Local nanoscale phase impurities are degradation sites in halide perovskites

DOI: 10.1038/s41586-022-04872-1

Authors: Stuart Macpherson (University of Cambridge) , Tiarnan A. S. Doherty (University of Cambridge) , Andrew J. Winchester (Okinawa Institute of Science and Technology Graduate University) , Sofiia Kosar (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) , Paul A. Midgley (University of Cambridge) , Keshav M. Dani (Okinawa Institute of Science and Technology Graduate University) , Samuel D. Stranks (University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Nature

State: Published (Approved)
Published: May 2022
Diamond Proposal Number(s): 24111 , 20420

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% in single junction and 29.8% 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 photo-excited carriers which themselves reduce performance4,5, but via the same trapping process are sites at which photochemical degradation of the absorber layer is seeded. We visualise 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 film composition and processing, with the presence of polytypes being most detrimental for film photo-stability. Importantly, we reveal that performance losses and intrinsic degradation processes can both 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.

Journal Keywords: Imaging techniques; Solar cells

Diamond Keywords: Photovoltaics; Semiconductors

Subject Areas: Materials, Energy, Chemistry

Diamond Offline Facilities: Electron Physical Sciences Imaging Centre (ePSIC)
Instruments: E02-JEM ARM 300CF , I14-Hard X-ray Nanoprobe

Added On: 27/05/2022 08:30

Discipline Tags:

Surfaces Earth Sciences & Environment Sustainable Energy Systems Energy Physics Climate Change Physical Chemistry Energy Materials Chemistry Materials Science interfaces and thin films Perovskites Metallurgy

Technical Tags:

Diffraction Microscopy Electron Microscopy (EM) Scanning Transmission Electron Microscopy (STEM)