High Efficiency Carrier Multiplication in PbSe Nanocrystals: Implications for Solar Energy Conversion

We demonstrate for the first time that impact ionization occurs with very high efficiency in semiconductor nanocrystals

R. D. Schaller

2004

Scholarcy highlights

  • We demonstrate for the first time that impact ionization occurs with very high efficiency in semiconductor nanocrystals
  • Several methods have been offered to increase the power conversion efficiency of solar cells including the development of tandem cells, impurity band and intermediate band devices, hot electron extraction, and carrier multiplication
  • Carrier multiplication, which was first observed in bulk semiconductors in the 1950s, would provide increased power conversion efficiency in the form of increased solar cell photocurrent
  • As was first proposed by Nozik, nanosize semiconductor crystals might provide a regime where carrier multiplication could be greatly enhanced through impact ionization
  • By directly monitoring exciton conversion to biexcitons in the time domain, we show that II in PbSe NCs is highly efficient, extremely fast, and occurs in a wavelength range that has potential to provide significantly increased solar cell power conversion efficiency
  • Schaller et al power conversion efficiency at ηii=100% in comparison to the efficiency of a cell without II
  • For a photovoltaic cell based on PbSe NCs of a single size, we can estimate the NC Eg required to achieve maximum power conversion efficiency in the presence of II under concentrated solar illumination conditions, assuming the internal quantum efficiency of the device to be 1
  • A 37% increase in relative power conversion efficiency can be achieved via minimization of the II threshold to 2Eg, which should be realizable in NCs of materials that have significantly different carrier effective masses

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