Korean Researchers Achieve Efficiency Breakthrough in Tin Monosulfide Solar Cells

As global demand for clean and scalable energy solutions accelerates, solar power continues to gain prominence, particularly through advances in next-generation cell technologies. Researchers are increasingly focusing on thin-film solar cells as cost-effective and flexible alternatives to conventional crystalline silicon. Among these, tin monosulfide (SnS) has attracted attention as a non-toxic, earth-abundant material aligned with sustainability goals, though practical performance has long lagged behind theoretical potential.

A research team from Chonnam National University (CNU) in South Korea has now reported a significant step forward in overcoming this limitation. Led by Professor Jaeyeong Heo and Dr. Rahul Kumar Yadav, the team has developed a novel rear-contact interface design that substantially improves the efficiency of thin-film SnS solar cells. Their findings were published online in the journal Small on September 19, 2025.

The breakthrough centers on inserting an ultra-thin, 7-nanometer layer of germanium oxide (GeOx) between the molybdenum back electrode and the SnS absorber layer. This GeOx interlayer is formed through a scalable vapor transport deposition process, leveraging the natural oxidation of a thin germanium film. Despite its minimal thickness, the layer addresses several persistent issues at the metal–semiconductor interface.

According to the researchers, the GeOx layer suppresses deep-level defects, blocks unwanted sodium diffusion, and prevents the formation of resistive molybdenum disulfide during high-temperature processing. These improvements result in better crystal quality, enhanced charge transport, and reduced electrical losses.

As a result, the power conversion efficiency of SnS solar cells increased from 3.71% in conventional designs to 4.81%, representing one of the highest reported efficiencies for vapor-deposited SnS devices. Beyond photovoltaics, the interface engineering approach may also benefit thin-film transistors, thermoelectric devices, sensors, and flexible electronics, highlighting its broader technological relevance.