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Published January 8, 2020 | Supplemental Material
Journal Article Open

High Broadband Light Transmission for Solar Fuels Production Using Dielectric Optical Waveguides in TiO₂ Nanocone Arrays


We describe the fabrication and use of arrays of TiO₂ nanocones to yield high optical transmission into semiconductor photoelectrodes covered with high surface loadings of light-absorbing electrocatalysts. Covering over 50% of the surface of a light absorber with an array of high-refractive-index TiO₂ nanocones imparted antireflective behavior (< 5% reflectance) to the surface and allowed > 85% transmission of broadband light to the underlying Si, even when thick metal contacts or opaque catalyst coatings were deposited on areas of the light-facing surface that were not directly beneath a nanocone. Three-dimensional full-field electromagnetic simulations for the 400 – 1100 nm spectral range showed that incident broadband illumination couples to multiple waveguide modes in the TiO₂ nanocones, reducing interactions of the light with the metal layer. A proof-of-concept experimental demonstration of light-driven water oxidation was performed using a p⁺n-Si photoanode decorated with an array of TiO₂ nanocones additionally having a Ni catalyst layer electrodeposited onto the areas of the p⁺n-Si surface left uncovered by the TiO₂ nanocones. This photoanode produced a light-limited photocurrent density of ~ 28 mA cm⁻² under 100 mW cm⁻² of simulated Air Mass 1.5 illumination, equivalent to the photocurrent density expected for a bare planar Si surface even though 54% of the front surface of the Si was covered by an ~ 70 nm thick Ni metal layer.

Additional Information

© 2019 American Chemical Society. Received: October 12, 2019; Revised: November 29, 2019; Published: December 10, 2019. The fabrication and assessment of photoanodes for the oxygen-evolution reaction was supported through the Office of Science of the U. S. Department of Energy under Award No. DE-SC0004993 for the Joint Center for Artificial Photosynthesis and used facilities of the Kavli Nanoscience Institute at Caltech, a DOE Energy Innovation Hub; the development of simulations was supported by the National Science Foundation under award No. EEC-1041895. Author Contributions: S.Y., E.V., and W.H.C. contributed equally. The authors declare no competing financial interest.

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