Elemental mapping of perovskite cells using Transmission Electron Microscopy

Stefania Cacovich^a, Giorgio Divitini^a, Caterina Ducati^a, Fabio Matteocci^b, Aldo Di Carlo^b

^aUniversity of Cambridge - UK, The Old Schools, Trinity Ln, Cambridge CB2 1TN, UK, Cambridge, United Kingdom

^bCHOSE - Centre for Hybrid and Organic Solar Energy, University of Rome ‘‘Tor Vergata’’, Via del Politecnico, 1, Roma, Italy

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Poster, Giorgio Divitini, 132
Publication date: 5th February 2015

The emergence of perovskite-based solar cells determined a surge in both device synthesis and characterisation research, leading to the introduction of specialised techniques. The state of the art in Scanning Transmission Electron Microscopy (STEM) has recently evolved thanks to the introduction of high-brightness electron guns and high-yield x-ray detectors, improving its analytical capabilities. In conjunction with data processing carried out with machine learning algorithms for data denoising and analysis, these advancements now allow the study of materials, such as metal halide perovskites, which can be easily damaged under the electron beam. In this work we prepare fully functional solar cells for TEM analysis using focused ion beam milling, producing a thin, electron transparent, lamella, as shown in the attached figure. Energy-dispersed X-ray spectroscopy (EDX) in the STEM is used to obtain elemental maps with a spatial resolution of a few nm, while principal component analysis and independent component analysis are used to denoise the dataset and identify local variations in the chemical composition. Local perovskite stoichiometry is determined semi-quantitatively by measurement of the Pb / I ratio; the infiltration of perovskite in the supporting titania scaffold is also verified (see figure). Additionally, we investigate the effect of thermal treatments to the devices in situ in the STEM, obtaining morphologic and compositional information as the cell is degraded. This provides insight on the degradation pathways of the material, and gives valuable information that might be used to address long-term stability issues related to perovskite-based devices.
(Left) Cross-sectional view of a perovskite-based cell and (right) associated perovskite map.

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