Do more with less—reducing material usage in light-driven energy conversion

Researchers from the Department of Chemistry, National Taiwan University, have developed a new synthesis route for ultrathin photoanodes, which enables a 100 nm tantalum nitride layer to outperform much thicker films fabricated through conventional oxide precursors.

In the search for sustainable energy solutions, photoelectrochemical water splitting offers a promising route to convert sunlight into hydrogen fuel. Among the semiconductor materials investigated for this purpose, tantalum nitride (Ta₃N₅) stands out due to its ideal bandgap and strong visible light absorption.

However, its practical application has been hindered by poor charge transport properties, which typically require thick films and large amounts of tantalum—an expensive and scarce metal.

In a study published in Small, researchers from National Taiwan University report a novel strategy to construct efficient Ta₃N₅ photoanodes using a chemically engineered precursor layer, bixbyite-type Ta₂N₃.

Unlike conventional synthesis routes, this approach enables the formation of ultrathin, high-performance Ta₃N₅ films on silicon substrates while significantly reducing tantalum usage. The resulting photoanodes exhibit improved charge separation and enhanced photocurrent generation, achieving performance levels previously only accessible with much thicker films.

“Ta₂N₃ is a metastable material, meaning it readily transforms into Ta₃N₅, a semiconducting nitride widely employed in light-driven energy conversion systems,” says Chang-Ming Jiang, the study’s principal investigator.

“Using Ta₂N₃ as a precursor also produces trace amounts of subnitride impurities at the interface with silicon. These impurity phases are highly conductive and beneficial for extracting photogenerated carriers from Ta₃N₅.”

Through a combination of structural, optical, and electrochemical characterization, the study demonstrates how interface engineering between Ta₃N₅ and silicon can overcome long-standing limitations in carrier transport.

This advancement opens new directions for scalable solar-driven hydrogen production with lower material costs and improved efficiency.

The work not only deepens the understanding of nitride semiconductor interfaces but also offers a broadly applicable strategy for designing next-generation photoelectrodes.