Standardized Protocols for Evaluating Mechanical Performance of Flexible Solar Cells & Modules: Insights from new Procedures ISOS-B, ISOS-M, and Novel Bending Tests

Luigi Angelo Castriotta^a^,^b, Kenjiro Fukuda^c^,^d, Osbel Almora^e, Lulu Sun^d, Md Aslam Uddin^f, Haoyang Jiao^f, Karen Forberich^g, Christoph J. Brabec^g^,^h, Jinsong Huang^b^,ⁱ

^aCHOSE – Centre for Hybrid and Organic Solar Energy, Department of Electronic Engineering, Tor Vergata University of Rome, via del Politecnico 1, 00133, Rome

^bDepartment of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA

^cRIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama, Japan

^dThin-Film Device Laboratory, RIKEN, Wako, Saitama, Japan

^eDepartment of Electronic, Electrical and Automatic Engineering, Universitat Rovira i Virgili, Tarragona, Spain

^fPerotech Inc, 125 South Rd., Kenan Lab B825, Chapel Hill, NC 27599-3050, USA

^gForschungszentrum Jülich GmbH, Department of High Throughput Methods in Photovoltaics, Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (HI ERN), Erlangen, Germany

^hInstitute of Materials for Electronics and Energy Technology (i-MEET), Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany

ⁱDepartment of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA

Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV25)

Roma, Italy, 2025 May 12th - 14th

Organizers: Filippo De Angelis, Francesca Brunetti and Claudia Barolo

Oral, Luigi Angelo Castriotta, presentation 119
Publication date: 17th February 2025

The advancement of flexible photovoltaic (PV) technologies needs the establishment of standardized protocols for their characterization, particularly concerning mechanical performance and durability. Here we show newly proposed standard procedures such as ISOS-B, ISOS-M and a new protocol for measuring PCE over 1000 bending cycles under 1% strain, which aim to complete existing guidelines such as IEC 61215 and IEC 61646.
ISOS-B focus on bending stress testing. This protocol is crucial for accurately assessing the mechanical stability of flexible PV devices, which can exhibit negligible degradation even under extreme bending conditions. ISOS-M addresses mechanical and long-term stability under various environmental conditions, suggesting tests in controlled ambient conditions to isolate the effects of mechanical stress from other environmental factors. This is essential for understanding how flexible devices perform over time, especially when exposed to real-world conditions. We further evaluate the need to measure the mechanical stability of a flexible device independently from the thickness and on the material properties of the substrate, by calculating its strain and defining a new figure of merit called fatigue factor. The introduction of a fatigue factor quantifies the mechanical performance of flexible PV devices, facilitating objective comparisons of durability and efficiency. This factor allows researchers to evaluate the relationship between mechanical stress and electrical performance. In conclusion, by improving upon existing IEC guidelines, these standards provide a robust framework for evaluating the mechanical and environmental performance of flexible PV technologies, ultimately contributing to their commercialization and integration into different applications. The integration of these standardized procedures fosters advancements in flexible photovoltaics, leading to improved device reliability and performance in practical applications.

References:

[1] L.A. Castriotta, Md A. Uddin, H. Jiao, J. Huang, Transition of Perovskite Solar Technologies to Being Flexible. Adv. Mater. 2025, 2408036

[2] K. Fukuda, L. Sun, B. Du, M. Takakuwa, J. Wang, T. Someya, L. F. Marsal, Y. Zhou, Y. Chen, H. Chen, S. Ravi P. Silva, D. Baran, L. A. Castriotta, T. M. Brown, C. Yang, W. Li, A. W. Y. Ho-Baillie, T. Österberg, N. P. Padture, K. Forberich, C. J. Brabec, O. Almora, A bending test protocol for characterizing the mechanical performance of flexible photovoltaics. Nat Energy 9, 1335–1343 (2024).

[3] O. Almora, G. C. Bazan, C. I. Cabrera, L. A. Castriotta, S. Erten-Ela, K. Forberich, K. Fukuda, F. Guo, J. Hauch, A. W. Ho-Baillie, T. J. Jacobsson, R. A. Janssen, T. Kirchartz, R. R. Lunt, X. Mathew, D. B. Mitzi, M. K. Nazeeruddin, J. Nelson, A. F. Nogueira, U. W. Paetzold, B. P. Rand, U. Rau, T. Someya, C. Sprau, L. Vaillant-Roca, C. J. Brabec, Device Performance of Emerging Photovoltaic Materials (Version 5). Adv. Energy Mater. 2024, 2404386.

[4] L. A. Castriotta, F. De Rossi, M. Bonomo, Game-Changers for Flexible Perovskite Solar Cells and Modules: Elastomers and Cross-Linking Molecules. ACS Energy Letters 2025 10 (1), 283-286.

[5] L. Sun, K. Fukuda, R. Guo, L. A. Castriotta, K. Forberich, Y. Zhou, T. Someya, C. J. Brabec, O. Almora, A Flexible Photovoltaic Fatigue Factor for Quantification of Mechanical Device Performance. Adv. Funct. Mater. 2025, 2422706.

Acknowledgements:

This project has received funding from the European Union’s Framework Programme for Research and Innovation Horizon Europe (2021-2027) under the Marie Sklodowska-Curie Grant Agreement No. 101068387 EFESO.

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