Huub J. M. de Groot

A Lanthanum ion (La 3+ ) incorporation strategy is implemented to modify Ba 2 Bi 2 O 6 ‐based double perovskite photoelectrodes. X‐ray diffraction (XRD) characterization shows that highly crystalline Ba 2 La 0.4 Bi 1.6 O 6 double perovskites with the space group I 2 /m are successfully prepared. UV–vis absorption spectra and the Tauc‐plot reveal an optical band gap E g ≈1.57 ± 0.01 eV. A thickness dependence of the photoelectrodes photoelectrochemical (PEC) performance shows that the submicron (≈1 µm) 4‐times spin‐coated thin film photoelectrode displays strong p‐type conductivity, which delivers an encouraging photocurrent density of 0.88 mA cm −2 at 0.25 V RHE under AM 1.5G illumination. 10‐times coated and 20‐times coated medium thick (125.8–197 µm) photoelectrodes that exhibit moderate p‐type conductivity, show further enhanced photocurrent densities of 1.5 mA cm −2 at 0 V RHE . In contrast, charge recombination centers existing in a standard thick pellet (≈500 µm) Ba 2 La 0.4 Bi 1.6 O 6 photoelectrode can quench photo‐generated charge carriers and greatly undermine PEC activities. The approach to doping at the Bi(III) sites contrasts with earlier efforts that focus on doping at the Bi(V) sites and thus paves the way for further tailoring a family of novel promising photocathode materials for efficient solar‐water conversion devices.