Role of Gd in Enhancing the Charge Carrier Mobility of Spray–Deposited BiVO<inf>4</inf> Photoanodes

Abstract

The emergence of BiVO4 as one of the most promising photoanodes for solar water splitting is largely driven by the success in dopant introduction and optimization to improve its photoelectrochemical performance. To this end, although less commonly used, several trivalent ions (e.g., In3+, Gd3+) that substitute Bi3+ have also been demonstrated to be effective dopants, which can increase the photocurrent of BiVO4 photoanodes. However, the main factor behind such improvement is still unclear as various explanations were proposed in the literature. Herein, Gd3+ is introduced to substitute Bi3+ in spray-deposited BiVO4 films, which enables up to a ∼2-fold photocurrent increase. Further analysis suggests that Gd-doping enhances the carrier separation in BiVO4 and does not affect the catalytic and optical properties. Indeed, time-resolved microwave conductivity measurements reveal that the carrier mobility of BiVO4 is increased by 50% with the introduction of Gd, while the carrier lifetime is unaffected. This mobility increase is rationalized to be a result of a higher degree of monoclinic lattice distortion in Gd-doped BiVO4, as evident from the X-ray diffraction and Raman spectroscopy data. Overall, these findings provide important insights into the nature and the underlying role of Gd in improving the performance of BiVO4.