Abstract
Understanding the nanoscopic chemical and structural changes that drive instabilities in emerging energy materials is essential for mitigating device degradation. The power conversion efficiency of halide perovskite photovoltaic devices has reached 25.7 per cent in single-junction and 29.8 per cent in tandem perovskite/silicon cells1,2, yet retaining such performance under continuous operation has remained elusive3. Here we develop a multimodal microscopy toolkit to reveal that in leading formamidinium-rich perovskite absorbers, nanoscale phase impurities, including hexagonal polytype and lead iodide inclusions, are not only traps for photoexcited carriers, which themselves reduce performance4,5, but also, through the same trapping process, are sites at which photochemical degradation of the absorber layer is seeded. We visualize illumination-induced structural changes at phase impurities associated with trap clusters, revealing that even trace amounts of these phases, otherwise undetected with bulk measurements, compromise device longevity. The type and distribution of these unwanted phase inclusions depends on the film composition and processing, with the presence of polytypes being most detrimental for film photo-stability. Importantly, we reveal that both performance losses and intrinsic degradation processes can be mitigated by modulating these defective phase impurities, and demonstrate that this requires careful tuning of local structural and chemical properties. This multimodal workflow to correlate the nanoscopic landscape of beam-sensitive energy materials will be applicable to a wide range of semiconductors for which a local picture of performance and operational stability has yet to be established.
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Data availability
The data that support the findings of this study are available at https://doi.org/10.17863/CAM.85310 or from the corresponding authors upon request.
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Acknowledgements
S.M. acknowledges funding from an Engineering and Physical Sciences Research Council (EPSRC) studentship and support from the Japan Society for the Promotion of Science (JSPS) Summer Fellowship Programme. T.A.S.D. acknowledges the support of a National University of Ireland Travelling Studentship and an Oppenheimer Research Fellowship. S.D.S. acknowledges the Royal Society and Tata Group (UF150033). The work has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme (HYPERION - grant agreement number 756962). Z.A.-G. acknowledges funding from a Winton Studentship and an ICON Studentship from the Lloyd’s Register Foundation. Y.H.-C. thanks the Cambridge Trust for a studentship and acknowledges the Taiwan Cambridge Trust and Rank Prize. We acknowledge the EPSRC (EP/R023980/1, EP/V012932/1, EP/T02030X/1 and EP/S030638/1) for funding. K.F. acknowledges a George and Lilian Schiff Studentship, a Winton Studentship, a EPSRC studentship, a Cambridge Trust Scholarship and a Robert Gardiner Scholarship. M.A. acknowledges funding from the Marie Skłodowska-Curie actions (grant agreement number 841386) under the European Union’s Horizon 2020 research and innovation programme. K.W.P.O. acknowledges an EPSRC studentship. A.N.I. acknowledges a scholarship from the British Spanish Society. K.G. acknowledges support from the Polish Ministry of Science and Higher Education within the Mobilnosc Plus program (grant number 1603/MOB/V/2017/0). P.A.M. thanks the EPSRC for funding under grant numbers EP/R008779/1 and EP/V007750/1, and the European Union Horizon 2020 research and innovation programme (ESTEEM3): 823717. A.J.W., S.K. and K.M.D. acknowledge that this work was supported by the Femtosecond Spectroscopy Unit of the Okinawa Institute of Science and Technology Graduate University and JSPS Kakenhi Grant Number JP19K05637. We acknowledge the support for this work from the Imaging Section and Engineering Support Section of the Okinawa Institute of Science and Technology Graduate University. We acknowledge the Cambridge Royce facilities grant EP/P024947/1 and Sir Henry Royce Institute - recurrent grant EP/R00661X/1, and the Centre for Advanced Materials for Integrated Energy Systems (CAM-IES, EP/P007767/1). We thank Diamond Light Source for access and support in use of the electron Physical Science Imaging Centre (Instrument E02 and proposal number MG24111) and for providing beamtime at the I14 Hard X-ray Nanoprobe (proposal SP20420), which each contributed to the results presented here.
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S.M. prepared samples and collected, analysed and interpreted PEEM, steady-state PL, confocal TRPL and optical absorption data, and collected SED and nXRD data. T.A.S.D. prepared samples and collected, analysed and interpreted SED, high-angle annular dark-field, STEM-energy dispersive X-ray and nXRD data. A.J.W. collected, analysed and interpreted PEEM data. S.K. collected, analysed and interpreted PEEM and SEM data. D.N.J. collected, analysed and interpreted SED data. Y.-H.C. prepared devices, and collected device data and XRD data. K.G. collected and interpreted confocal TRPL data. M.A. and K.F. collected and interpreted nXRD data. A.N.I. collected and analysed SED data. S.N. prepared samples. B.R. collected SEM data. Z.A.-G. prepared samples. K.W.P.O. and J.E.P. collected nXRD data. P.A.M. supervised D.N.J. and assisted in the interpretation of SED data. K.M.D. supervised A.J.W. and S.K. S.D.S. supervised S.M., T.A.S.D., Y.-H.C., A.N.I., M.A., K.F., S.N., B.R. and Z.A.-G. S.D.S. conceived and designed the work. S.M., T.A.S.D. and S.D.S. produced first drafts and all authors contributed to editing the manuscript.
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S.D.S. is a co-founder of Swift Solar, Inc.
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41586_2022_4872_MOESM3_ESM.gif
Supplementary Video 1 SED data showing a pristine perovskite grain with an epitaxially aligned PbI2 inclusion at the grain boundary. Local diffraction patterns (right, scale bar, 0.75 Å−1) are extracted from the location of the red circle in the diffraction sum image (left, scale bar, 100 nm).
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Macpherson, S., Doherty, T.A.S., Winchester, A.J. et al. Local nanoscale phase impurities are degradation sites in halide perovskites. Nature 607, 294–300 (2022). https://doi.org/10.1038/s41586-022-04872-1
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DOI: https://doi.org/10.1038/s41586-022-04872-1
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