The Energetics of p/n Photoelectrolysis Cells

L. Fornarini, A. J. Nozik, B. A. Parkinson

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The energetics of p/n photoelectrochemical cells, containing simultaneously illuminated p-type photocathodes and n-type photoanodes, have been investigated by using appropriate combinations of n-WSe2, n-MoSe2, n-WS2, n-TiO2, p-InP, p-GaP, and p-Si semiconductor electrodes. The open-circuit photovoltages (EOCV) of the p/n cells were measured as a function of the redox reactions in the cell and as function of light intensity. For many semiconductor electrode combinations, the sum of EOCV plus the standard cell voltage for the net cell reaction (ΔE°) was found to be constant for a given pair of n-and p-type electrodes at a given light intensity. This constancy was shown to be equivalent to the constancy of the sum of the band bending in the semiconductor depletion layers and the sum of the electrode overvoltages. These results are explained by movement of the semiconductor band edges with changes in the redox reactions that occur at the semiconductor electrode. If special care is taken to produce semiconductor electrodes that do not show surface charging effects, EOCV was found to be independent of the redox reaction. This is the expected behavior for pinned band edges. The dependence of EOCV on light intensity for p-InP/n-MoSe2 cells was either about 60 mV or about 130 mV per decade increase in light intensity. The latter value occurred when both the p-InP and n-MoSe2 band edges were pinned, while the former value occurred when only the p-InP band edge was pinned. These conditions for band-edge pinning depended upon light intensity and the nature of the electrolyte.

Original languageAmerican English
Pages (from-to)3238-3243
Number of pages6
JournalJournal of Physical Chemistry
Issue number15
StatePublished - 1984

NREL Publication Number

  • ACNR/JA-236-3823


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