Photodegradation study of ITIC derivatives acceptors and the correlation with stability in organic solar cells2

Yatzil Avalos^a, Agnès Rivaton^b, Carmen M. Ruiz^c, David Duché^c, Jean-Jacques Simon^c, Pavlo Perkhun^a, Olivier Margeat^a, Christine Videlot-Ackermann^a, Lydia Cabau^d, Olivier Bardagot^d, Renaud Demadrille^d, Jörg Ackermann^a

^aAix-Marseille University, CINAM CNRS UMR, Aix Marseille Université, Marseille, 13288, France

^bUniversité Clermont Auvergne, CNRS, SIGMA Clermont, Institut de Chimie de Clermont-Ferrand, F-63000 Clermont−Ferrand, France

^cAix-Marseille Univ., Univ. Toulon, UMR CNRS 7334, Institut Matériaux Microélectronique Nanoscience de Provence (IM2NP), Marseille, France

^dCEA, Institut de Recherche Interdisciplinaire de Grenoble IRIG, Laboratoire Systèmes Moléculaires et nano Matériaux pour l’Énergie et la Santé (SyMMES) , Grenoble, France, France

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)

Roma, Italy, 2020 May 12th - 14th

Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo

Poster, Yatzil Avalos, 265
Publication date: 6th February 2020

Intense research in the field of novel non-fullerene acceptors (NFA) has allowed to increase power conversion efficiency in organic photovoltaics over 17 %, making organic solar cells nowadays one of the most promising approaches for new generation PV ^[1]. Therefore, the long-term stability of these new photovoltaic materials, especially the identification of potential photodegradation processes, must be addressed now in details in order to prepare the way towards commercialisation.

Amongst the NFAs, there are two successful molecule classes based on linear A–D–A architectures^[2], which are derivatives of IDTBR on the one side, and ITIC and its various derivatives (ITIC-Th, ITIC-4F) in the other side. Recently the photostability of two acceptors of the IDTBR family has been studied, and it was shown that crystallinity arising from specific chemical structure design is essential for high photostability ^[3].

Here we focus on the photochemical stability of the second most important NFA classes based on the ITIC derivatives which have demonstrated wide application in highly efficient OSCs with many polymer donors, such PBDB-T (PCE12), PTB7-Th (PCE10) and the new halogenated derivative of PCE12, PBDB-T-2F (PCE13) ^[4] Recently Brabec and coll ^[5] have studied the stability of polymer solar cells using the ITIC derivatives (ITIC, ITIC-4F, ITIC-M, ITIC-DM, ITIC-Th). However, there is no analysis relating potential photodegradation processes in these materials to the device performance. It is known that the resistance to degradation mainly depends on the chemical structure of the active layer components, the crystallinity nature of the materials and species generated in the excited state.

In this work, we identified the ITIC derivates that are sensitive to thermal and photochemical rearrangements on the one hand. Especially, the sensitivity to singlet oxygen ¹O₂, a very reactive transient species which can dramatically affect the stability of the molecule ^[6],is addressed. Furthermore, we discuss the role of molecular structure and conformation on the acceptor stability under photochemical and thermal stress in presence (extrinsic stability) and in absence (intrinsic stability) of oxygen, in order to understand the degradation mechanisms in the core of the molecule itself. And finally, we correlate the observed degradation phenomenon of the different ITIC derivates with the device stability of organic solar cells using PCE-10, PCE-12 and PCE-13 as donor polymers.

References:

[1] L. Meng et al., “Organic and solution-processed tandem solar cells with 17.3% efficiency,” Science, vol. 361, no. 6407, pp. 1094–1098, 2018.

[2] Zhang et al. “Material insights and challenges for non-fullerene organic solar cells based on small molecular acceptors”, Nature Energy 3, 720–731, 2018

[3] Luke et al., “Twist and Degrade—Impact of Molecular Structure on the Photostability of Nonfullerene Acceptors and Their Photovoltaic Blends”, Adv. Energy Mater., pp. 1803755, February 2019

[4] H. Zhang et al., ”Over 14% Efficiency in Organic Solar Cells Enabled by Chlorinated Nonfullerene Small‐Molecule Acceptors” Adv. Mater., vol. 30 pp. 1800613, July 2018.

[5] X. Du et al., “Efficient Polymer Solar Cells Based on Non-fullerene Acceptors with Potential Device Lifetime Approaching 10 Years,” Joule, vol. 3, no. 1, pp. 215–226, Jan. 2019.

[6] A. Perthué et al., “An efficient and simple tool for assessing singlet oxygen involvement in the photo-oxidation of conjugated materials”. Solar Energy Materials & Solar Cells , 176, pp. 336-339, 2018.

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