Band gap-voltage offset and energy production in next-generation multijunction solar cells

R. R. King, D. Bhusari, A. Boca, D. Larrabee, X. Q. Liu, W. Hong, C. M. Fetzer, D. C. Law, N. H. Karam

Research output: Contribution to journalArticlepeer-review

219 Scopus citations


The potential for new 4-, 5-, and 6-junction solar cell architectures to reach 50% efficiency is highly leveraging for the economics of concentrator photovoltaic (CPV) systems.The theoretical performance of such next-generation cells, and experimental results for 3- and 4-junction CPV cells, are examined here to evaluate their impact for real-world solar electricity generation. Semiconductor device physics equations are formulated in terms of the band gap-voltage offset Woc Eg/q) - Voc, to give a clearer physical understanding and more general analysis of the multiple subcell band gaps in multijunction cells. Band gap-voltage offset is shown experimentally to be largely independent of band gap Eg for a wide range of metamorphic and lattice-matched semiconductors from 0.67 to 2.1 eV. Its theoretical Eg dependence is calculated from that of the radiative recombination coefficient, and at a more fundamental level using the Shockley-Queisser detailed balance model, bearing out experimental observations. Energy production of 4-, 5-, and 6-junction CPV cells, calculated for changing air mass and spectrum over the course of the day, is found to be significantly greater than for conventional 3-junction cells. The spectral sensitivity of these next-generation cell designs is fairly low, and is outweighed by their higher efficiency. Lattice-matched GaInP/GaInAs/Ge cells have reached an independently confirmed efficiency of 41.6%, the highest efficiency yet demonstrated for any type of solar cell. Light I-V measurements of this record 41.6% cell, of next-generation upright metamorphic 3-junction cells with 40% target production efficiency, and of experimental 4-junction CPV cells are presented.

Original languageEnglish (US)
Pages (from-to)797-812
Number of pages16
JournalProgress in Photovoltaics: Research and Applications
Issue number7
StatePublished - Nov 1 2011
Externally publishedYes


  • III-V
  • band gap-voltage offset
  • concentrator
  • detailed balance
  • energy production
  • high-efficiency
  • multijunction
  • radiative recombination

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Condensed Matter Physics
  • Electrical and Electronic Engineering


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