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Multiple exciton generation in colloidal silicon nanocrystals.

Matthew C Beard1, Kelly P Knutsen, Pingrong Yu

  • 1National Renewable Energy Laboratory, Golden, Colorado 80401, USA. matt_ beard@nrel.gov

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Multiple exciton generation (MEG) in silicon nanocrystals (NCs) was observed for the first time. This breakthrough in indirect-gap semiconductors could significantly boost solar cell efficiency.

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Area of Science:

  • Materials Science
  • Nanotechnology
  • Photovoltaics

Background:

  • Multiple exciton generation (MEG) is a process where one photon creates multiple excitons, enhancing solar cell efficiency.
  • Silicon (Si) is the dominant material in the photovoltaic industry due to its abundance, low cost, and non-toxicity.

Purpose of the Study:

  • To report the first observation of MEG in colloidal silicon nanocrystals (NCs).
  • To investigate the MEG threshold and quantum yield in Si NCs.
  • To explore the potential of Si NCs for next-generation solar cells.

Main Methods:

  • Ultrafast transient absorption spectroscopy was used to measure MEG yields.
  • Colloidal Si NCs with a diameter of 9.5 nm were synthesized and characterized.

Main Results:

  • The threshold photon energy for MEG in Si NCs was determined to be 2.4 ± 0.1 times the band gap (Eg).
  • An exciton-production quantum yield of 2.6 ± 0.2 excitons per absorbed photon was achieved at 3.4Eg.
  • MEG was observed in relatively large Si NCs, indicating that confinement energy is not the sole factor for efficient MEG.

Conclusions:

  • This study demonstrates MEG in indirect-gap semiconductor NCs for the first time.
  • Silicon NCs show significant potential for improving solar energy conversion efficiency.
  • The findings are crucial for advancing silicon-based photovoltaic technologies.