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Modeling integrated photovoltaic–electrochemical devices using steady-state equivalent circuits

  1. Tonio Buonassisia,2
  1. Departments of aMechanical Engineering and
  2. bChemistry, Massachusetts Institute of Technology, Cambridge, MA 02139

  1. Contributed by Daniel G. Nocera, January 25, 2013 (sent for review December 1, 2012)

Significance

This article extends the construction of direct solar-to-fuels devices, such as the artificial leaf based on crystalline silicon. Because a single Si junction has insufficient potential to drive water splitting, it cannot be used for direct solar-to-fuels conversion. This paper performs an equivalent circuit analysis for multiple series-connected devices. The predictive utility of the model is demonstrated in the case of water oxidation at the surface of a Si solar cell, using a cobalt–borate oxygen evolving catalyst. Considering recent cost reductions of Si solar cells, this paper offers a path to the construction of low cost solar-to-fuels devices.

Abstract

We describe a framework for efficiently coupling the power output of a series-connected string of single-band-gap solar cells to an electrochemical process that produces storable fuels. We identify the fundamental efficiency limitations that arise from using solar cells with a single band gap, an arrangement that describes the use of currently economic solar cell technologies such as Si or CdTe. Steady-state equivalent circuit analysis permits modeling of practical systems. For the water-splitting reaction, modeling defines parameters that enable a solar-to-fuels efficiency exceeding 18% using laboratory GaAs cells and 16% using all earth-abundant components, including commercial Si solar cells and Co- or Ni-based oxygen evolving catalysts. Circuit analysis also provides a predictive tool: given the performance of the separate photovoltaic and electrochemical systems, the behavior of the coupled photovoltaic–electrochemical system can be anticipated. This predictive utility is demonstrated in the case of water oxidation at the surface of a Si solar cell, using a Co–borate catalyst.

Footnotes

  • ↵1Present address: Physical Sciences Division, IBM T. J. Watson Research Center, Yorktown Heights, NY 10598.

  • ↵2To whom correspondence may be addressed. E-mail: nocera{at}mit.edu, mwinkler{at}post.harvard.edu, or buonassisi{at}mit.edu.

  • Author contributions: M.T.W., C.R.C., D.G.N., and T.B. designed research; M.T.W. and C.R.C. performed research; M.T.W., C.R.C., and T.B. analyzed data; and M.T.W., D.G.N., and T.B. wrote the paper.

  • The authors declare no conflict of interest.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1301532110/-/DCSupplemental.

Freely available online through the PNAS open access option.

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