Science 349, 1518–1521 (2015)

Hybrid organic–inorganic perovskites, such as CH3NH3PbI3, are a class of semiconducting material that have attracted considerable research attention in recent years due to their potential in photovoltaic applications. The materials can be used to create solution-processed devices and rapid improvements in their capabilities mean that perovskite solar cells currently offer power conversion efficiencies of over 20%. Peidong Yang and colleagues at the University of California, Berkeley, Lawrence Berkeley National Laboratory and ShanghaiTech University have now shown that these layered materials can be grown as atomically thin two-dimensional sheets.

The researchers synthesized sheets of the hybrid perovskite (C4H9NH3)2PbBr4 by dropping a dilute precursor solution on a silica surface and allowing it to dry under mild heating. With the approach, micrometre-sized crystals were created that had well-defined square shapes and were a single or a few unit cells thick. Detailed analysis of the materials revealed that they exhibit a structural relaxation that shifts their bandgap compared with the bulk material. The two-dimensional crystals also exhibit a blue photoluminescence that could be tuned by varying the thickness of the sheets or their composition.