Tantalum Nitride‐Enabled Solar Water Splitting with Efficiency Above 10%

Abstract Designing photoanode semiconducting materials with visible‐light absorption and minimal charge‐carrier recombination for achieving efficient solar‐to‐hydrogen (STH) conversion is challenging. Here, hybrid Ta 3 N 5 nanorods and thin films are developed on transparent GaN/Al 2 O 3 substrates. A Ta 3 N 5 photoanode with a loaded cocatalyst achieves the best current density, i.e. 10.8 mA cm −2 , at 1.23 V versus the reversible hydrogen electrode under simulated AM 1.5G solar illumination. In a tandem configuration with dual‐CuInSe 2 photovoltaic cells, this semi‐transparent photoanode achieves a reproducible STH energy conversion efficiency of ≈12% (the highest among photocatalytic materials), and remains at more than 10% for 6.7 h of tandem device operation. Detailed transient absorption spectroscopy and theoretical analysis indicates that this high performance originates from efficient light absorption and hole utilization inside the Ta 3 N 5 material. The results show the feasibility of suppressing dominant optical and charge‐carrier‐ recombination losses by using nanostructured visible‐light‐absorbing materials for practical STH conversion.