Low-bandgap mixed tin–lead iodide perovskites with reduced methylammonium for simultaneous enhancement of solar cell efficiency and stability


High-performance perovskite/perovskite tandem solar cells require high-efficiency and stable low-bandgap perovskite subcells. State-of-the-art low-bandgap mixed tin–lead iodide perovskite solar cells exhibit either a high power-conversion efficiency or improved stability, but not both. Here we report a two-step bilayer interdiffusion growth process to simultaneously meet both requirements for formamidinium-based low-bandgap mixed tin–lead iodide perovskite solar cells. The bilayer interdiffusion growth process allows for the formation of high-quality and large-grained perovskite films with only 10 mol% volatile methylammonium. Additionally, one-dimensional pyrrolidinium perovskite was applied to passivate the perovskite film and improve the junction quality, which resulted in a carrier lifetime of 1.1 μs and an open circuit voltage of 0.865 V for our perovskite film and device with a bandgap of 1.28 eV. Our strategies enabled a power-conversion efficiency of 20.4% for low-bandgap perovskite solar cells under AM 1.5G illumination. More importantly, an encapsulated device can retain 92% of its initial efficiency after 450 h of continuous 1 sun illumination.

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Fig. 1: Mixed Sn–Pb perovskite films prepared by the BIG process.
Fig. 2: Composition and degradation of mixed Sn–Pb perovskite films fabricated by the BIG process.
Fig. 3: 1D PySnxPb1–xI3 passivation of mixed Sn–Pb perovskite thin films.
Fig. 4: Single-junction and tandem PSCs.

Data availability

All data generated or analysed during this study are included in the published article and its Supplementary Information.


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This material is based on work supported by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Solar Energy Technologies Office Award no. DE-EE0008753. The TPD-MS study was supported by the National Science Foundation under contract no. DMR-1807818. K.K.S. and R.J.E. were supported by the US Air Force Research Laboratory under agreement no. FA9453-18-2-0037, and N.S., B.S., N.J.P. and R.J.E. were supported by the US Air Force Research Laboratory under agreement no. FA9453-19-C-1002. The US Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon.

Author information




C.L., Z.S. and Y.Y. conceived the project. C.L. carried out the single-junction low-bandgap cell and tandem cell fabrication. C.C. prepared the wide-bandgap cell and helped with the tandem cell fabrication. D.L. participated in the wide-bandgap cell fabrication. Z.S. conducted the TPD-MS measurements. C.X. and C.J. helped with the KPFM. B.S. conducted the PDS and SE measurement. S.P.H. conducted the TOF–SIMS measurement. N.S. and K.K.S. helped with the PL and TRPL measurements. L.C. and Y.L. participated in the characterization. Y.-W.K. helped with the 1H NMR measurements. C.L., Z.S. and Y.Y. analysed the data and wrote the manuscript. M.J.H., D.Z., RJ.E., N.J.P. and M.A.-J. helped with the manuscript preparation. All the authors discussed the results and commented on the manuscript. Y.Y. supervised the project.

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Correspondence to Zhaoning Song or Yanfa Yan.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–32 and Tables 1 and 2.

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Supplementary Data

Statistical source data for Supplementary Figs. 2 and 4, point data, error bars and PDS raw data for Supplementary Figs. 9 and 11b.

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Li, C., Song, Z., Chen, C. et al. Low-bandgap mixed tin–lead iodide perovskites with reduced methylammonium for simultaneous enhancement of solar cell efficiency and stability. Nat Energy 5, 768–776 (2020). https://doi.org/10.1038/s41560-020-00692-7

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