Pressure-Induced Phase Transformation and Band-Gap Engineering of Formamidinium Lead Iodide Perovskite Nanocrystals

Formamidinium lead halide (FAPbX₃, X = Cl, Br, I) perovskite materials have recently drawn an increased amount of attention owing to their superior optoelectronic properties and enhanced material stability as compared with their methylammonium-based (MA-based) analogues. Herein, we report a study of the pressure-induced structural and optical evolutions of FAPbI₃ hybrid organic-inorganic perovskite nanocrystals (NCs) using a synchrotron-based X-ray scattering technique coupled to in situ absorption and photoluminescence spectroscopies. As a result of their unique structural stability and soft nature, FAPbI₃ NCs exhibit a wide range of band-gap tunability (1.44-2.17 eV) as a function of pressure (0-13.4 GPa). The study presented here not only provides an efficient and chemically orthogonal means to controllably engineer the band gap of FAPbI₃ NCs using pressure but more importantly sheds light on how to strategically design the band gaps of FA-based hybrid organic-inorganic perovskites for various optoelectronic applications.