# FAPbI₃ (formamidinium lead iodide): phases, band gap and solar cells

> FAPbI₃ explained: the black cubic α-phase and yellow hexagonal δ-phase, its 1.48 eV band gap, how mixed cations stabilise it and its role in solar cells.

URL: https://www.labcanvas.com/perovskites/fapbi3

Formamidinium lead iodide, HC(NH₂)₂PbI₃ (FAPbI₃), is a hybrid halide perovskite with formamidinium on the A site (Stoumpos et al. 2013); its black α-phase is cubic (Jeong et al. 2021). Its band gap of 1.48 eV is narrower than the 1.55 eV of methylammonium lead iodide (Zheng et al. 2022), and FAPbI₃-based cells passed 20% in 2015 (Yang et al. 2015). Pure FAPbI₃ can also crystallise as a yellow, hexagonal, non-perovskite δ-phase, so most high-efficiency cells stabilise the black phase by mixing in other cations or anions (Jeon et al. 2015; Saliba et al. 2016).

Perovskites Published 27 October 2026 Last updated 27 October 2026 9 references

![FAPbI₃: The black, narrow-gap formamidinium perovskite (HC(NH₂)₂PbI₃)](https://www.labcanvas.com/materials/fapbi3/fapbi3-cover.webp)

**Contents**

**Contents**

- FAPbI₃ at a glance
- FAPbI₃ structure drawing (high-resolution SVG)
- FAPbI₃ in 3D (interactive)
- FAPbI₃ structure explained
- Band gap: why FAPbI₃ matters for solar cells
- Stabilising the black phase: mixed cations and anions
- FAPbI₃ in high-efficiency perovskite solar cells
- How FAPbI₃ is made
- How to draw the FAPbI₃ structure
- FAPbI₃ compared with other lead halide perovskites
- Related materials
- More on LabCanvas
- Frequently asked questions
- References

## FAPbI₃ at a glance

| Formula | HC(NH₂)₂PbI₃ (FAPbI₃) (Stoumpos et al. 2013) |
| --- | --- |
| Molar mass | 632.98 g mol⁻¹ (calculated from the formula) |
| A-site cation | Formamidinium, HC(NH₂)₂⁺ (Stoumpos et al. 2013); ionic radius 2.79 Å vs 2.70 Å for methylammonium and 1.81 Å for Cs⁺ (as given by Saliba et al. 2016) |
| Black α-phase | Cubic, photoactive perovskite (Jeong et al. 2021; Saliba et al. 2016); obtained only at high temperature in pure FAPbI₃ (Zheng et al. 2022) |
| Yellow δ-phase | Photoinactive, non-perovskite, hexagonal (Saliba et al. 2016); the stable form at low temperature (Zheng et al. 2022) |
| Band gap | 1.48 eV, vs 1.55 eV for MAPbI₃ (Zheng et al. 2022); 1.48 eV measured for component-pure α-FAPbI₃ (Wang et al. 2023) |
| Absorption edge | About 840 nm (calculated from the 1.48 eV gap) |
| FAPbI₃ films | Dense (111)-oriented films by intramolecular exchange; FAPbI₃-based cells above 20% (Yang et al. 2015) |
| Stabilised by MAPbBr₃ | Mixing MAPbBr₃ into FAPbI₃ stabilises the perovskite phase; cells above 18% (Jeon et al. 2015) |
| Triple cation | Cs/MA/FA mixtures suppress the yellow phase; stabilised output of 21.1% (Saliba et al. 2016) |
| α-FAPbI₃ cells | 25.6% (certified 25.2%) with formate anion engineering (Jeong et al. 2021) |
| Key reports | Jeon et al., Nature 517, 476 (2015); Saliba et al., Energy Environ. Sci. 9, 1989 (2016); Jeong et al., Nature 592, 381 (2021) |

## FAPbI₃ structure drawing (high-resolution SVG)

![FAPbI₃ structure drawn as a LabCanvas Library object](https://www.labcanvas.com/materials/fapbi3/fapbi3-drawing.webp)

The cubic ABX₃ perovskite structure of black α-FAPbI₃ as a LabCanvas Library object: PbI₆ octahedra (grey Pb, red-brown I) sharing corners, with the formamidinium cation (green) in each cavity drawn as one sphere. A schematic; edit colours, cells and labels in the figure editor.

