Article

Direct solar-to-hydrogen conversion via inverted metamorphic multi-junction semiconductor architectures

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Abstract

Solar water splitting via multi-junction semiconductor photoelectrochemical cells provides direct conversion of solar energy to stored chemical energy as hydrogen bonds. Economical hydrogen production demands high conversion efficiency to reduce balance-of-systems costs. For sufficient photovoltage, water-splitting efficiency is proportional to the device photocurrent, which can be tuned by judicious selection and integration of optimal semiconductor bandgaps. Here, we demonstrate highly efficient, immersed water-splitting electrodes enabled by inverted metamorphic epitaxy and a transparent graded buffer that allows the bandgap of each junction to be independently varied. Voltage losses at the electrolyte interface are reduced by 0.55 V over traditional, uniformly p-doped photocathodes by using a buried p–n junction. Advanced on-sun benchmarking, spectrally corrected and validated with incident photon-to-current efficiency, yields over 16% solar-to-hydrogen efficiency with GaInP/GaInAs tandem absorbers, representing a 60% improvement over the classical, high-efficiency tandem III–V device.

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Author information

Affiliations

  1. National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA

    • James L. Young
    • , Myles A. Steiner
    • , Henning Döscher
    • , Ryan M. France
    • , John A. Turner
    •  & Todd G. Deutsch
  2. Philipps-Universität Marburg, Hans-Meerwein-Strasse 6, MZG 02D28, 35032 Marburg, Germany

    • Henning Döscher

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Contributions

J.L.Y. performed the characterizations, developed the benchmarking procedures, and wrote the manuscript. T.G.D., J.A.T., J.L.Y. and H.D. developed the concept of IMM water splitting while T.G.D., J.A.T., J.L.Y., H.D. and M.A.S. participated in design of experiments and interpretation of results. H.D. modelled PEC tandem device efficiencies and characterized some initial proof-of-principle devices. M.A.S. designed the semiconductor growths and performed the semiconductor photolithography and isolation. R.M.F. developed the transparent graded buffers and metamorphic subcells.

Competing interests

T.G.D., J.A.T., J.L.Y., H.D., M.A.S. and R.M.F. have a provisional patent (No. US 2016/0281247/A1) on file with the US Patent and Trademark Office that is based on this work.

Corresponding author

Correspondence to Todd G. Deutsch.

Supplementary information

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    Supplementary Information

    Supplementary Figures 1–9; Supplementary Table 1; Supplementary Note 1; Supplementary References