 Many of the most sensitive x-ray detectors are based on toxic elements such as lead, limiting their safe applications. Here, the authors report the realization of sensitive x-ray detectors based on solution-grown thick bi-i-bi-i-3 bi-i-vander-walls heterostructures, showing a detection limit down to 34-ing ES1 and high stability. This article was authored by Ren Cheung-chwong, Songhua CAI, Xinxia Mai, and others.