Improved Charge Carrier Dynamics by Unconventional Doping Strategy for BiVO₄ Photoanode

Bismuth vanadate (BiVO₄) is one of the promising photoanodes for solar fuel production, but it faces the challenge of poor charge separation due to its sluggish charge transport and short diffusion length. The ability to regulate charge separation is pivotal for obtaining high efficiency of BiVO₄. Herein, an unconventional acceptor doping strategy is proposed for the first time, demonstrating its effectiveness in enhancing charge carrier dynamics. Introducing the Al³⁺ ions into BiVO₄ induced a decrease in carrier concentration but an increase in the diffusion length and carrier lifetime due to the reduced chance of encountering an electron-hole pair. Furthermore, decreasing carrier concentration leads to a widened space charge layer, enabling facile charge transport and separation. The optimized 0.5 at% Al-doped BiVO₄ (Al:BVO_0.5) exhibited ≈3.5 and 2.6 order of magnitude increase in diffusion length and in carrier lifetime, respectively, compared to pristine BiVO₄, achieving a photocurrent density of 3.02 mA cm⁻² at 1.23 V_RHE (V versus reversible hydrogen electrode) under AM 1.5 G illumination. This research provides a new understanding of semiconductor physics and design principles for more efficient photoanodes.