Doping properties of monoclinic BiVO4studied by first-principles density-functional theory

Abstract

The intrinsic and extrinsic doping properties of BiVO 4 , i.e., the formation energies and transition energy levels of defects and impurities, have been studied systematically by first-principles density-functional theory. We find that for doping caused by intrinsic defects, O vacancies are shallow donors and Bi vacancies are shallow acceptors.However, these defects compensate each other and can only lead to moderate n-type and p-type conductivities at Bi-rich and O-rich growth conditions, respectively. To obtain BiVO 4 with high n-type and p-type conductivities, which are required for forming ohmic contacts, extrinsic doping using foreign impurities is necessary. Our results reveal that Sr, Ca, Na, and K atoms on Bi sites are very shallow acceptors and have rather low

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

“…As described above, native defect theory would predict that material synthesized under Orich conditions, which is the typical environment used for formation of BiVO 4 , should exhibit p-type character. 18 Our finding that hydrogen defects are present in as-synthesized BiVO 4 can explain the experimental observation that as-grown BiVO 4 is nearly always n-type. 8 The source of this hydrogen could be from decomposition of metal-organic precursors during formation and/or from water in the annealing environment, which is often laboratory air.…”

“…In particular, density functional theory (DFT) calculations by Yin et al predict that BiVO 4 should have p-type character when synthesized under O-rich conditions and n-type character when synthesized under O-poor/Bi-rich conditions. 18 In contrast, experimentally synthesized films, which are typically annealed at high temperature for long times in oxygen or air (i.e. under O-rich conditions), consistently exhibit n-type conductivity.…”

Determination of the Intrinsic Defect at the Origin of Poor H2 Evolution Performance of the Monoclinic BiVO4 Photocatalyst Using Density Functional Theory

“…21 Previous experimental works have reported band gaps in the 2.4-2.6 eV range of monoclinic BiVO 4 and theoretical calculations based on density functional theory (DFT) using standard GGA exchange-correlation functional like Perdew-Burke-Emzerhof (PBE) were performed for validation attempts. 15,22 However, more accurate calculations using hybrid functionals like HeydScuseria-Ernzerhof (HSE06) predicted a band gap energy around 3.0 eV. 23 This observation was surprising because semi-local GGA functionals generally strongly underestimate the band gap of semiconductors, while hybrid functionals like HSE06 are well known to give better agreement with experiment.…”

“…13 Doping by introducing an extrinsic defect through the addition of a transition-metal cation or an anion can increase the carrier density and thus improve the conductivity for optimum photocatalytic performance. Following 4 this strategy, numerous studies and research efforts have been focused on doping BiVO 4 with Mo and W. [14][15][16][17] This effect has been extended as well to intrinsic doping defined as native defects. Some studies suggested that this oxide can be stoichiometric at 1 atmospheric oxygen pressure, while oxygen vacancies might be created in reducing conditions.…”

BiVO4 photoanodes for water splitting with high injection efficiency, deposited by reactive magnetron co-sputtering

“…18 Incorporation of Mo into BiVO 4 increases the carrier density and distorts the VO 4 tetrahedron, resulting in a local internal electric field. 19 It has also been observed that Mo is better suited than the commonly used W for the n-type doping of BiVO 4 . 20 In this work, we systematically investigated the deposition of BiVO 4 films by a reactive magnetron sputtering process.…”