Microscopy techniques demystify secrets of twin domains in methylammonium lead iodide

Optoelectronics rely on the ability of materials to convert between light and electronic signals efficiently. One material, methylammonium lead iodide (MAPbI₃), shows promise as a lower cost alternative to today’s silicon-based photovoltaics. Several recent studies have observed what appeared to be twin domains, in which two crystals form next to one another in symmetry within MAPbI₃. One new study looks to conclusively characterize these features of MAPbI₃, with potential to one day help materials scientists use twin domains to affect material properties.

Liu et al. used band excitation force microscopy to describe how twin domains function within MAPbI₃ crystals. The findings revealed the effects of twin domains on the movement of ions in crystals, while putting to rest a debate over whether MAPbI₃’s ferroelectricity is at the root of twin domain formation.

Using band excitation piezoresponse force microscopy (PFM) and band excitation contact Kelvin probe force microscopy, the group eliminated topographic cross-talk in the hybrid perovskites and determined that it is MAPbI₃’s ability to spontaneously take on strain, not its ferroelectricity, that contributes to observed twin domains in PFM.

Although ferroelectricity is absent in them, twin domains still respond to applied electric bias because of ion diffusion, resulting in dynamic contrast of twin domains under electric bias, leading the authors to propose that twin domains can affect ion migration.

The authors stated that they hope their results will encourage the research community to further investigate the possibility of MAPbI₃’s twin domains to manipulate ion migration and photovoltaic performance.

Source: “Dynamic behavior of CH₃NH₃PbI₃ perovskite twin domains,” by Yongtao Liu, Liam Collins, Alex Belianinov, Sabine M. Neumayer, Anton V. Ievlev, Mahshid Ahmadi, Kai Xiao, Scott T. Retterer, Stephen Jesse, Sergei V. Kalinin, Bin Hu, and Olga S. Ovchinnikova, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5041256 .