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.