Correlation of detailed photodegradation study of ITIC derivative acceptors in polymer blends and its impact on the stability in polymer solar cells.

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, Uyxing Vongsaysy^e, Mélanie Bertrand^e, 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

^dUniv. Grenoble Alpes, CEA, CNRS, IRIG, SyMMES, France

^eARMOR, Organic Photovoltaics Division, Armor Sustainable Energies (ASE), La Chevrolière, France

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting19 (NFM19)

#OPV19. Organic Photovoltaics: recent breakthroughs, advanced characterization and modelling

Berlin, Germany, 2019 November 3rd - 8th

Organizers: Jörg Ackermann and Uli Würfel

Oral, Yatzil Avalos, presentation 368
DOI: https://doi.org/10.29363/nanoge.nfm.2019.368
Publication date: 18th July 2019

Intense research in the field of novel non-fullerene acceptors (NFAs) has allowed to increase the 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 depth to prepare the way towards commercialization.

Amongst 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) on the other side. Recently, the photostability of two IDTBR derivatives has been studied, and it has been shown that crystallinity arises from specific chemical structure design is essential for high photostability ^[3].

Here we present a detailed study of photochemical and thermal stability of photoactive layers composed of ITIC derivatives NFAs blended with 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 ITIC derivatives (ITIC, ITIC-4F, ITIC-M, ITIC-DM, ITIC-Th). However, there is no analysis relating potential photodegradation processes to the device performance. The stability of high efficiency solar cells using PCE13 as donor have not yet been studied deeply. 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 study the stability of ITIC derivates en details in thin layers as well as in polymer solar cells.. Especially, we focus on their 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. The degradation kinetics of the ITIC derivates in polymer blends are compared to pure acceptor in order to study potential stabilization effects in the bulk heterojunction. The obtained degradation kinetics of the different ITIC derivates is then compared to the degradation of the corresponding solar cells. The device stability of high efficiency solar cells of over 12% using PCE-10, PCE-12 and PCE-13 as donor polymers are compared to solar cells using IDTBR as acceptor.

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] J. 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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