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
a Aix-Marseille University, Centre Interdisciplinaire de Nanosciences de Marseille CINaM, UMR CNRS 7325, Marseille, France.
b Université Clermont Auvergne, CNRS, SIGMA Clermont, Institut de Chimie de Clermont-Ferrand, F-63000 Clermont−Ferrand, France
c Aix-Marseille Univ., Univ. Toulon, UMR CNRS 7334, Institut Matériaux Microélectronique Nanoscience de Provence (IM2NP), Marseille, France
d CEA, Institut de Recherche Interdisciplinaire de Grenoble IRIG, Laboratoire Systèmes Moléculaires et nano Matériaux pour l’Énergie et la Santé (SyMMES) , Grenoble, France
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Yatzil Avalos, 265
Publication date: 11th February 2019

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.

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