Organic-inorganic perovskites are important light-harvesting materials and have showed promise for use in optoelectronic devices. However, most perovskite devices reported recently, such as photodetectors, are based on polycrystalline films of perovskites. The large grain boundaries and high number of defects in such films hinder the fabrication of high-performance devices.

Huanli Dong, Wenping Hu, and colleagues, Chinese Academy of Science, Beijing, have synthesized large amounts of high-quality single crystals of the perovskite CH₃NH₃PbI₃ through a simple solution immersion method. First, PbI₂ thin films were spincoated onto a glass substrate, then immersed into a high-concentration solution of CH₃NH₃I in isopropanol. The reactants then formed the perovskite, which was left in the solution to recrystallize for 12–36 hours.

The obtained single crystals showed nanowire and nanoplate morphologies, which belonged to the same tetragonal phase. The size of the CH₃NH₃PbI₃ crystals could be tuned easily by adjusting the recrystallization time. Based on the CH₃NH₃PbI₃ crystals, high-performance photodetectors were fabricated with an on/off ratio up to 103. This is two orders of magnitude higher than that of previous CH₃NH₃PbI₃ film devices.

• Perovskite Photodetectors based on CH₃NH₃PbI₃ single crystals,
  Wenping Hu, Xiang Qin, Yifan Yao, Huanli Dong,
  Chem. Asian J. 2016.
  DOI: 10.1002/asia.201600430