Highly Efficient Semiconductor-Based Metasurface for Photoelectrochemical Water Splitting: Broadband Light Perfect Absorption with Dimensions Smaller than the Diffusion Length

Abstract

In this paper, we demonstrate a highly efficient light trapping design that is made of a metal-oxide-semiconductor-semiconductor (nanograting/nanopatch) (MOSS g/p) four-layer design to absorb light in a broad wavelength regime in dimensions smaller than the hole diffusion length of the active layer. For this aim, we first adopt a modeling approach based on the transfer matrix method (TMM) to find out the absorption bandwidth (BW) limits of a simple hematite (α-Fe 2 O 3)-based metal-oxide-semiconductor (MOS) cavity design. Our modeling findings show that this design architecture can provide near-perfect absorption in shorter wavelengths. To extend the absorption toward longer wavelengths, a nanostructured semiconductor is placed on top of this MOS design. This nanostructure supports the Mie resonance and adds a new resonance in longer wavelengths without disrupting the lower wavelength absorption capability of MOS cavity. By this way, a polarization-insensitive absorption above 0.8 can be acquired up to λ=565 nm. Moreover, to have a better qualitative comparison, the water-splitting photocurrent of this design has been estimated. Our calculations show that a photocurrent as high as 10.6 mA cm −2 can be achieved with this design that is quite close to the theoretical limit of 12.5 mA cm −2 for hematite-based water-splitting photoanode. This paper proposes a design approach in which the superposition of cavity modes and Mie resonances can lead to a broadband, polarization-insensitive, and omnidirectional near-perfect light absorption in dimensions smaller than the carrier's diffusion length. This can be considered as a winning strategy to design highly efficient and ultrathin optoelectronic designs in a variety of applications including photoelectrochemical water splitting and photovoltaics.

Optical Resonator Enhanced Photovoltaics and Photocatalysis: Fundamental and Recent Progress

“…Furthermore, Ghobadi et al designed a semiconductor based device with a nanopatch top layer, which leads to high photon absorption in covering the broad spectral region. [211] Taking advantage of broadband, large light absorption, polarization insensitivity, and good angular response, the measured photocurrent was close to the theoretical limit. Very recently, Li.…”

Metasurface Photoelectrodes for Enhanced Solar Fuel Generation

“…Broadband visible-near-infrared (NIR) light absorption is a key requirement for efficient solar energy harvesting by photocatalysts. The excitation of Mie-resonances in nanostructured photocatalysts is a promising route for trapping light in high aspect-ratio nanoparticles and provides three major advantages: [1][2][3][4][5][6] First, Mie-resonances facilitate spectral enhancement of light absorption beyond the bulk property of the material. Second, in a sub-micrometer-sized particle, most absorption caused by the in-phase coupling of dipolar modes of closely spaced resonators and can be spectrally tuned by the array periodicity.…”

Effect of Sn valence state in the in situ growth of FeOOH precursor on the performance of the α-Fe2O3 photoanode

“…[16][17][18] Theoretically, a-Fe 2 O 3 is estimated to exhibit a photocurrent as high as 12.5 mA cm À2 and nearly 15.8% solar-to-hydrogen efficiency (STH). 19,20 Nevertheless, practical photocurrent for a-Fe 2 O 3 photoanodes is found to be much lower than the theoretical value. To date, the largest photocurrent was reported to be only 6 mA cm À2 , which was based on hydrogen treatment of the a-Fe 2 O 3 nanorod arrays to improve their electrical conductivity, passivation of the surface with an ultra-thin TiO 2 film and further deposition of Co-Pi as a cocatalyst.…”