Illuminated from back or front? Insight into factors affecting the efficiency of BiVO4 photoanode

For a long time, it is generally believed that BiVO4 photoanode will obtain higher photocurrent under back-side illumination, the explanation for this is the diffusion length of electrons is shorter in this condition. However, for an n-type semiconductor, the diffusion length of majority carriers, that is, electrons, should not be the main reason affecting the photocurrent, while the diffusion length of minority carriers and the intensity of built-in electric field are the key factors. In this paper, we proved this by comparing the photoelectrochemical performance of BiVO4 films with different thicknesses and densities. More importantly, we found that it produced a potential drop on the polycrystalline boundary, which leads to the interface electric field cannot increased with the increasing of applied potential, this is exactly the reason for limiting the thickness and efficiency of BiVO4 photoelectrode. Based on this, we proposed a carriers transport model more suitable for polycrystallineelectrode.