[Edit the drawing in LabCanvas](https://www.labcanvas.com/editor.html?add=perovskite)[Download SVG](https://www.labcanvas.com/materials/fapbi3/fapbi3-drawing.svg)[Download PNG (3000 px)](https://www.labcanvas.com/materials/fapbi3/fapbi3-drawing.png)

## FAPbI₃ in 3D (interactive)

![FAPbI₃ 3D model](https://www.labcanvas.com/gallery3d/halideperovskite3d.webp)

Loading the 3D model…

A lead halide perovskite in 3D: corner-sharing PbI₆ octahedra with the formamidinium cation drawn as one green sphere in each cavity, an idealised cubic schematic of the black α-phase. Drag to turn it.

[Open in the 3D Studio](https://www.labcanvas.com/studio3d.html?add=halideperovskite3d)

## FAPbI₃ structure explained

FAPbI₃ has the ABX₃ formula of a perovskite: A is the organic formamidinium cation, HC(NH₂)₂⁺, B is lead and X is iodide (Stoumpos et al. 2013). The **black α-phase** is the cubic perovskite (Jeong et al. 2021): corner-sharing PbI₆ octahedra with formamidinium in the cages. For the general picture of corner-sharing octahedra and the A-site cage, see the [perovskite structure](https://www.labcanvas.com/perovskites) hub.

Formamidinium (2.79 Å) is larger than methylammonium (2.70 Å) and much larger than caesium (1.81 Å) (radii as given by Saliba et al. 2016). That size is why pure FAPbI₃ does not always form a perovskite: it can instead crystallise as a **yellow δ-phase**, a photoinactive, hexagonal, non-perovskite structure, and the black α-phase is sensitive to solvents and humidity (Saliba et al. 2016). In pure FAPbI₃ the yellow non-perovskite phase is the stable one at low temperature and the black phase forms only at high temperature (Zheng et al. 2022).

## Band gap: why FAPbI₃ matters for solar cells

Replacing methylammonium with formamidinium narrows the band gap: FAPbI₃ has a gap of 1.48 eV against 1.55 eV for MAPbI₃ (Zheng et al. 2022), and component-pure α-FAPbI₃ films stabilised with a volatile ammonium acetate additive showed 1.48 eV and cells above 21% (Wang et al. 2023). The narrower gap extends absorption to about 840 nm (calculated from 1.48 eV). Yang et al. (2015) likewise note that the band gap of FAPbI₃ allows broader absorption of the solar spectrum than MAPbI₃, and Saliba et al. (2016) that it lies closer to the single-junction optimum.

## Stabilising the black phase: mixed cations and anions

- **FA/MA cations.** Mixing formamidinium and methylammonium on the A site extends the absorption onset further into the red and raised the short-circuit current over methylammonium-only cells (Pellet et al. 2014).
- **Adding MAPbBr₃.** Jeon et al. (2015) combined FAPbI₃ with MAPbBr₃; the bromide-containing mixture stabilised the perovskite phase of FAPbI₃ and gave cells above 18% under standard illumination.
- **Triple cation (Cs/MA/FA).** Saliba et al. (2016) added a small amount of caesium to FA/MA mixed-halide perovskites. The smaller Cs⁺ shifts the tolerance factor towards the cubic black phase, suppressing the yellow-phase impurities seen in Cs-free films; the films were more thermally stable, less sensitive to processing conditions, and reached a stabilised 21.1%, with about 18% after 250 hours under operation.
- **Anion engineering of α-FAPbI₃.** Jeong et al. (2021) used the pseudo-halide formate (HCOO⁻) to suppress anion-vacancy defects at grain boundaries and surfaces, reaching 25.6% (certified 25.2%).

## FAPbI₃ in high-efficiency perovskite solar cells

Perovskite solar cells began with methylammonium lead halides as sensitisers at 3.8% (Kojima et al. 2009). By 2016, the best perovskite cells used a mixture of formamidinium and methylammonium as the A-site cations (Saliba et al. 2016). Yang et al. (2015) deposited dense FAPbI₃ films by intramolecular exchange of DMSO intercalated in PbI₂ with formamidinium iodide, and their FAPbI₃-based cells exceeded 20%. Jeong et al. (2021) describe the cubic α-phase of FAPbI₃ as the most promising semiconductor for highly efficient and stable perovskite solar cells, and their formate-treated α-FAPbI₃ cells reached 25.6%.

## How FAPbI₃ is made

- **Single crystals and powders.** FAPbI₃ and related AMI₃ iodides have been prepared by several routes and their structures solved by single-crystal X-ray diffraction; their properties depend strongly on the preparation method (Stoumpos et al. 2013).
- **Intramolecular exchange.** Formamidinium iodide replaces DMSO intercalated in PbI₂, giving dense, large-grained (111)-oriented FAPbI₃ films without residual PbI₂ (Yang et al. 2015).

