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Interpretation of inverted photocurrent transients in organic lead halide perovskite solar cells: proof of the field screening by mobile ions and determination of the space charge layer widths

Rebecca A. Belisle, William H. Nguyen, Andrea R. Bowring, Philip Calado, Xiaoe Li, Stuart Irvine Orcid Logo, Michael D. McGehee, Piers R. F. Barnes, Brian C. O'Regan

Energy and Environmental Science, Volume: 10, Issue: 1, Pages: 192 - 204

Swansea University Author: Stuart Irvine Orcid Logo

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DOI (Published version): 10.1039/C6EE02914K

Abstract

In Methyl Ammonium Lead Iodide (MAPI) perovskite solar cells, screening of the built-in field by mobile ions has been proposed as part of the cause of the large hysteresis observed in the current/voltage scans in many cells. We show that photocurrent transients measured immediately (e.g. 100 μs) aft...

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Published in: Energy and Environmental Science
ISSN: 1754-5692 1754-5706
Published: 2017
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URI: https://cronfa.swan.ac.uk/Record/cronfa31836
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Abstract: In Methyl Ammonium Lead Iodide (MAPI) perovskite solar cells, screening of the built-in field by mobile ions has been proposed as part of the cause of the large hysteresis observed in the current/voltage scans in many cells. We show that photocurrent transients measured immediately (e.g. 100 μs) after a voltage step can provide direct evidence that this field screening exists. Just after a step to forward bias, the photocurrent transients are reversed in sign (i.e. inverted), and the magnitude of the inverted transients can be used to find an upper bound on the width of the space charge layers adjacent to the electrodes. This in turn provides a lower bound on the mobile charge concentration, which we find to be ≳1 × 1017 cm−3. Using a new photocurrent transient experiment, we show that the space charge layer thickness remains approximately constant as a function of bias, as expected for mobile ions in a solid electrolyte. We also discuss additional characteristics of the inverted photocurrent transients that imply either an unusually stable deep trapping, or a photo effect on the mobile ion conductivity.
Keywords: Perovskite solar cells; Ammonium iodide; Electric charge; Electric space charge; Electrolytes; Ionic conduction; Ions; Perovskite; Photocurrents; Solar cells; Solid electrolytes; Transients Built-in fields; Forward bias; Large hysteresis; Lower bounds; Mobile charge; Photo effect; Photocurrent transients; Space charge layers
College: Faculty of Science and Engineering
Issue: 1
Start Page: 192
End Page: 204

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