Local dynamics in hybrid perovskites by solid-state NMR

Fast and mostly unforeseen emergence of hybrid perovskites as promising photovoltaic materials produced a massive surge of research activity. The motivation driving so many research groups around the world originates in their enormous promise for production of inexpensive and versatile solar cells. Indeed, the idea of producing a light converting device by wet chemistry techniques is very appealing. Rapid development of this competitive research field and the urgency for understanding on a deep level the mechanisms governing functioning of the hybrid halogen perovskites has stimulated an extensive use of numerous spectroscopic techniques. It has been realized, that understanding of local dynamics in the hybrid halogen perovskites will help in a targeted design of new materials and ultimately result in a production of better functioning devices with desired properties. Solid-state NMR is an effective and well-established spectroscopic technique, providing powerful framework of tools for elucidating details of local dynamics over a wide range of frequencies. The first part of this article makes an overview of the NMR dynamic toolbox, with a focus on techniques that are particularly suitable for evaluation of local molecular motion in hybrid halogen perovskite: relaxation time measurements, spectral line-shape analysis, and 2D exchange NMR for slow processes. An outline of NQR application for dynamic studies is also included. Second part of the article offers current literature accounts on evaluation of dynamics in hybrid perovskites by solid-state NMR and NQR and gives an outlook on the possible future developments.