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

Journal Article · 10 December 2019 · Nano Letters

DOI: https://doi.org/10.1021/acs.nanolett.9b04225 · OSTI ID:1633778

Yalamanchili, Sisir ^[1]; Verlage, Erik ^[1]; Cheng, Wen-Hui  ^[1]; Fountaine, Katherine T. ^[2]; Jahelka, Philip R. ^[1]; Kempler, Paul A. ^[1]; Saive, Rebecca ^[1]; Lewis, Nathan S.  ^[1]; Atwater, Harry A.  ^[1]

---

1. California Institute of Technology (CalTech), Pasadena, CA (United States)
2. NGNext, Redondo Beach, CA (United States)

We describe here 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 demonstrated 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

• Research Organization: California Institute of Technology (CalTech), Pasadena, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF)
• Grant/Contract Number: SC0004993; EEC-1041895
• OSTI ID: 1633778
• Journal Information: Nano Letters, Vol. 20, Issue 1; ISSN 1530-6984
• Publisher: American Chemical SocietyCopyright Statement
• Country of Publication: United States
• Language: English