Controllable Distribution of Oxygen Vacancies in Grain Boundaries of p‐Si/TiO₂ Heterojunction Photocathodes for Solar Water Splitting

Abstract

Silicon is a promising photocathode material in photoelectrochemical water splitting for hydrogen production, but it is primarily limited by photocorrosion in aqueous electrolytes. As an extensively used protective material, crystalline TiO2 could protect Si photoelectrode against corrosion. However, a large number of grain boundaries (GBs) in polycrystalline TiO2 would induce excessive recombination centers, impeding the carrier transport. This paper describes the introduction of oxygen vacancies (Ovac) with controllable spatial distribution for GBs to promote carrier transport. Two kinds of Ovac distribution, Ovac along GBs and Ovac inside grains, are compared, where the latter one is demonstrated to facilitate carrier transport owing to the formation of tunneling paths across GBs. Consequently, a simple p‐Si/TiO2/Pt heterojunction photocathode with controllable Ovac distribution in TiO2 shows a +400 mV onset potential shift and yields an applied bias photon‐to‐current efficiency of 5.9 %, which is the best efficiency reported among silicon photocathodes except for silicon homojunction.

Steering the Pathway of Plasmon‐Enhanced Photoelectrochemical CO2 Reduction by Bridging Si and Au Nanoparticles through a TiO2 Interlayer

“…The Si photocathode with a 20 nm thick TiO 2 layer shows better PEC activity, probably due to the enhanced passivation effect of the thicker TiO 2 layer according to the previous studies. [ 60–62 ] Moreover, the FE for CO production of Au/TiO 2 /n + p‐Si photocathode remains unchanged with the increase of thickness in the TiO 2 layer. One can therefore infer that the hot holes excited from the Au nanoparticle were unlikely to pass through the TiO 2 layer to the valence band of Si, considering the mean free path of the hot holes (5–10 nm) is smaller than the maximum thickness of TiO 2 layer (20 nm).…”

Bundle-Type Columnar Cu2O Photoabsorbers with Vertical Grain Boundaries Fabricated Using Instant Strike-Processed Metallic Seeds and Their Enhanced Photoelectrochemical Efficiency

“…Gong et al. reported that numerous GBs in polycrystalline TiO 2 can impede carrier transport because of excessive recombination, but oxygen vacancies with controllable GB distribution can promote carrier transport . For a typical photoelectrochemical reaction, the photoexcited carriers in the photoabsorbers are longitudinally moved to the electrolyte or the substrate by the external or built-in electric fields .…”

“…Gong et al reported that numerous GBs in polycrystalline TiO 2 can impede carrier transport because of excessive recombination, but oxygen vacancies with controllable GB distribution can promote carrier transport. 32 For a typical photoelectrochemical reaction, the photoexcited carriers in the photoabsorbers are longitudinally moved to the electrolyte or the substrate by the external or built-in electric fields. 33 Thus, as the best alternative for the absorber structure, a bundle structure of vertical-columnar crystals, where the GBs of the polycrystals are vertically wellaligned, is proposed (Figure 1c).…”

Identifying Reactive Sites and Surface Traps in Chalcopyrite Photocathodes

“…Understanding the atomic nature of reactive sites and surface traps is a key enabling step towards optimizing chemical conversion at semiconductor-liquid junctions. [1][2][3] The recent development of operando analysis tools has provided deep insights into the operation of specific semiconductor electrodes for solar-driven H 2 production via water splitting. [4][5][6][7] However, each material brings a unique atomic and electronic structure that requires the development of specific analysis tools and interpretation.…”