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

Photoactive bismuth vanadate (BiVO₄) thin films were deposited by reactive co-magnetron sputtering from metallic Bi and V targets. The effects of the V-to-Bi ratio, molybdenum doping and post-annealing on the crystallographic and photoelectrochemical (PEC) properties of the BiVO₄ films were investigated. Phase-pure monoclinic BiVO₄ films, which are more photoactive than the tetragonal BiVO₄ phase, were obtained under slightly vanadium-rich conditions. After annealing of the Mo-doped BiVO₄ films, the photocurrent increased 2.6 times compared to undoped films. After optimization of the BiVO₄ film thickness, the photocurrent densities (without a catalyst or a blocking layer or a hole scavenger) exceeded 1.2 mA/cm² at a potential of 1.23 V_RHE under solar AM1.5 irradiation. The surprisingly high injection efficiency of holes into the electrolyte is attributed to the highly porous film morphology. This co-magnetron sputtering preparation route for photoactive BiVO₄ films opens new possibilities for the fabrication of large-scale devices for water splitting.