Converting sunlight into renewable fuels is a central goal of clean energy research. One promising pathway is photoelectrochemical (PEC) water splitting, which uses semiconductor electrodes to harness sunlight and split water into its two components: hydrogen, a clean fuel, and oxygen. Among the candidate materials, tantalum nitride (Ta₃N₅) has long been attractive because it can absorb visible light efficiently. However, its performance has been limited by poor electrical conductivity, requiring thick films that use large amounts of tantalum—an expensive and rare element.
In a new study published in Small, researchers at the Department of Chemistry, National Taiwan University, present a breakthrough approach that tackles this challenge. By starting with a chemically engineered precursor called bixbyite-type Ta₂N₃, the team developed ultrathin Ta₃N₅ photoanodes that operate efficiently while using far less tantalum. Unlike conventional methods, this strategy naturally produces small amounts of highly conductive subnitride phases at the interface with the silicon support. Rather than being detrimental, these conductive impurities act like “highways” for charge carriers, helping electrons and holes move more efficiently and reducing losses that usually limit Ta₃N₅.
The resulting photoanodes show significant improvements in charge separation and photocurrent output, even at reduced thicknesses. This means that less tantalum is required while maintaining, or even enhancing, performance. Through advanced structural, optical, and electrochemical characterization, the researchers confirmed that the improved efficiency comes from smart interface engineering between Ta₃N₅ and silicon.
“By rethinking how we design the interface, we can make Ta₃N₅ much more efficient without relying on thick, resource-intensive films and substrates,” says Dr. Chang-Ming Jiang, an assistant professor in the Department of Chemistry and the corresponding author of the study. “This was only possible because NTU invested in a state-of-the-art reactive sputter deposition system, which allowed us to access the metastable Ta₂N₃ precursor. That infrastructure support was crucial for enabling this discovery.”
Beyond water splitting, the insights from this work highlight a versatile design principle for other thin-film semiconductors, offering a blueprint for more efficient and sustainable solar energy technologies.