## How to draw the FAPbI₃ structure

For a paper, slide or poster, draw the black α-phase as one cubic cell: a PbI₆ octahedron at each corner sharing iodides with its neighbours, and the formamidinium ion in the central cage. A side-by-side panel of the yellow δ-phase (hexagonal, non-perovskite) explains why phase stability matters. In the LabCanvas figure editor, the Library’s Perovskite crystal object draws the ABX₃ cell with its corner-sharing octahedra, which you can recolour, repeat over several cells and export as a high-resolution SVG, and the LabCanvas 3D Studio has a perovskite model you can turn and export as an image; the [perovskite structure](https://www.labcanvas.com/perovskites) page shows the shared ABX₃ framework that FAPbI₃, MAPbI₃ and CsPbBr₃ all start from.

## FAPbI₃ compared with other lead halide perovskites

| Material | A cation (radius) | Band gap | Room-temperature phase issue | Source |
| --- | --- | --- | --- | --- |
| MAPbI₃ | Methylammonium (2.70 Å) | 1.55 eV | Structural phase transition at 55 °C; moisture sensitive | Zheng et al. 2022; Saliba et al. 2016 |
| FAPbI₃ | Formamidinium (2.79 Å) | 1.48 eV | Can form the yellow, hexagonal, non-perovskite δ-phase | Zheng et al. 2022; Saliba et al. 2016 |
| CsPbI₃ | Caesium (1.81 Å) | 1.73 eV (perovskite phase) | Orthorhombic yellow δ-phase at room temperature; black phase stable only above 300 °C | Saliba et al. 2016 |
| Cs/MA/FA triple cation | Mixture | Absorption and PL blue-shifted by ~10 nm vs the Cs-free mixture | Yellow phase suppressed; stabilised 21.1% cells | Saliba et al. 2016 |

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[![MAPbI₃: The hybrid perovskite behind perovskite solar cells (CH₃NH₃PbI₃)](https://www.labcanvas.com/materials/mapbi3/mapbi3-cover.webp) Perovskite CH₃NH₃PbI₃ MAPbI₃ MAPbI₃ (CH₃NH₃PbI₃): tetragonal and cubic phases, 1.5 eV band gap, the first perovskite solar cells, long diffusion lengths, instability and lead toxicity.](https://www.labcanvas.com/perovskites/mapbi3)

[![CsPbBr₃: All-inorganic perovskite with bright green emission (CsPbBr₃)](https://www.labcanvas.com/materials/cspbbr3/cspbbr3-cover.webp) Perovskite CsPbBr₃ CsPbBr₃ CsPbBr₃ and CsPbX₃ perovskite quantum dots: orthorhombic structure, hot-injection synthesis, emission tunable over 410–700 nm, anion exchange and uses.](https://www.labcanvas.com/perovskites/cspbbr3)

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## Frequently asked questions

### What is FAPbI₃?

Formamidinium lead iodide, HC(NH₂)₂PbI₃: a hybrid halide perovskite with formamidinium on the A site, lead on the B site and iodide on the X site. Its black α-phase is a cubic perovskite (Jeong et al. 2021) used as the light absorber in perovskite solar cells.

### What is the band gap of FAPbI₃?

About 1.48 eV, narrower than the 1.55 eV of MAPbI₃ (Zheng et al., Chem. Sci. 2022; Wang et al. 2023), so FAPbI₃ absorbs further into the near infrared (to about 840 nm, calculated from 1.48 eV).

### What is the difference between α-FAPbI₃ and δ-FAPbI₃?

α-FAPbI₃ is the black, photoactive perovskite phase built from corner-sharing PbI₆ octahedra; δ-FAPbI₃ is a yellow, photoinactive, hexagonal non-perovskite phase. Pure FAPbI₃ can crystallise into either, and the black phase is sensitive to solvents and humidity (Saliba et al. 2016).

### Why does FAPbI₃ turn yellow?

Because it converts to, or crystallises as, the hexagonal δ-phase, which is photoinactive and not a perovskite, unlike the black α-phase. The black phase is sensitive to solvents and humidity (Saliba et al. 2016).

### How is the black phase of FAPbI₃ stabilised?

By mixing in other ions: methylammonium and bromide (MAPbBr₃; Jeon et al., Nature 2015), a small amount of caesium in a Cs/MA/FA triple cation (Saliba et al. 2016), or by treating α-FAPbI₃ films with additives such as formate, which suppresses anion-vacancy defects (Jeong et al. 2021).

