Energy-Band Alignment of BiVO₄ from Photoelectron Spectroscopy of Solid-State Interfaces

Abstract

The interface formation and energy-band alignment at interfaces between polycrystalline BiVO 4 and high-work-function RuO 2 and low-work-function Sn-doped In 2 O 3 (indium tin oxide) have been studied using photoelectron spectroscopy with in situ thin-film deposition of the contact materials. The Schottky barrier heights for both contact films differ by 0.85 eV, which is smaller than the difference in work function and the differences observed for other semiconducting oxides, indicating a partial Fermi-level pinning. On the basis of the present results and the comparison with other photoelectrochemically active oxides, the differences of band alignment obtained from solid/ electrolyte and from solid/solid interfaces, which can exhibit substantial differences, are discussed.

Pinning of the Fermi Level in CuFeO2 by Polaron Formation Limiting the Photovoltage for Photochemical Water Splitting

“…Contrarily, the 4.3 eV ITO work function is quite low, considering the value of 2.6 eV for E F – E VBM (Figure a). However, this work function agrees well with other values of ITO films deposited at room temperature . Another possible reason for the observed vacuum level offset could be Fermi level pinning.…”

“…From the secondary electron cut‐offs of the measured ultraviolet photoelectron (UP) spectra (Figure c), work functions of 5.2 and 4.3 eV were determined for the 2H CuFeO 2 pellet and the ITO film, respectively. The ITO work function, here, corresponds to earlier published ITO work functions . When combining the 5.2 eV CuFeO 2 work function with the value of 0.2 eV for E F – E VBM , an ionization potential of 5.4 eV is retrieved for the 2H CuFeO 2 pellet.…”

“…The ITO work function, here, corresponds to earlier published ITO work functions. [38,39] When combining the 5.2 eV CuFeO 2 work function with the value of 0.2 eV for E F -E VBM , an ionization potential of 5.4 eV is retrieved for the 2H CuFeO 2 pellet. Indeed, Omeiri et al determined through Mott-Schottky flat band measurements that the ionization potential of the (001) surface of a 3R CuFeO 2 single crystal amounts to 5.4 eV.…”

“…However, this work function agrees well with other values of ITO films deposited at room temperature. [38,41] Another possible reason for the observed vacuum level offset could be Fermi level pinning.…”

Analysis of the interfacial characteristics of BiVO4/metal oxide heterostructures and its implication on their junction properties

“…Previously, we performed a BiVO4/ITO interface experiment for which we found a downwards band bending of 0.16 eV and a barrier height of 1.96 eV. 52 However, the ITO layer was deposited at room temperature so that the EF-EVBM was limited to 2.5 eV. Here, BiVO4 was heated to 400 °C before each ITO deposition step, while maintaining a pure argon atmosphere.…”