Researchers at the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, with IIT Hyderabad under the Department of Science and Technology, built an eco-friendly lead-free photodetector. It uses the double perovskite Cs2AgBiBr6 with cheap carbon electrodes, is self-powered, responds strongly to visible light and keeps over 90% performance after 60 days. Made by a single room-temperature coating step, it suits electronics, security, industrial monitoring and biomedical imaging.