### Is FAPbI₃ better than MAPbI₃ for solar cells?

Its narrower band gap (1.48 eV) lets it harvest more of the solar spectrum than MAPbI₃ (Zheng et al. 2022; Yang et al. 2015), and α-FAPbI₃ cells have reached 25.6% (Jeong et al. 2021). Its drawback is phase stability: it needs stabilising against the yellow δ-phase.

### What is a triple cation perovskite?

A lead mixed-halide perovskite with three A-site cations: caesium, methylammonium and formamidinium. Saliba et al. (2016) showed that adding Cs suppresses the yellow phase of FA perovskite, improves thermal stability and reproducibility, and gave a stabilised 21.1%.

### What is the crystal structure of FAPbI₃?

The black α-phase is a cubic perovskite of corner-sharing PbI₆ octahedra with formamidinium in the cages (Jeong et al. 2021). The yellow δ-phase is hexagonal and not a perovskite (Saliba et al. 2016).

## References

- Z. Zheng, S. Wang, Y. Hu, Y. Rong, A. Mei, H. Han. Development of formamidinium lead iodide-based perovskite solar cells: efficiency and stability. *Chem. Sci.* 2022, 13, 2167–2183. [doi:10.1039/D1SC04769H](https://doi.org/10.1039/D1SC04769H)
- D. Wang et al.. Stabilization of component-pure α-FAPbI₃ via volatile additives for stable photovoltaics. *ACS Appl. Mater. Interfaces* 2023, 15, 16818–16827. [doi:10.1021/acsami.3c01973](https://doi.org/10.1021/acsami.3c01973)
- C. C. Stoumpos, C. D. Malliakas, M. G. Kanatzidis. Semiconducting tin and lead iodide perovskites with organic cations: phase transitions, high mobilities, and near-infrared photoluminescent properties. *Inorg. Chem.* 2013, 52, 9019–9038. [doi:10.1021/ic401215x](https://doi.org/10.1021/ic401215x)
- N. J. Jeon, J. H. Noh, W. S. Yang, Y. C. Kim, S. Ryu, J. Seo, S. I. Seok. Compositional engineering of perovskite materials for high-performance solar cells. *Nature* 2015, 517, 476–480. [doi:10.1038/nature14133](https://doi.org/10.1038/nature14133)
- M. Saliba et al.. Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency. *Energy Environ. Sci.* 2016, 9, 1989–1997. [doi:10.1039/C5EE03874J](https://doi.org/10.1039/C5EE03874J)
- N. Pellet, P. Gao, G. Gregori, T.-Y. Yang, M. K. Nazeeruddin, J. Maier, M. Grätzel. Mixed-organic-cation perovskite photovoltaics for enhanced solar-light harvesting. *Angew. Chem. Int. Ed.* 2014, 53, 3151–3157. [doi:10.1002/anie.201309361](https://doi.org/10.1002/anie.201309361)
- W. S. Yang, J. H. Noh, N. J. Jeon, Y. C. Kim, S. Ryu, J. Seo, S. I. Seok. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange. *Science* 2015, 348, 1234–1237. [doi:10.1126/science.aaa9272](https://doi.org/10.1126/science.aaa9272)
- J. Jeong et al.. Pseudo-halide anion engineering for α-FAPbI₃ perovskite solar cells. *Nature* 2021, 592, 381–385. [doi:10.1038/s41586-021-03406-5](https://doi.org/10.1038/s41586-021-03406-5)
- A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. *J. Am. Chem. Soc.* 2009, 131, 6050–6051. [doi:10.1021/ja809598r](https://doi.org/10.1021/ja809598r)

## Draw FAPbI₃ for your paper or slides

LabCanvas is a browser workspace for scientific figures: framework clusters, linkers and nets, crystal structures in 2D and 3D, graphs and posters, all editable.

[Draw FAPbI₃ in LabCanvas](https://www.labcanvas.com/editor.html?add=perovskite)

**Contents**

- FAPbI₃ at a glance
- FAPbI₃ structure drawing (high-resolution SVG)
- FAPbI₃ in 3D (interactive)
- FAPbI₃ structure explained
- Band gap: why FAPbI₃ matters for solar cells
- Stabilising the black phase: mixed cations and anions
- FAPbI₃ in high-efficiency perovskite solar cells
- How FAPbI₃ is made
- How to draw the FAPbI₃ structure
- FAPbI₃ compared with other lead halide perovskites
- Related materials
- More on LabCanvas
- Frequently asked questions
- References