Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Pseudo-halide anion engineering for α-FAPbI3 perovskite solar cells

This article has been updated


Metal halide perovskites of the general formula ABX3—where A is a monovalent cation such as caesium, methylammonium or formamidinium; B is divalent lead, tin or germanium; and X is a halide anion—have shown great potential as light harvesters for thin-film photovoltaics1,2,3,4,5. Among a large number of compositions investigated, the cubic α-phase of formamidinium lead triiodide (FAPbI3) has emerged as the most promising semiconductor for highly efficient and stable perovskite solar cells6,7,8,9, and maximizing the performance of this material in such devices is of vital importance for the perovskite research community. Here we introduce an anion engineering concept that uses the pseudo-halide anion formate (HCOO) to suppress anion-vacancy defects that are present at grain boundaries and at the surface of the perovskite films and to augment the crystallinity of the films. The resulting solar cell devices attain a power conversion efficiency of 25.6 per cent (certified 25.2 per cent), have long-term operational stability (450 hours) and show intense electroluminescence with external quantum efficiencies of more than 10 per cent. Our findings provide a direct route to eliminate the most abundant and deleterious lattice defects present in metal halide perovskites, providing a facile access to solution-processable films with improved optoelectronic performance.

Your institute does not have access to this article

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: Characterization of the FAPbI3 films.
Fig. 2: Solid-state NMR spectra and molecular dynamics simulations.
Fig. 3: Characterization of the photovoltaic performance of the FAPbI3 PSCs.
Fig. 4: Stability of the FAPbI3 PSCs.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Code availability

The code used for this study is available from the corresponding author upon reasonable request.

Change history

  • 08 April 2021

    This Article was amended to correct the Peer review information.


  1. Kojima, A., Teshima, K., Shirai, Y. & Miyasaka, T. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J. Am. Chem. Soc. 131, 6050–6051 (2009).

    Article  CAS  Google Scholar 

  2. Grätzel, M. The light and shade of perovskite solar cells. Nat. Mater. 13, 838–842 (2014).

    ADS  Article  CAS  Google Scholar 

  3. Park, N.-G. et al. Towards stable and commercially available perovskite solar cells. Nat. Energy 1, 16152 (2016).

    ADS  Article  CAS  Google Scholar 

  4. Correa-Baena, J. P. et al. Promises and challenges of perovskite solar cells. Science 358, 739–744 (2017).

    ADS  Article  CAS  Google Scholar 

  5. Lu, H., Krishna, A., Zakeeruddin, S. M., Grätzel, M. & Hagfeldt, A. Compositional and interface engineering of organic-inorganic lead halide perovskite solar cells. iScience 23, 101359 (2020).

    ADS  Article  CAS  Google Scholar 

  6. Eperon, G. E. et al. Formamidinium lead trihalide: a broadly tunable perovskite for efficient planar heterojunction solar cells. Energy Environ. Sci. 7, 982–988 (2014).

    Article  CAS  Google Scholar 

  7. Pellet, N. et al. Mixed-organic-cation perovskite photovoltaics for enhanced solar-light harvesting. Angew. Chem. Int. Ed. 53, 3151–3157 (2014).

    Article  CAS  Google Scholar 

  8. Jeon, N. J. et al. Compositional engineering of perovskite materials for high-performance solar cells. Nature 517, 476–480 (2015).

    ADS  Article  CAS  Google Scholar 

  9. Lu, H. et al. Vapor-assisted deposition of highly efficient, stable black-phase FAPbI3 perovskite solar cells. Science 370, eabb8985 (2020).

    Article  CAS  Google Scholar 

  10. De Wolf, S. et al. Organometallic halide perovskites: sharp optical absorption edge and its relation to photovoltaic performance. J. Phys. Chem. Lett. 5, 1035–1039 (2014).

    Article  CAS  Google Scholar 

  11. Stranks, S. D. et al. Electron-hole diffusion lengths exceeding 1 micrometer in an organometal trihalide perovskite absorber. Science 342, 341–344 (2013).

    ADS  Article  CAS  Google Scholar 

  12. Herz, L. M. et al. Charge-carrier mobilities in metal halide perovskites: fundamental mechanisms and limits. ACS Energy Lett. 2, 1539–1548 (2017).

    Article  CAS  Google Scholar 

  13. NREL. Best Research-Cell Efficiency Chart (accessed 17 March 2021).

  14. Zheng, X. et al. Managing grains and interfaces via ligand anchoring enables 22.3%-efficiency inverted perovskite solar cells. Nat. Energy 5, 131–140 (2020).

