Atomically thin two-dimensional organic-inorganic hybrid perovskites

Flat perovskite crystals Bulk crystals and thick films of inorganic-organic perovskite materials such as CH 3 NH 3 PbI 3 have shown promise as active material for solar cells. Dou et al. show that thin films—a single unit cell or a few unit cells thick—of a related composition, (C 4 H 9 NH 3 ) 2 PbBr 4 , form squares with edges several micrometers long. These materials exhibit strong and tunable blue photoluminescence. Science , this issue p. 1518