org/10.1103/PhysRevLett.110.046804

Authors & Affiliations

S. Wippermann^1,2, M. Vörös³, D. Rocca¹, A. Gali^3,4, G. Zimanyi², and G. Galli^1,2

¹Department of Chemistry, University of California, Davis, California 95616, USA
²Department of Physics, University of California, Davis, California 95616, USA
³Department of Atomic Physics, Budapest University of Technology and Economics, Budafoki út 8, H-1111 Budapest, Hungary
⁴Institute for Solid State Physics and Optics, Wigner Research Center for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary