Assessment of GaPSb/Si tandem material association properties for photoelectrochemical cells

Abstract

Here, the structural, electronic and optical properties of the GaP 1-x Sb x /Si tandem materials association are determined in view of its use for solar water splitting applications. The GaPSb crystalline layer is grown on Si by Molecular Beam Epitaxy with different Sb contents. The bandgap value and bandgap type of GaPSb alloy are determined on the whole Sb range, by combining experimental absorption measurements with tight binding (TB) theoretical calculations. The indirect (X-band) to direct (Γ-band) cross-over is found to occur at 30% Sb content. Especially, at a Sb content of 32%, the GaP 1-x Sb x alloy reaches the desired 1.7eV direct bandgap, enabling efficient sunlight absorption, that can be ideally combined with the Si 1.1 eV bandgap. Moreover, the band alignment of GaP 1-x Sb x alloys and Si with respect to water redox potential levels has been analyzed, which shows the GaPSb/Si association is an interesting combination both for the hydrogen evolution and oxygen evolution reactions. These results open new routes for the development of III-V/Si low-cost high-efficiency photoelectrochemical cells.

Photoelectrode/electrolyte interfacial band lineup engineering with alloyed III–V thin films grown on Si substrates

“…4, following the procedure already used in previous works. 12,25,32 Note that in the semiconductor research community, the CB edge energy is usually referred versus a vacuum level (and defined as the electron affinity). In order to compare energy versus RHE and versus vacuum, we consider that the chemical potential for electrons under the RHE is shifted by À4.48 eV on the vacuum scale.…”

“…[21][22][23][24] Following this strategy, band gap engineering was proposed theoretically to address the issue of band alignments between the semiconducting photoelectrodes and redox levels of the electrolyte, but without a clear experimental proof of the concept in electrochemistry. 25 In this work, we assess experimentally the opportunities offered by III-V alloys to tune at will the band lineups between semiconductor band energies and electrolyte water redox levels. For this purpose, we study the photoelectrochemical performance of photoelectrodes, made from GaP 1Àx As x alloys epitaxially grown on a cost-effective Si substrate.…”

“…21–24 Following this strategy, band gap engineering was proposed theoretically to address the issue of band alignments between the semiconducting photoelectrodes and redox levels of the electrolyte, but without a clear experimental proof of the concept in electrochemistry. 25…”