Presentation Details
| On the Validity of Superposition Principle and Series Resistance for Perovskite Solar Cells Andreas Fell1, Oliver Fischer1, 2, Johannes Greulich1, Christoph Messmer1, 2, Hannah Davidson1, Martin C.Schubert1, Stefan W.Glunz1, 2. 1Fraunhofer Institute for Solar Energy Systems, Freiburg, Germany.2INATECH, University of Freiburg, Freiburg, Germany |
Abstract
Accurate electrical characterization of perovskite solar cells (PSCs) remains challenging compared to silicon solar cells. This is caused by strong metastabilities, fast degradation during measurement, and limited reproducibility, as well as by fundamentally different and still incompletely understood device physics. PSCs are thin-film devices that typically lack a quasi-neutral bulk region dominating the device thickness. As a result, common simplifying assumptions used in silicon photovoltaics—such as vertically uniform quasi-Fermi-level splitting, and the superposition principle—are often invalid. Nevertheless, many established electrical characterization techniques implicitly rely on these assumptions, raising concerns about the validity of extracted device parameters when applied to PSCs. In this work, the interpretation of key electrical characterization methods, namely JV and suns-Voc (or suns-PL) measurements, is critically examined using device simulations and experimental data. Particular emphasis is placed on the superposition principle, which underlies the determination of series resistance from different JV curves and is implicitly assumed in equivalent-circuit-model analysis. The simulations reveal multiple indications of superposition violation, including large variations in extracted series resistance depending on the evaluation method, discrepancies between Voc and implied Voc that are incompatible with a simple series resistance concept, and further strong differences between equivalent-circuit internal voltages and the actual quasi-Fermi-level splitting. A characteristic manifestation of this violation is an apparent shunt (“photo-shunt”), visible only in illuminated JV curves. This feature originates from voltage-dependent coupled recombination and transport losses. Similar behavior is frequently observed in experimental PSC devices, suggesting that superposition violation may be a general property of PSCs. Consequently, characterization techniques relying on superposition, like series and shunt resistance determination, should be interpreted with caution.
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No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the author.