Electronic Structure of Monoclinic BiVO₄

Abstract

Figure S1. XRD of CVD grown BiVO 4 (black) thin film grown on FTO coated glass substrate. Also provided are reference peaks of FTO and monoclinic scheelite (ms) BiVO 4 .

Role of Hydrogen in Defining the n-Type Character of BiVO4 Photoanodes

“…23 Furthermore, these findings are consistent with the model of Van de Walle,48 in which the character of the H int defect is defined by the position of the Fermi level with respect to the universal hydrogen level, which is at the same energy as an electron in the standard hydrogen electrode (SHE). In the case of BiVO 4 , for which the CBM energy is 0.1 -0.3 eV below SHE, 6,16 interstitial hydrogen should act as a donor, as observed in our experiments. The higher carrier concentration created by H 2 annealing can also explain the improved PEC performance presented in Fig.…”

“…Therefore, we consider the possibility that this absorption increase is due to d-d transitions of V 4+ (3d 1 ), which should have transition energies in the range of 1 -2 eV. 6,37 It is now well established that electron small polarons in BiVO 4 are energetically favoured over delocalized electrons in the conduction band. [10][11][12] Such electron small polarons localize at V sites, leading to a change of formal oxidation state from V 5+ (3d 0 ) to V 4+ (3d 1 ), the concentration of which will increase with increasing electron polaron concentration.…”

“…Bismuth vanadate (BiVO 4 ) is one of the most actively investigated oxide semiconductors for PEC energy conversion due to its moderate indirect bandgap of 2.5 eV, 5 favourable conduction band position, 6 and relatively long photocarrier lifetimes. [6][7][8] However, poor majority carrier transport, arising from formation of electron small polarons, has been identified as one of the primary limitations on its PEC performance.…”

“…[6][7][8] However, poor majority carrier transport, arising from formation of electron small polarons, has been identified as one of the primary limitations on its PEC performance. [9][10][11][12] To overcome this issue, the best-performing BiVO 4 films incorporate n-type dopants, such as tungsten or molybdenum, to increase n-type conductivity, 13 nanostructured architectures to decrease transport lengths while increasing semiconductor/electrolyte junction areas, [14][15][16] or carrier selective contacts to reduce photocarrier recombination rates.…”

Assembly and Photocarrier Dynamics of Heterostructured Nanocomposite Photoanodes from Multicomponent Colloidal Nanocrystals

“…[3,5] It has a moderate bandgap of 2.5 eV and an energetically low-lying valence band position. [6,7] However, it suffers from exceptionally small majority carrier mobilities due to formation of electron small polarons, [8][9][10] photochemical instabilities associated with localization of holes near its surface, [11] and relatively slow injection of holes across the semiconductor/electrolyte interface. While incorporation of a catalyst on the surface can improve stability and increase OER activity, reducing photocarrier recombination in the material calls for strategies to promote physical charge separation and electron extraction.…”