    ADS  Article  CAS  Google Scholar 

  15. Liu, Z. et al. A holistic approach to interface stabilization for efficient perovskite solar modules with over 2,000-hour operational stability. Nat. Energy 5, 596–604 (2020).

    ADS  Article  CAS  Google Scholar 

  16. Saliba, M. et al. Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency. Energy Environ. Sci. 9, 1989–1997 (2016).

    Article  CAS  Google Scholar 

  17. Kim, M. et al. Methylammonium chloride induces intermediate phase stabilization for efficient perovskite solar cells. Joule 3, 2179–2192 (2019).

    Article  CAS  Google Scholar 

  18. Min, H. et al. Efficient, stable solar cells by using inherent bandgap of α-phase formamidinium lead iodide. Science 366, 749–753 (2019).

    ADS  Article  CAS  Google Scholar 

  19. Yang, S. et al. Thiocyanate assisted performance enhancement of formamidinium based planar perovskite solar cells through a single one-step solution process. J. Mater. Chem. A 4, 9430–9436 (2016).

    Article  CAS  Google Scholar 

  20. Kim, D. H. et al. Bimolecular additives improve wide-band-gap perovskites for efficient tandem solar cells with CIGS. Joule 3, 1734–1745 (2019).

    Article  CAS  Google Scholar 

  21. Kim, D. et al. Efficient, stable silicon tandem cells enabled by anion-engineered wide-bandgap perovskites. Science 368, 155–160 (2020).

    ADS  Article  CAS  Google Scholar 

  22. Walker, B., Kim, G. H. & Kim, J. Y. Pseudohalides in lead-based perovskite semiconductors. Adv. Mater. 31, 1807029 (2019).

    Article  CAS  Google Scholar 

  23. Moore, D. T. et al. Direct crystallization route to methylammonium lead iodide perovskite from an ionic liquid. Chem. Mater. 27, 3197–3199 (2015).

    ADS  Article  CAS  Google Scholar 

  24. Seo, J. et al. Ionic liquid control crystal growth to enhance planar perovskite solar cells efficiency. Adv. Energy Mater. 6, 1600767 (2016).

    Article  CAS  Google Scholar 

  25. Nayak, P. K. et al. Mechanism for rapid growth of organic–inorganic halide perovskite crystals. Nat. Commun. 7, 13303 (2016).

    ADS  Article  CAS  Google Scholar 

  26. Meng, L. et al. Improved perovskite solar cell efficiency by tuning the colloidal size and free ion concentration in precursor solution using formic acid additive. J. Energy Chem. 41, 43–51 (2020).

    Article  Google Scholar 

  27. Khan, Y. et al. Waterproof perovskites: high fluorescence quantum yield and stability from a methylammonium lead bromide/formate mixture in water. J. Mater. Chem. C 8, 5873–5881 (2020).

    Article  CAS  Google Scholar 

  28. Askar, A. M. et al. Composition-tunable formamidinium lead mixed halide perovskites via solvent-free mechanochemical synthesis: decoding the Pb environments using solid-state NMR spectroscopy. J. Phys. Chem. Lett. 9, 2671–2677 (2018).

    Article  CAS  Google Scholar 

  29. Kubicki, D. J. et al. Cation dynamics in mixed-cation (MA)x(FA)1−xPbI3 hybrid perovskites from solid-state NMR. J. Am. Chem. Soc. 139, 10055–10061 (2017).

    Article  CAS  Google Scholar 

  30. Zhou, Z. et al. Synthesis, microwave spectra, X-ray structure, and high-level theoretical calculations for formamidinium formate. J. Chem. Phys. 150, 094305 (2019).

    ADS  Article  CAS  Google Scholar 

  31. Ross, R. et al. Some thermodynamics of photochemical systems. J. Chem. Phys. 46, 4590–4593 (1967).

    ADS  Article  CAS  Google Scholar 

  32. Tress, W. et al. Predicting the open-circuit voltage of CH3NH3PbI3 perovskite solar cells using electroluminescence and photovoltaic quantum efficiency spectra: the role of radiative and non-radiative recombination. Adv. Energy Mater. 5, 1400812 (2015).

    Article  CAS  Google Scholar 

  33. Jiang, Q. et al. Surface passivation of perovskite film for efficient solar cells. Nat. Photonics 13, 460–466 (2019).

    ADS  Article  CAS  Google Scholar 

  34. Yang, D. et al. Surface optimization to eliminate hysteresis for record efficiency planar perovskite solar cells. Energy Environ. Sci. 9, 3071–3078 (2016).

