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


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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Figure 1: Solar-to-hydrogen isoefficiency contour plot and bandgap versus lattice constant for various III–V alloys.
Figure 2: Structure of an IMM photocathode configured for water splitting with TEM cross-section of the active layers.
Figure 3: Structure of tandem devices and photoelectrochemical characterization.


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The authors thank W. Olavarria for operating the epitaxy system, M. Young for processing samples, A. Norman for the HAADF-STEM, and D. Friedman, J. Geisz and S. Ward for valuable discussions. J.L.Y. acknowledges support by a National Science Foundation Graduate Research Fellowship (Grant No. DGE1144083), H.D. by an EU Marie Curie Fellowship (IOF no. 300971), and all authors by the US Department of Energy (DOE), Office of Energy Efficiency & Renewable Energy, Fuel Cell Technologies Office under Contract No. DE-AC36-08GO28308 with the National Renewable Energy Laboratory.

Author information




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.

Corresponding author

Correspondence to Todd G. Deutsch.

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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.

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Supplementary Information

Supplementary Figures 1–9; Supplementary Table 1; Supplementary Note 1; Supplementary References (PDF 1330 kb)

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Young, J., Steiner, M., Döscher, H. et al. Direct solar-to-hydrogen conversion via inverted metamorphic multi-junction semiconductor architectures. Nat Energy 2, 17028 (2017).

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