When making mixed-halide perovskite films for use in solar cells, bromide-rich domains crystallize faster than iodide-rich ones do, leading to defects. Adding a molecule tuned to bind selectively to bromide-bound lead synchronizes the crystallization rates, yielding uniform films, better operating stability and a more-efficient perovskite–organic tandem.

Records of war extracted from news reports have shaped what researchers know about violence. Satellite images could transform that understanding — if access stays open.

One-to-one phone sessions substantially increased students’ numeracy test scores in low- and middle-income countries that experience emergencies that disrupt schooling.

Across five randomized trials in India, Kenya, Nepal, the Philippines and Uganda, weekly 20-minute mobile-phone-call tutorials produced large learning gains for primary-school children during school closures caused by the COVID-19 pandemic. Governments can keep children learning through societal shocks using this approach, which combines low-cost, high-access mobile-phone technology with high-quality tutoring targeted to each child’s learning level.