    Article  CAS  Google Scholar 

  35. Kuik, M., Koster, L. J., Wetzelaer, G. A. & Blom, P. W. Trap-assisted recombination in disordered organic semiconductors. Phys. Rev. Lett. 107, 256805 (2011).

    ADS  Article  CAS  Google Scholar 

  36. Green, M. Accuracy of analytical expressions for solar cell fill factors. Solar Cells 7, 337–340 (1982).

    ADS  Article  CAS  Google Scholar 

  37. Wang, Y. et al. Stabilizing heterostructures of soft perovskite semiconductors. Science 365, 687–691 (2019).

    ADS  Article  CAS  Google Scholar 

Download references


We thank W. R. Tress for discussions, and the staff at beamlines BL17B1, BL14B1, BL11B, BL08U and BL01B1 of the SSRF for providing the beamline, and the Swiss National Supercomputing Centre (CSCS) and EPFL computing center (SCITAS) for their support. This research was supported by the Technology Development Program to Solve Climate Changes of the National Research Foundation (NRF) funded by the Ministry of Science, ICT & Future Planning (2020M1A2A2080746). This work was also supported by ‘The Research Project Funded by U-K Brand’ (1.200030.01) of Ulsan National Institute of Science & Technology (UNIST). D.S.K. acknowledges the Development Program of the Korea Institute of Energy Research (KIER) (C0-2401 and C0-2402). L.E. acknowledges support from the Swiss National Science Foundation, grant number 200020_178860. U.R. acknowledges funding from the Swiss National Science Foundation via individual grant number 200020_185092 and the NCCR MUST. A.H. acknowledges the Swiss National Science Foundation, project ‘Fundamental studies of dye-sensitized and perovskite solar cells’, project number 200020_185041. M.G. acknowledges financial support from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 881603, and the King Abdulaziz City for Science and Technology (KACST).

Author information

Authors and Affiliations



J.J., B.W. and J.Y.K. conceived the project. J.J., Minjin Kim and H.L. prepared the samples, performed the relevant photovoltaic measurements, analysed the data and wrote the manuscript. J.S. synthesised the FAHCOO material. Minjin Kim and D.S.K. certified the efficiency of the PSCs. Y.J.Y. carried out photoluminescence and UV–vis absorption spectroscopy. S.J.C. and I.W.C. performed the time-resolved photoluminescence, SEM and XRD measurements. Y.J. and H.L. collected the light-intensity-dependent JV data. P.A. and U.R. designed and performed all the DFT calculations and molecular dynamics simulations. Maengsuk Kim and J.H.L contributed to the DFT calculations. A.M., M.A.H. and L.E. conducted the solid-state NMR measurements and analysis. B.P.D. performed the atomic force microscopy measurements. H.L. conducted the long-term operational stability measurements, EQEEL measurements and analysed the data. Y.Y. performed the two-dimensional grazing-incidence XRD measurements. F.T.E contributed to the analysis of the time-resolved photoluminescence data. S.M.Z. coordinated the project. A.H. and M.G. proposed experiments and M.G. wrote the final version of the manuscript. A.H., D.S.K., M.G. and J.Y.K. directed the work. All authors analysed the data and contributed to the discussions.

Corresponding authors

Correspondence to Anders Hagfeldt, Dong Suk Kim, Michael Grätzel or Jin Young Kim.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks the anonymous reviewers for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Characterization of the perovskite films with and without FAFo.

a, The Tauc plot of the 2% Fo-FAPbI3 perovskite film. b, A full photoluminescence decay of the reference, 2% Fo-FAPbI3 and 4% Fo-FAPbI3 perovskite films. c, The distribution of the grain sizes of the reference and 2% Fo-FAPbI3 films. The box + whisker plots show the distribution of the grain sizes for both reference and 2% Fo-FAPbI3 perovskite films. The distribution is based on 22 data points each. d, e, The top-view SEM image (d) and the cross-sectional SEM image (e) of the 4% Fo-FAPbI3 perovskite film. f, g, AFM images of the reference (f) and the 2% Fo-FAPbI3 (g) perovskite films. h, The XRD patterns of the reference, 2% Fo-FAPbI3 and 4% Fo-FAPbI3 perovskite films. Peaks labelled with an asterisk are assigned to the FTO substrates, which can be seen for the 4% sample owing to the lower intensity of the perovskite reflections. i, Integrated one-dimensional grazing-incidence XRD pattern of the reference and 2% Fo-FAPbI3 films.

