Thin-film solar cell made from non-toxic, Earth-abundant copper, barium, tin, sulfur, and selenium, is 28% efficient

https://www.metaltechnews.com/story/2025/04/16/tech-metals/mexican-thin-film-solar-doubles-efficiency/2231.html

"anti-reflection coating reduces amount of light lost at surface, allows more solar energy to enter cell... replaced molybdenum with nickel in back contact layer, improving cell's electrical conductivity, allowing current to flow more freely... back surface field layer made of copper iodide, strengthening electric field at the junction, reducing electron recombination and increasing overall performance... fine-tuned thickness/ carrier density of each layer, optimizing how charge moves within cell"

Related: Improving the performance of Cu₂SrSnS₄ solar cells with inorganic hole transport layers
https://techxplore.com/news/2025-05-cusrsns-solar-cells-inorganic-hole.html