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Cation and anion immobilization through chemical bonding enhancement with fluorides for stable halide perovskite solar cells


Defects play an important role in the degradation processes of hybrid halide perovskite absorbers, impeding their application for solar cells. Among all defects, halide anion and organic cation vacancies are ubiquitous, promoting ion diffusion and leading to thin-film decomposition at surfaces and grain boundaries. Here, we employ fluoride to simultaneously passivate both anion and cation vacancies, by taking advantage of the extremely high electronegativity of fluoride. We obtain a power conversion efficiency of 21.46% (and a certified 21.3%-efficient cell) in a device based on the caesium, methylammonium (MA) and formamidinium (FA) triple-cation perovskite (Cs0.05FA0.54MA0.41)Pb(I0.98Br0.02)3 treated with sodium fluoride. The device retains 90% of its original power conversion efficiency after 1,000 h of operation at the maximum power point. With the help of first-principles density functional theory calculations, we argue that the fluoride ions suppress the formation of halide anion and organic cation vacancies, through a unique strengthening of the chemical bonds with the surrounding lead and organic cations.

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This work is supported by the National Natural Science Foundation of China (51722201; 51672008; 91733301), National Key Research and Development Program of China grant no. 2017YFA0206701, the Natural Science Foundation of Beijing, China (grant no. 4182026), the Young Talent Thousand Program, National Key Research and Development Program of China grant no. 2016YFB0700700, the National Natural Science Foundation of China (51673025) and Beijing Municipal Science and Technology Project no. Z181100005118002. S.T. acknowledges funding from the Computational Sciences for Energy Research tenure track programme of Shell, NWO and FOM (project no. 15CST04-2). The authors would like to thank W. Zou and J. Wang (Nanjing Tech University) for the PLQE measurement during the revision process, and Z. Dai for providing the dynamic light scattering measurement.

Author information

H.Z. and N.L. conceived the idea and designed the experiments. S.T. designed and performed the DFT calculations. Both N.L. and X.N. were involved in all of the experimental parts. Y.C., Z.X., L.W. and H.L. contributed to the fabrication of high-performance PSCs. Z.Q., Y.Z. and L.L. helped to modify the experiments. Y.Lun, X.W. and J.H. performed the KPFM measurements, while Y.Liu, H.X. and Y.G. carried out the UPS and XPS measurement. G.Z. provided the film microstructure analysis. G.B. and C.K.O. assisted in DFT calculations. C.H., Y.B. and S.Y. performed ToF-SIMS measurements. H.Z., Q.C., S.T. and N.L. wrote the manuscript. C.K.O., X.N. and G.B. revised the manuscript. All authors were involved in the discussion of data analysis and commented on the manuscript. N.L. and S.T. have contributed equally to this work.

Competing interests

The authors declare no competing interests.

Correspondence to Huanping Zhou.

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Fig. 1: The characterization of perovskite thin films (CsFAMA and CsFAMA-X).
Fig. 2: Surface and bulk characterization of perovskite films.
Fig. 3: Location of Na and F ions and effects on chemical bonding strength and formation energy of FA vacancies.
Fig. 4: Performance of PSCs.
Fig. 5: Stability performance of PSCs under various conditions.