highly efficient semiconductor-based metasurface for photoelectrochemical water splitting: broadband light perfect absorption with dimensions smaller than the diffusion length

In this paper, we demonstrate a highly efficient light trapping design that is made of a metal-oxide-semiconductor-semiconductor (nanograting/nanopatch) (mossg/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-fe2o3)-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.