Bismuth manganate (BMO) thin films with bismuth oxide nanoislands, prepared via sol–gel, on fluorine-doped tin oxide substrates, show a tenfold increase in photocurrent as compared to pristine BMO thin films. Overlayers with suitable band alignment can therefore be crucial for improving the performance of photoabsorbers like BMO.

Photoelectrochemical (PEC) water splitting is a promising method for the energy transition. However, it is still hampered because the performance of the electrodes is too low. Herein, bismuth manganate (BMO) is investigated as a photoanode absorber material for PEC. BMO thin films are prepared by a sol–gel method with and without a bismuth oxide (BO) overlayer. It is found that the BO overlayer forms BO nanoislands after annealing. Under visible light illumination, BMO with BO nanoislands results in a nearly tenfold increase of the current density compared to pristine BMO at the same applied potential. This increased performance is related to a decrease in the charge transfer resistance and in the amount of recombinations based on the formation of a favorable heterojunction between BMO and BO. The application of overlayers on electrode materials in combination with suitable band alignment is an effective strategy to improve the performance of PEC electrodes.