Formamidine hydriodide
[CAS# 879643-71-7]

Identification

• Classification: Chemical reagent >> Organic reagent >> Imine, amidine
• Name: Formamidine hydriodide
• Synonyms: Methanimidamide hydroiodide
• Molecular Formula: CH₄N₂^.HI
• Molecular Weight: 171.97
• CAS Registry Number: 879643-71-7
• EC Number: 827-106-7
• SMILES: C(=N)N.I

Properties

• Melting point: 335 ºC (Expl.)
• Boiling point: 127.9 ºC 760 mmHg (Calc.)^*
• Flash point: 31.1 ºC (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07 Warning
• Hazard Statements: H302-H315-H319-H335
• Precautionary Statements: P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335

Discovory and Applicatios

Formamidine hydriodide (FAI, CH(NH₂)₂HI) is a salt consisting of the protonated formamidine cation and iodide anion. It has become particularly important in recent decades due to its role in the development of hybrid organic–inorganic perovskite materials for optoelectronic applications.

The substance was originally investigated as a simple organic iodide salt, but its major impact emerged with the rise of perovskite solar cell research. When combined with lead iodide (PbI₂), formamidine hydriodide forms formamidinium lead iodide (FAPbI₃), a perovskite semiconductor with a favorable band gap (\~1.48 eV) for photovoltaic applications. This material has been shown to absorb visible light more efficiently than the widely used methylammonium lead iodide (MAPbI₃), while also offering improved thermal stability.

The discovery of FAI-based perovskites addressed some of the limitations associated with methylammonium-based systems, particularly their instability under heat and moisture. Perovskites derived from FAI have demonstrated better structural stability, reduced phase degradation, and enhanced power conversion efficiency in solar cells. As a result, formamidine hydriodide has become a critical precursor for the preparation of high-performance perovskite absorbers.

Beyond its role in photovoltaics, FAI has also been studied in light-emitting diodes (LEDs) and photodetectors. In perovskite LEDs, the incorporation of FAI into the active layer improves crystallinity and reduces non-radiative recombination, enhancing brightness and operational lifetime. Similarly, in photodetectors, FAI-derived perovskites contribute to high responsivity and fast photoresponse times.

From a chemical perspective, FAI is typically synthesized by neutralizing formamidine acetate with hydroiodic acid under controlled conditions, followed by purification to remove residual water and impurities. The resulting crystalline salt is highly soluble in polar solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), which facilitates its use in solution-processing techniques commonly employed in thin-film device fabrication.

Applications of formamidine hydriodide have expanded through the engineering of mixed-cation perovskites. By partially substituting formamidinium with other cations, such as cesium or methylammonium, researchers have created perovskite films with improved phase stability and higher device performance. FAI thus plays a central role not only as a single-cation source but also as a key component in multi-cation perovskite formulations.

The significance of FAI lies in its contribution to advancing perovskite solar cell efficiency, which has rapidly increased from less than 5% in the early 2010s to over 25% in recent years. Its stability advantage and favorable band gap have made it a preferred choice for research aimed at commercializing perovskite-based photovoltaics. Continued study of FAI and its derivatives is expected to further refine device performance and stability, supporting the transition of perovskite technologies from laboratory research to practical applications.

In conclusion, formamidine hydriodide is a relatively simple organic salt whose importance arises from its ability to form high-quality perovskite absorbers with superior optoelectronic properties. Its discovery as a perovskite precursor has enabled significant progress in solar cells, LEDs, and photodetectors, making it a cornerstone material in modern optoelectronic research.

References

2025. Unveiling and optimizing the role of ALD-SnO2 in Perovskite solar cells. Advances in Industrial and Engineering Chemistry.
DOI: 10.1007/s44405-025-00010-3

2025. Facile solid state synthesis of lead free FA3Bi2I9 perovskite and extensive analysis of optoelectronic properties at room temperature. Optical and Quantum Electronics.
DOI: 10.1007/s11082-025-08100-8

2025. Operando spin observation elucidating performance-improvement mechanisms during operation of Ruddlesden�Popper Sn-based perovskite solar cells. npj Flexible Electronics.
DOI: 10.1038/s41528-024-00376-2