Light trapping in hematite-coated transparent particles for solar fuel generation

Abstract

due to its abundance and low-cost, is an attractive compound for photoelectrochemical splitting of water to produce hydrogen. However, one major obstacle preventing hematite from achieving the target efficiencies comprises its significantly smaller minority carrier transport distance relative to its optical absorption depth in the visible part of the optical spectrum. Here, we combine host-guest and Mie resonance concepts to achieve significant optical absorption in extremely thin layers of hematite. We propose and theoretically evaluate transparent particles coated with an extremely thin hematite shell as building blocks for hematite photoanodes. By full-field optical simulations we found out that maximal optical absorption is achieved when the particle supports two to three Mie resonance modes above the hematite optical absorption edge. Optical absorption efficiencies integrated over the air mass 1.5 global (AM1.5G) irradiance spectrum, hh abs i AM1.5 , reach more than 2 mA cm À2 within a 10 nm thick hematite shell of a particle with optimal dimensions and hh abs i AM1.5 comes close to 5 mA cm À2 in a 25 nm thick hematite shell. Furthermore, we evaluate the performance when the particles are part of an array or stacked atop each other. The concept introduced here could be useful for improving optical absorption in semiconductors with extremely short carrier transport distances.

Physical Modeling of Photoelectrochemical Hydrogen Production Devices

“…An important effect discovered with the particles is that placing them near each other, i.e. constructing an electrode, deteriorates their light absorption properties significantly 53 .…”

Micron-scale rod-like scattering particles for light trapping in nanostructured thin film solar cells

“…28 The refractive index of silica rods is 1.44, embedded in a mesoporous TiO 2 medium with complex effective index of 1.966+ik x . 23,24 In the modelling process, the total electromagnetic field, = + , is calculated which is the summation of the incident ( ) and scattered fields ( ). 34 In light trapping using scattering particles it is common to use the scattering cross-section (C sca ) of individual particles as a measure of the effectiveness of the light trapping process.…”

“…The sensitizers are dye molecules, quantum dots, or perovskite layers. [21][22][23][24] Some examples of these scattering particles are voids, 16,25 TiO 2 26 , and SiO 2 27 particles. This approach, however, is not appropriate for transparent solar cells applications.…”

“…Most of the sub-micron particles used so far have isotropic (nearly spherical) shape with dimensions chosen such that the particle supports optical resonance mode that enhance light scattering according to Mie theory. [21][22][23][24] Some examples of these scattering particles are voids, 16,25 TiO 2 , 26 and SiO 2 (ref. 27) particles.…”

Facile and low-cost synthesis of pure hematite (α-Fe2O3) nanoparticles from naturally occurring laterites and their superior adsorption capability towards acid-dyes

“…Similar to goethite, it is extremely stable and is oen the end form of transformations of other iron oxides. Hematite is an important pigment and a valuable ore. 21 On the other hand, nanoparticles of hematite are used in various advanced applications such as solar water oxidation 20,[22][23][24][25] and water purication.…”