An analysis of the optimal band gaps of light absorbers in integrated tandem photoelectrochemical water-splitting systems

Shu Hu, Chengxiang Xiang, Sophia Haussener, Alan D. Berger, Nathan S. Lewis

Research output: Contribution to journalArticlepeer-review

359 Citations (Scopus)

Abstract

The solar-to-hydrogen (STH) efficiency limits, along with the maximum efficiency values and the corresponding optimal band gap combinations, have been evaluated for various combinations of light absorbers arranged in a tandem configuration in realistic, operational water-splitting prototypes. To perform the evaluation, a current-voltage model was employed, with the light absorbers, electrocatalysts, solution electrolyte, and membranes coupled in series, and with the directions of optical absorption, carrier transport, electron transfer and ionic transport in parallel. The current density vs. voltage characteristics of the light absorbers were determined by detailed-balance calculations that accounted for the Shockley-Queisser limit on the photovoltage of each absorber. The maximum STH efficiency for an integrated photoelectrochemical system was found to be ∼31.1% at 1 Sun (=1 kW m-2, air mass 1.5), fundamentally limited by a matching photocurrent density of 25.3 mA cm-2produced by the light absorbers. Choices of electrocatalysts, as well as the fill factors of the light absorbers and the Ohmic resistance of the solution electrolyte also play key roles in determining the maximum STH efficiency and the corresponding optimal tandem band gap combination. Pairing 1.6-1.8 eV band gap semiconductors with Si in a tandem structure produces promising light absorbers for water splitting, with theoretical STH efficiency limits of >25%.

Original languageEnglish
Pages (from-to)2984-2993
Number of pages10
JournalEnergy and Environmental Science
Volume6
Issue number10
DOIs
Publication statusPublished - Oct 2013

ASJC Scopus subject areas

  • Environmental Chemistry
  • Renewable Energy, Sustainability and the Environment
  • Nuclear Energy and Engineering
  • Pollution

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