Local nanoscale phase impurities are degradation sites in halide perovskites

Stuart Macpherson, Tiarnan A. S. Doherty, Andrew J. Winchester, Sofiia Kosar, Duncan N. Johnstone, Yu-Hsien Chiang, Krzysztof Galkowski, Miguel Anaya, Kyle Frohna, Affan N. Iqbal, Satyawan Nagane, Bart Roose, Zahra Andaji-Garmaroudi, Kieran W. P. Orr, Julia E. Parker, Paul A. Midgley, Keshav M. Dani () and Samuel D. Stranks ()
Additional contact information
Stuart Macpherson: University of Cambridge
Tiarnan A. S. Doherty: University of Cambridge
Andrew J. Winchester: Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University
Sofiia Kosar: Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University
Duncan N. Johnstone: University of Cambridge
Yu-Hsien Chiang: University of Cambridge
Krzysztof Galkowski: University of Cambridge
Miguel Anaya: University of Cambridge
Kyle Frohna: University of Cambridge
Affan N. Iqbal: University of Cambridge
Satyawan Nagane: University of Cambridge
Bart Roose: University of Cambridge
Zahra Andaji-Garmaroudi: University of Cambridge
Kieran W. P. Orr: University of Cambridge
Julia E. Parker: Diamond Light Source, Harwell Science and Innovation Campus
Paul A. Midgley: University of Cambridge
Keshav M. Dani: Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University
Samuel D. Stranks: University of Cambridge

Nature, 2022, vol. 607, issue 7918, 294-300

Abstract: 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.

Date: 2022
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DOI: 10.1038/s41586-022-04872-1

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