Extended Data Fig. 2 The composition of the Fo-FAPbI3 perovskite film.

a, b, 1H–13C cross-polarization spectra of mechanosynthesized FAPbI3 with 5% FAHCOO (a) and a scraped thin film of 2% Fo-FAPbI3 (b), recorded at 12 kHz MAS and 100 K. In b the formate signal can be seen as a minor shoulder on the FAPbI3 peak. A minor signal arising from the PTFE that is used to seal the rotor is also visible. c, d, TOF-SIMS measurements of the reference (c) and the 2% Fo-FAPbI3 (d) films. e, Quantitative, directly detected 13C solid-state NMR measurement of 2% Fo-FAPbI3 scraped thin film at 12 kHz MAS and 100 K.

Extended Data Fig. 3 Ab initio molecular dynamics simulations.

a, Molecular dynamics snapshot showing the coordination of Pb2+ ions with HCOO anions in the perovskite precursor solution. As a guide to the eye, we highlight only Pb2+ and HCOO ions; the remaining ions and solvent molecules are shown as transparent. b, The radial distribution function g(r) between the oxygen atoms of HCOO and Pb2+ over the full ab initio molecular dynamics trajectory of around 11 ps. c, Initial configuration of FAPbI3 with surface iodide replaced by HCOO anions. d, The top view of surface atoms on the FA+-terminated side. e, The top view of the surface atoms on the Pb2+-terminated side. Pb2+–HCOO and FA+–HCOO bonding and hydrogen-bonding networks are illustrated with magenta dashed lines. All ions are shown in ball-and-stick representation. Pb2+ ions, yellow; iodide, light pink; oxygen, red; carbon, light blue; nitrogen, dark blue; sulfur, light yellow; hydrogen, white.

Extended Data Fig. 4 DFT-relaxed slabs of FAPbI3 with different anions adsorbed at an iodide-vacancy site on the surface.

a, Structure of a pure FAPbI3 slab with a Pb–I terminated surface on the top and an FA–I terminated surface on the bottom side. be, Front view of the Cl (b), Br (c), BF4 (d) and HCOO (e) passivated surface. f, An illustration of iodide-vacancy passivation by HCOO. g, h, DFT-relaxed FAPbI3 slab with HCOO adsorbed at the iodide-vacancy site on the Pb–I (g) and the FA–I (h) terminated surface. All chemical species are shown in ball-and-stick representation. Pb2+, grey; iodide, violet; oxygen, red; carbon, dark brown; nitrogen, light blue; bromide, red-brown; chloride, light green; boron atoms, dark green; fluoride, yellow; hydrogen atoms, white.

Extended Data Fig. 5 Bonding between formamidinium and different anions on the surface of FAPbI3.

a, Structure of a pure FAPbI3 slab with FA–I termination on the top and Pb–I termination on the bottom side. b, c, The front view (b) and the side view (c) of the HCOO passivated surface. df, Cl (d), Br (e) and BF4 (f) passivated surface. All chemical species are shown in ball-and-stick representation. Pb2+, grey; iodide, violet; oxygen, red; carbon, dark brown; nitrogen, light blue; bromide, red-brown; chloride, light green; boron atoms, dark green; fluoride, yellow; hydrogen, white. g, Relative desorption strength of FA+ cations on different passivated surfaces.

Extended Data Fig. 6 Photovoltaic performance of the PSCs under different conditions.

a, J–V curve of the target PSC measured without a metal mask. b, J–V curves of the reference PSC and the PSC with 2% formamidinium acetate. c, J–V curves of the reference and 2% Fo-FAPbI3 PSCs without the MACl additive. d, J–V curves of the reference and the 2% Fo-FAPbI3 PSCs without using octylammonium iodide passivation. FF, fill factor.

Extended Data Fig. 7 J–V metrics of the reference and target PSCs during the operational stability test.

ac, The change in Jsc (a), Voc (b) and fill factor (c) of the reference and target cells over the 450-h MPP tracking measurement.

Extended Data Table 1 Detailed J–V parameters of the reference and target PSCs under both reverse and forward voltage scans
Extended Data Table 2 Detailed J–V parameters of the reference and target PSCs under different light intensities

Supplementary information

Supplementary Information

This file contains Supplementary Notes 1-6, Supplementary Figs 1-3 and Supplementary References.

Video 1

The coordination of HCOO- anions with Pb2+cations.

Video 2

MD of HCOO- passivated FA-I terminated interface of FAPbI3.

Video 3

MD of HCOO- passivated Pb-I terminated interface of FAPbI3.

Video 4

Perovskite fabrication process.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Jeong, J., Kim, M., Seo, J. et al. Pseudo-halide anion engineering for α-FAPbI3 perovskite solar cells. Nature 592, 381–385 (2021).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing