Engineering Interfacial Silicon Dioxide for Improved Metal–Insulator–Semiconductor Silicon Photoanode Water Splitting Performance

Abstract

Silicon photoanodes protected by atomic layer deposited (ALD) TiO2 show promise as components of water splitting devices that may enable the large-scale production of solar fuels and chemicals. Minimizing the resistance of the oxide corrosion protection layer is essential for fabricating efficient devices with good fill factor. Recent literature reports have shown that the interfacial SiO2 layer, interposed between the protective ALD-TiO2 and the Si anode, acts as a tunnel oxide that limits hole conduction from the photo-absorbing substrate to the surface oxygen evolution catalyst. Here-in we report a significant reduction of bilayer resistance, achieved by forming stable, ultrathin (< 1.3 nm) SiO2 layers, allowing fabrication of water splitting photoanodes with hole conductances near the maximum achievable with the given catalyst and Si substrate. Three methods for controlling the SiO2 interlayer thickness on the Si(100) surface for ALD-TiO2 protected anodes were employed: (1) TiO2 deposition directly on an HF-etched Si(100) surface, (2) TiO2 deposition after SiO2 atomic layer deposition on an HF-etched Si(100) surface, and (3) oxygen scavenging, post-TiO2 deposition to decompose the SiO2 layer using a Ti overlayer. Each of these methods provides a progressively superior means of reliably thinning the interfacial SiO2 layer, enabling the fabrication of efficient and stable water oxidation silicon anodes.

Hierarchical CdS Nanorod@SnO2 Nanobowl Arrays for Efficient and Stable Photoelectrochemical Hydrogen Generation

“…It has been documented that the thickness of the protective SiO 2 layer is essential to the performance of the photoanodes since a thick SiO 2 layer may increase the series resistance while a thin SiO 2 layer may not be able to provide effective protection despite its positive effect on the PEC performance due to surface passivation . For example, an optimized thickness for the protective layer was reported to be around 2 nm in certain cases . Therefore, it would be worthwhile to further explore controllable solution methods to achieve a thinner SiO 2 layer to provide effective surface passivation without considerably sacrificing photocatalytic performance.…”

Solid Electrolyte Interphase on Native Oxide-Terminated Silicon Anodes for Li-Ion Batteries

“…To test this hypothesis, we performed LSV at 0.1 mV/s in the Teflon cone cell 44,45 utilizing n-type doped single crystalline Silicon carbide (SiC). SiC is electrochemically nonactive, sufficiently conducting (0.02-0.1 U$cm), and the surface oxidation is limited.…”

“…In order to relate our structural findings to electrochemical measurements, we performed LSV of an oxide-terminated Si wafer at 0.1 mV/s with the same half-cell configuration in a Teflon cone cell. 44,45 This cell was utilized because it eliminates parasitic currents, only the active material (and inert Teflon) is in contact with the electrolyte, and it has a well-defined surface area (1.27 cm 2 ). This yields precision voltammetry.…”

“…For ex situ XPS, the Si anodes were galvanostatically cycled at 50 mA/cm 2 to the pre-set potentials (0.8, 0.7, 0.6, 0.3, and 0.2 V) and then held at the potential for 2 h. For LSV measurements, a Teflon cone electrochemical cell was used. 44,45 The working electrode was a (001)-terminated n-type doped Si wafer with a resistivity of 0.001-0.005 U$cm. A 2 nm-thick Ti adhesive layer and 100 nm-thick Cu layer were evaporated on the back side of the Si wafer to ensure good electrical contact.…”

Time‐Resolved Structural Kinetics of an Organic Mixed Ionic–Electronic Conductor

“…This cell is based on that developed for precision electrochemistry for electrochemical energy storage and is readily adopted for the present study. [ 21–24 ] The PEEK wall thickness (1.5 mm) machined down to a knife edge was sufficiently thin that the attenuation of the scattered intensity was not prohibitive (Figure S1b, Supporting Information). Due to the machined knife edge, attenuation of the low angle incident beam was minimal, scattered intensity was increasingly attenuated with increasing scattering angle, reaching ≈50% attenuation at 25°, due to a PEEK pathlength of ≈1.1 mm.…”