Solar hydrogen production using epitaxial SrTiO₃ on a GaAs photovoltaic

Abstract

We demonstrate an oxide-stabilized III-V photoelectrode architecture for solar fuel production from water in neutral pH. For this tunable architecture we demonstrate 100% Faradaic efficiency for hydrogen evolution, and incident photon-to-current efficiencies (IPCE) exceeding 50%. High IPCE for hydrogen evolution is a consequence of the low-loss interface achieved via epitaxial growth of a thin oxide on a GaAs solar cell. Developing optimal energetic alignment across the interfaces of the photoelectrode using well-established III-V technology is key to obtaining high performance. This advance constitutes a critical milestone towards efficient, unassisted fuel production from solar energy.

Epitaxial Oxides on Semiconductors: From Fundamentals to New Devices

“…For example, coupling of dielectric or ferroelectric polarization to a semiconductor typically requires a type‐I (straddling) arrangement, in which the conduction (valence) band of the oxide is above (below) the conduction (valence) band of the semiconductor, allowing the oxide to couple as a capacitor. Conversely, for photoelectrocatalysis schemes, a type‐II arrangement is desirable . Though epitaxial STO is an excellent platform for the subsequent growth of multifunctional oxides on semiconductors, the small (or even negative) conduction band offsets of STO on Si, Ge, and GaAs limits its use as an insulator …”

“…STO/np‐GaAs based PEC, e) band structure under illumination, f) high‐resolution TEM image of the interface (scale bar is 2 nm), inset showing a post‐growth RHEED pattern. Reproduced under the terms and conditions of the Creative Commons Attribution 3.0 Unported License . Copyright 20.17, The Authors, published by the Royal Society of Chemistry.…”

“…Following this study, Kornblum et al, explored the use of a direct bandgap GaAs pn‐junction solar cell in place of Si . In principle, the direct bandgap of GaAs, and the use of a pn‐junction enables more efficient absorption and generation of electron‐hole pairs.…”

“…Their heterojunctions were comprised of a 16 nm thick layer of epitaxial STO grown on a GaAs pn‐junction (Figure f), in which the n‐type side of the GaAs interfaced with the STO. With the conduction band of the GaAs situated above the conduction band of the STO, the heterojunction acts as a photocathode: photo‐generated electrons from the GaAs can be transported to the STO surface for reaction (Figure e). Faradaic efficiencies of 100% for hydrogen evolution were demonstrated, as well as incident photon‐to‐current efficiencies that exceeded 50%.…”

Understanding Surface Modulation to Improve the Photo/Electrocatalysts for Water Oxidation/Reduction

“…When the various thicknesses (2-25 nm) of LaFeO 3 are deposited on the Nb-doped SrTiO 3 , the films show a thickness-dependent charge transfer conductivity, and thus, a change in the open circuit potential. This is because the band bending of the valence-band in LaFeO 3 at the solid-solid interface generates sensitivity to the thickness of the materials (Figure 4a) [90][91][92]. Thus, in an absorber-metal oxide device structure, the thickness of the metal oxide layer, which functions as an insulator, could control the barrier height and further improve the photovoltage [91,93,94].…”