Research Article: Formamidinium iodide: crystal structure and phase transitions

Date Published: April 01, 2017

Publisher: International Union of Crystallography

Author(s): Andrey A. Petrov, Eugene A. Goodilin, Alexey B. Tarasov, Vladimir A. Lazarenko, Pavel V. Dorovatovskii, Victor N. Khrustalev.

http://doi.org/10.1107/S205698901700425X

Abstract

Crystal structure, thermal behaviour and phase transitions of formamidinium iodide were studied by DTG, DSC, powder diffraction and X-ray crystallography.

Partial Text

Compounds with the general formula ABX3 [where A denotes an organic cation e.g. methylammonium (MA, CH3NH3+) or formamidinium [FA = CH(NH2)2, CH3NH3]; B = Pb, Sn; X = I, Br, Cl] belong to a class of hybrid organic–inorganic perovskites and perform as outstanding light harvesters. These compounds gave birth to a new field of photovoltaics – perovskite solar cells – when Kojima and co-authors used (MA)PbI3 as a light sensitizer for the first time in dye-sensitized solar cells (DSSCs) in 2009 and showed 3.8% efficiency (Kojima et al., 2009 ▸). Since then, a revolutionary breakthrough has occured in this area and the highest efficiency now has reached 22.1%.

At a temperature of 100 K, compound I crystallizes in the monoclinic space group P21/c. The formamidinium cation adopts a planar symmetrical structure [r.m.s. deviation is 0.002 Å, and the C—N bond lengths are 1.301 (7) and 1.309 (8) Å; Fig. 1 ▸]. The iodide anion does not lie within the cation plane, but deviates from it by 0.643 (10) Å. The cation and anion in I form a tight ionic pair by the strong N1—H1A⋯I1 hydrogen bond (Table 1 ▸ and Fig. 1 ▸).

In the crystal of I, the tight ionic pairs form hydrogen-bonded zigzag-like chains propagating toward [20] by the strong inter­molecular N2—H2A⋯I1i hydrogen bonds (Table 1 ▸ and Fig. 4 ▸). The hydrogen-bonded chains are further packed in stacks along [100] (Fig. 4 ▸) [symmetry code: (i) x − 1, −y + , z + ].

Polycrystalline powder of I was purchased from Dyesol and used without further purification. Single crystals suitable for X-ray structural study were obtained by recrystallization from an anhydrous ethanol solution by slow cooling.

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. X-ray diffraction study of I was carried out on the ‘Belok’ beamline of the National Research Center ‘Kurchatov Institute’ (Moscow, Russian Federation) using a Rayonix SX165 CCD detector. Reflection intensities measured were corrected for absorption using the Scala (Evans, 2006 ▸) program.

 

Source:

http://doi.org/10.1107/S205698901700425X