Band structure engineering and defect control of Ta₃N₅ for efficient photoelectrochemical water oxidation

Ta₃N₅ is a promising photoanode material with a theoretical maximum solar conversion efficiency of 15.9% for photoelectrochemical water splitting. However, the highest applied bias photon-to-current efficiency achieved so far is only 2.72%. To bridge the efficiency gap, effective carrier management strategies for Ta₃N₅ photoanodes should be developed. Here, we propose to use gradient Mg doping for band structure engineering and defect control of Ta₃N₅. The gradient Mg doping profile in Ta₃N₅ induces a gradient of the band edge energetics, which greatly enhances the charge separation efficiency. Furthermore, defect-related recombination is significantly suppressed due to the passivation effect of Mg dopants on deep-level defects and, more importantly, the matching of the gradient Mg doping profile with the distribution of defects within Ta₃N₅. As a result, a photoanode based on the gradient Mg-doped Ta₃N₅ delivers a low onset potential of 0.4 V versus that of a reversible hydrogen electrode and a high applied bias photon-to-current efficiency of 3.25 ± 0.05%. [Figure not available: see fulltext.]