Cubic Perovskite Structure of Black Formamidinium Lead Iodide, α‑[HC(NH2)2]PbI3, at 298 K

ABSTRACT: The structure of black formamidinium lead halide, α-[HC(NH2)2]PbI3, at 298 K has been refined from high resolution neutron powder diffraction data and found to adopt a cubic perovskite unit cell, a = 6.3620(8) Å. The trigonal planar [HC(NH2)2] + cations lie in the central mirror plane of the unit cell with the formamidinium cations disordered over 12 possible sites arranged so that the C−H bond is directed into a cube face, whereas the −NH2 groups hydrogen bond (NH···I = 2.75−3.00 Å) with the iodide atoms of the [PbI3] − framework. High atomic displacement parameters for the formamidinium cation are consistent with rapid molecular rotations at room temperature as evidenced in ab initio molecular dynamic simulations. Hybrid halide perovskite solar cells have capturedsignificant research attention due to the demonstration of their use in highly efficient photovoltaic devices produced via low-cost deposition methods.1−7 The complete structure and dynamics of the systems, covering the inorganic framework, the molecular cation and their mutual interactions, all impact upo