Design of low bandgap tin–lead halide perovskite solar cells to achieve thermal, atmospheric and operational stability

Abstract

Low bandgap tin–lead iodide perovskites are key components of all-perovskite tandem solar cells, but can be unstable because tin is prone to oxidation. Here, to avoid a reaction with the most popular hole contact, we eliminated polyethylenedioxythiophene:polystyrenesulfonate as a hole transport layer and instead used an upward band offset at an indium tin oxide–perovskite heterojunction to extract holes. To suppress oxidative degradation, we improved the morphology to create a compact and large-grained film. The tin content was kept at or below 50% and the device capped with a sputtered indium zinc oxide electrode. These advances resulted in a substantially improved thermal and environmental stability in a low bandgap perovskite solar cell without compromising the efficiency. The solar cells retained 95% of their initial efficiency after 1,000 h at 85 °C in air in the dark with no encapsulation and in a damp heat test (85 °C with 85% relative humidity) with encapsulation. The full initial efficiency was maintained under operation near the maximum power point and near 1 sun illumination for over 1,000 h.

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Fig. 1: Replacement of PEDOT:PSS with an ITO–perovskite heterojunction as the hole contact.
Fig. 2: Thermal and atmospheric stability of tin-lead perovskite solar cells.
Fig. 3: Morphology dependence of tin–lead perovskite oxidation.
Fig. 4: Normalized performance as a function of ageing time for FA0.75Cs0.25Sn0.4Pb0.6I3 solar cells.

Data availability

The data that support the plots within this article and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

This research was supported by the Office of Naval Research award N00014-17-1-2212 and by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under Solar Energy Technologies Office (SETO) agreement no. DE-EE0008551. Work at the Stanford Nano Shared Facilities (SNSF) was supported by the National Science Foundation award ECCS-1542152. S.P.D., M.F.A.M.v.H. and G.T. were supported by the US Department of Energy contract no. DE-AC36-08GO28308 with the Alliance for Sustainable Energy LLC, Manager and Operator of the National Renewable Energy Laboratory (NREL). The authors acknowledge support from the De-risking Halide Perovskite Solar Cells and Combined Characterization projects at NREL, funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technologies Office. J.J.B. was supported by the Office of Naval Research. We thank S. U. Nanayakkara for performing the atomic force microscopy measurements.

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Contributions

R.P. and T.L., under the supervision of M.D.M., designed the study. R.P. and T.L. designed the experiments, fabricated solar cells and conducted and interpreted various characterization. S.P.D. and G.T. conducted and interpreted all the XPS measurements. S.P.D., E.J.W., T.L., R.P., J.A.R., G.E.E., S.A.S., J.W., M.F.A.M.v.H., A.F.P. and C.C.B. fabricated devices and/or conducted various stability tests. C.d.P. performed the SEM characterization. R.P. wrote the first draft of the paper. M.D.M., J.J.B. and S.F.B. supervised the work. All the authors contributed to the analysis of the results and revision of the paper.

Corresponding author

Correspondence to Michael D. McGehee.

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Competing interests

T.L. and G.E.E. are co-founders of, and M.D.M. is an advisor to, Swift Solar Inc., a company commercializing perovskite solar cells. All other authors declare no competing interests.

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Supplementary Figs. 1–14, Note 1, Table 1 and ref. 1.

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Prasanna, R., Leijtens, T., Dunfield, S.P. et al. Design of low bandgap tin–lead halide perovskite solar cells to achieve thermal, atmospheric and operational stability. Nat Energy 4, 939–947 (2019). https://doi.org/10.1038/s41560-019-0471-6

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