Formamidinium iodide

Formamidinium lead iodide shows a narrower bandgap than the commonly used methylammonium lead iodide (1.48 eV compared to ~1.57 eV), and hence lies closer to that favourable for optimum solar conversion efficiencies. Spin-coating the formamidinium iodide (FAI) plus PbI2 precursor solution in N,N-dimethylformamide (DMF) initially resulted in discontinuous perovskite films. However, by adding a small amount of hydroiodic acid (HI) to the stoichiometric FAI, extremely uniform and continuous films were formed.
Controlled humidity is another deciding factor that affects the film morphology, crystallinity, and optical and electrical properties of FAPbI3 [2]. 16.6% PCE was achieved with low relative humidity of 2%, with the device efficiency dropped to about half (8.6%) when the humidity was 40%.
Low-volatility additives such as FACl and MACl are good candidates for assisting in the crystallisation of phase pure α-FAPbI3 via the formation of intermediate mixtures, which prohibits the crystallisation of the δ-FAPbI3 phase. It also has been observed that the black perovskite-type polymorph (α-phase), which is stable at relatively high temperatures (above 160 oC), turned into the yellow FAPbI3 polymorph (δ-phase) in an ambient humid atmosphere. Results show that incorporation of MAPbBr3 into FAPbI3 stabilises the perovskite phase of FAPbI3 and improves the power conversion efficiency of the solar cell to more than 18% under a standard illumination of 100 mW/cm2.
With an approach of FAPbI3 crystallisation by the direct intramolecular exchange of dimethylsulfoxide (DMSO) molecules intercalated in PbI2 with formamidinium iodide, device with performance over 20% has been fabricated.

Organohalide based perovskites have emerged as an important class of material for solar cell applications. Our perovskites precursors with extremely low water contents are useful for synthesizing mixed cation or anion perovskites needed for the optimization of the band gap, carrier diffusion length and power conversion efficiency of perovskites based solar cells.

Formamidinium iodide (FAI) is an organic halide, which can be used as a precursor solution in the fabrication of perovskite-based heterojunction solar cells.
With an approach of FAPbI3 crystallisation by the direct intramolecularexchange of dimethylsulfoxide (DMSO) molecules intercalated in PbI2 with formamidiniumiodide, device with performance over 20% has been fabricated [5].

Formamidinium lead iodide shows a narrower bandgap than the commonly used methylammonium leadiodide (1.48 eV compared to ~1.57 eV),and hence lies closer to that favourable for optimum solar conversion efficiencies. With an approach of FAPbI3 crystallisation by the direct intramolecularexchange of dimethylsulfoxide (DMSO) molecules intercalated in PbI2 with formamidiniumiodide, device with performance over 20% has been fabricated.

Formamidinium iodide is one of the most common precursors used in the preparation of perovskite-based opto-electronic systems, including light-emitting diodes (LEDs) and perovskite solar cells (PSCs).

[1] EPERON G E, STRANKS S D, MENELAOU C, et al. Formamidinium lead trihalide: a broadly tunable perovskite for efficient planar heterojunction solar cells†[J]. Energy & Environmental Science, 2014, 3: 982-988. DOI:10.1039/C3EE43822H.
[2] SARAH WOZNY. Controlled Humidity Study on the Formation of Higher Efficiency Formamidinium Lead Triiodide-Based Solar Cells[J]. Chemistry of Materials, 2015, 27 13: 4814-4820. DOI:10.1021/acs.chemmater.5b01691.
[3] ZAIWEI WANG. Additive-Modulated Evolution of HC(NH2)2PbI3 Black Polymorph for Mesoscopic Perovskite Solar Cells[J]. Chemistry of Materials, 2015, 27 20: 7149-7155. DOI:10.1021/acs.chemmater.5b03169.
[4] Compositional engineering of perovskite materials for high-performance solar cells, N. Jeon et al., Nature 517, 476–480 (2015), doi:10.1038/nature14133.
[5] WOON SEOK YANG. High-performance photovoltaic perovskite layers fabricated through intramolecular exchange[J]. Science, 2015, 348 6240. DOI:10.1126/science.aaa9272.
[6] Temperature dependence of hole conductor free formamidinium lead iodide perovskite based solar cells, S. Aharon et al., J. Mater. Chem. A., 3, 9171-9178 (2015), DOI: 10.1039/C4TA05149A. 
[7] High-Efficiency Perovskite Solar Cells Based on the Black Polymorph of HC(NH2)2PbI3, J-W. Lee et al., Adv. Mater., 26: 4991–4998 (2014). doi:10.1002/adma.201401137. 
[8] Efficient hole-conductor-free, fully printable mesoscopic perovskite solar cells with a broad light harvester NH2CH=NH2PbI3, M. Hu et al., J. Mater. Chem. A, 2, 17115-17121 (2014), DOI: 10.1039/C4TA03741C.