Researchers from Tohoku University and the University of Science, Vietnam National University - Ho Chi Minh City have made a significant breakthrough in the field of green energy conversion by identifying critical factors in two-dimensional (2D) Janus heterobilayers. The study highlighted a WS₂-SMoSe heterobilayer with an impressive solar-to-hydrogen conversion efficiency of 16.62%, surpassing many existing materials. Photocatalytic water splitting, utilizing sunlight to produce hydrogen fuel, is crucial for reducing greenhouse gas emissions and combating global warming. Traditional materials face challenges such as low efficiency and electron-hole recombination, which the Janus heterobilayers address with their unique internal electric fields. The team explored 20 different pairings of Janus and transition-metal dichalcogenide materials, demonstrating the promise of Janus heterobilayers for water splitting. These materials feature different chalcogenide elements on each side, creating strong internal electric fields that enhance charge separation, leading to improved photocatalytic performance. The researchers likened the process of combining TMDCs with Janus layers to building with LEGO, emphasizing the vast configurations and the efficiency in identifying optimal material combinations. Lead author Nguyen Tran Gia Bao highlighted the efficient and precise methodology developed by the team for identifying promising material combinations, expediting the discovery process. Nguyen Tuan Hung expressed the importance of the findings in supporting sustainable hydrogen production, with a commitment to further exploring material combinations in future research. The study was published in ACS Applied Energy Materials, offering a fresh perspective on sustainable energy and laying the groundwork for future advancements in the field.