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

Abstract

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 lightabsorbing 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.

Hydrogen from Sunlight and Water: A Side-by-Side Comparison between Photoelectrochemical and Solar Thermochemical Water-Splitting

“…Notably, Earth-abundant, mixed-metal oxides, such as NiFeO x , are often good candidates for OER, and mixed metals, such as NiMo, are often good candidates for HER in alkaline conditions. ,− However, discovery of efficient and stable OER catalysts with Earth-abundant materials in acidic conditions is not yet in hand . One unique requirement for optimal catalysts for PEC water-splitting is the optical transparency of the catalyst to facilitate efficient light collection; various strategies that optimize the light path at the electrolyte/catalyst/semiconductor interfaces can further boost the device efficiency and expand the materials selections. − In addition, little is known about dynamic operations (diurnal cycles and bad weather days) and their impact on catalyst materials, which would be necessary to understand for real-world operation. For PEC devices, recent demonstrations of unassisted PEC water-splitting with various configurations exist, with STH conversion efficiencies that exceed 10% and device stability in the range of tens to hundreds of hours. − However, significant challenges remain in bringing the current PEC scale (typically <0.01 g/day) to the bench scale (0.1 kg/day) or subscale (2 kg/day). , In addition, standardization of device architectures and benchmarking conditions are important to meaningfully compare results and performances across different PEC materials from the research community .…”

Novel Method of Measuring the Thickness of Nanoscale Films Using Energy Dispersive X‐Ray Spectroscopy Line Scan Profiles

“…In most thinfilm application cases, the thickness of thin films (along with their crystallography and chemical composition) greatly affects the performance of the devices and the final products. [1][2][3] There are multiple examples in which the performance of the materials containing naturally formed thin films [4,5] (as well as the performance of the devices utilizing artificially deposited thin films [6][7][8][9] ) is strongly related to their thickness. than crystalline specimen.…”

The annual energy yield of mono- and bifacial silicon heterojunction solar modules with high-index dielectric nanodisk arrays as anti-reflective and light trapping structures

“…In response to that need, various nanophotonic concepts 6 applicable to c-Si-based solar cell stacks were proposed to enhance light harvesting through improved light in-coupling on the front surface. Examples of possible solutions include plasmonic structures, [7][8][9] period-ically arranged silicon 10,11 and dielectric [12][13][14] nanoscatterers, and biomimetic structures. 15 Moreover, double-sided AR and light trapping (LT) nanostructure gratings introduced at the front and rear sides of the solar cells were also suggested.…”