Lattice-Matched Ta₃N₅/Nb₅N₆ Interface Enables a Bulk Charge Separation Efficiency of Close to 100%

The interface between the semiconductor light absorber and the metal electrode is critical for facilitating the extraction of photogenerated charges in photoelectrodes. Achieving a lattice-matched semiconductor/electrode interface with low defect density is highly desirable but remains a challenge for Ta₃N₅ photoanodes. In this study, we synthesized niobium nitride thin film electrodes with controllable crystallographic phases to achieve a lattice-matched Ta₃N₅/Nb₅N₆ back contact. This results in an enhanced crystallinity of the Ta₃N₅ film and reduced interfacial defect density. Consequently, the photoanode with the lattice-matched back contact attains a record half-cell solar-to-hydrogen conversion efficiency of 4.1%, attributed to the bulk carrier separation efficiency of nearly 100%. This work highlights lattice-matching as an effective strategy to enhance the efficiency of thin film-based solar energy conversion devices.