Researchers Boost Thin-Film SnS Solar Cell Efficiency With Ultra-Thin Germanium Oxide Layer – Chonnam National University (South Korea)

Researchers from Chonnam National University in South Korea have made a significant breakthrough in improving the performance of thin-film solar cells, a development that could have broad implications for renewable energy and other electronic technologies. Their study, published online in the journal Small on September 19, 2025, demonstrates that introducing an ultra-thin layer of germanium oxide (GeOx) between the molybdenum back contact and the tin monosulfide (SnS) absorber layer dramatically enhances device efficiency and stability.

Tin monosulfide, or SnS, is a promising material for thin-film solar cells due to its abundance, low cost, and non-toxic nature. Unlike other thin-film designs that rely on scarce and expensive elements such as indium, gallium, and tellurium, SnS aligns with the United Nations’ Sustainable Development Goals and offers favorable optical and electronic properties for sunlight harvesting. Despite its potential, the performance of SnS-based devices has historically been limited by structural defects and unwanted chemical reactions at the rear-contact interface, where the SnS layer connects to the metal electrode. These defects reduce the efficiency of charge collection and limit overall power conversion.

The research team, led by Professor Jaeyeong Heo and Dr. Rahul Kumar Yadav, addressed these long-standing challenges through precise interface engineering. They developed a 7-nanometer-thick GeOx interlayer using a vapor transport deposition process that leverages the natural oxidation behavior of a thin germanium film. This approach is not only precise but also scalable and industry-friendly, making it feasible for large-scale production.

The GeOx layer acts on multiple fronts to improve device performance. It suppresses deep-level defects, blocks unwanted diffusion of sodium, and prevents the formation of resistive molybdenum disulfide phases that can occur during high-temperature fabrication. These effects collectively enhance the quality of the SnS absorber layer, resulting in larger and more uniform grains, better charge transport, and reduced electrical losses. As a result, the power conversion efficiency of the solar cells increased from 3.71% in standard devices to 4.81%, representing one of the highest efficiencies reported for vapor-deposited SnS solar cells.

The implications of this advancement extend beyond solar energy. Metal/semiconductor interfaces are critical in a wide range of technologies, including thin-film transistors, thermoelectric devices, sensors, flexible electronics, photodetectors, and memory devices. Optimizing these interfaces can improve contact resistance, energy conversion efficiency, charge transfer, and overall device stability. Professor Heo noted that mastering metal/semiconductor interfaces is central to advancing next-generation electronics and energy technologies.

This breakthrough underscores the importance of interface engineering in renewable energy research and demonstrates how a small, precisely engineered layer can significantly enhance the performance of sustainable and scalable energy solutions. By improving the efficiency and stability of thin-film SnS solar cells, the study offers a pathway to more affordable, non-toxic, and widely deployable solar energy technologies, supporting the global transition toward clean and sustainable energy.