Nanoscale semiconductor/catalyst interfaces in photoelectrochemistry

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Semiconductor structures (for example, films, wires, particles) used in photoelectrochemical devices are often decorated with nanoparticles that catalyse fuel-forming reactions, including water oxidation, hydrogen evolution or carbon-dioxide reduction. For high performance, the catalyst nanoparticles must form charge-carrier-selective contacts with the underlying light-absorbing semiconductor, facilitating either hole or electron transfer while inhibiting collection of the opposite carrier. Despite the key role played by such selective contacts in photoelectrochemical energy conversion and storage, the underlying nanoscale interfaces are poorly understood because direct measurement of their properties is challenging, especially under operating conditions. Using an n-Si/Ni photoanode model system and potential-sensing atomic force microscopy, we measure interfacial electron-transfer processes and map the photovoltage generated during photoelectrochemical oxygen evolution at nanoscopic semiconductor/catalyst interfaces. We discover interfaces where the selectivity of low-Schottky-barrier n-Si/Ni contacts for holes is enhanced via a nanoscale size-dependent pinch-off effect produced when surrounding high-barrier regions develop during device operation. These results thus demonstrate (1) the ability to make nanoscale operando measurements of contact properties under practical photoelectrochemical conditions and (2) a design principle to control the flow of electrons and holes across semiconductor/catalyst junctions that is broadly relevant to different photoelectrochemical devices.

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Fig. 1: Characteristics of photoanodes fabricated by electrodeposition of Ni nanoislands onto n-Si.
Fig. 2: Characterization of n-Si/Ni photoelectrodes obtained from 5-s deposition.
Fig. 3: Simulations showing how the pinch-off model explains performance enhancements with catalyst nanocontacts.
Fig. 4: Dual-working-electrode device measurement shows that high-barrier contacts are formed from oxidized NiOOH during operation.
Fig. 5: n-Si/Ni nanocontacts produce a pinched-off junction following activation.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Code availability

Code used for the pinch-off simulations can be downloaded as a Supplementary Information file.


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This work was funded by the Department of Energy, Basic Energy Sciences (award no. DE-SC0014279). F.A.L.L. acknowledges support from a NSF graduate research fellowship (no. 1309047). S.Z.O. acknowledges support from a research fellowship of the German Research Foundation (Deutsche Forschungsgemeinschaft, under project no. 408246589 (OE 710/1-1)). The atomic force microscope was purchased using funds provided by the NSF Major Research Instrumentation Program (grant no. DMR-1532225). We acknowledge use of shared instrumentation in the Center for Advanced Materials Characterization in Oregon and Rapid Materials Prototyping facilities, which are supported by grants from the M.J. Murdock Charitable Trust, the W.M. Keck Foundation, Oregon Nanoscience and Microtechnologies Institute and the National Science Foundation.

Author information

F.A.L.L. and S.W.B. conceived the experiments and led the project. F.A.L.L. conducted the analytical modelling/coding and the dual-working-electrode experiments. F.A.L.L. and M.R.N. performed the operando photoelectrochemical experiments. F.A.L.L., A.M.G., D.C.B. and J.L.F. prepared photoelectrodes and conducted the ex situ AFM experiments. S.Z.O. was responsible for cross-sectional scanning electron microscope (SEM) analysis and contributed significantly to analysis of diode properties from conductive AFM data. F.A.L.L. and S.W.B. wrote the manuscript with input from all authors.

Correspondence to Shannon W. Boettcher.

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Supplementary Information

Supplementary Table, Sections 1–11, Figs. 1–17 and Refs. 1–6

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