Design of Integrated III-Nitride/Non-III-Nitride Tandem Photovoltaic Devices

Nikholas G. Toledo, Daniel J. Friedman, Robert M. Farrell, Emmett E. Perl, Chieh Ting Lin, John E. Bowers, James S. Speck, Umesh K. Mishra

Research output: Contribution to journalArticlepeer-review

26 Scopus Citations


The integration of III-nitride and non-III-nitride materials for tandem solar cell applications can improve the efficiency of the photovoltaic device due to the added power contributed by the III-nitride top cell to that of high-efficiency multi-junction non-III-nitride solar cells if the device components are properly designed and optimized. The proposed tandem solar cell is comprised of a III-nitride top cell bonded to a non-III-nitride, series-constrained, multi-junction subcell. The top cell is electrically isolated, but optically coupled to the underlying subcell. The use of a III-nitride top cell is potentially beneficial when the top junction of a stand-alone non-III-nitride subcell generates more photocurrent than the limiting current of the non-III-nitride subcell. Light producing this excess current can either be redirected to the III-nitride top cell through high energy photon absorption, redirected to the lower junctions through layer thickness optimization, or a combination of both, resulting in improved total efficiency. When the non-III-nitride cell's top junction is the limiting junction, the minimum power conversion efficiency that the III-nitride top cell must contribute should compensate for the spectrum filtered from the multi-junction subcell for this design to be useful. As the III-nitride absorption edge wavelength, λ N, increases, the performance of the multi-junction subcell decreases due to spectral filtering. In the most common spectra of interest (AM1.5 G, AM1.5 D, and AM0), the technology to grow InGaN cells with λ N < 520 nm is found to be sufficient for III-nitride top cell applications. The external quantum efficiency performance, however, of state-of-the-art InGaN solar cells still needs to be improved. The effects of surface/interface reflections are also presented. The management of these reflection issues determines the feasibility of the integrated III-nitride/non-III-nitride design to improve overall cell efficiency.

Original languageAmerican English
Article number054503
Number of pages8
JournalJournal of Applied Physics
Issue number5
StatePublished - 1 Mar 2012

NREL Publication Number

  • NREL/JA-5200-55129


  • acoustic filters
  • band gap
  • converters
  • nitrides
  • photoconductivity
  • photovoltaics
  • quantum efficiency
  • solar cells
  • spectral methods
  • tectonophysics


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