A detailed stability study of highly efficient polymer solar cells based on ITIC derivatives
Elena Barulina a b, Pavlo Perkhun a, Wolfgang Köntges c, Martin Pfannmöller c, Sadok Ben Dkhil b, Jean-Jacques Simon d, Olivier Margeat a, Christine Videlot-Ackermann a, Jörg Ackermann a
a Aix-Marseille Univ., UMR CNRS 7325, Centre Interdisciplinaire de Nanosciences de Marseille (CINaM), 13009 Marseille Cedex 09, France
b Dracula Technologies, 4 rue Georges Auric, 26000 Valence, France
c Centre for Advanced Materials (CAM), Heidelberg University, Heidelberg, Germany
d Aix-Marseille Univ., Univ. Toulon, UMR CNRS 7334, Institut Matériaux Microélectronique Nanoscience de Provence (IM2NP), Marseille, 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
Oral, Elena Barulina, presentation 115
DOI: https://doi.org/10.29363/nanoge.hopv.2019.115
Publication date: 11th February 2019

   Today, organic solar cells are alternative energy sources, which are now competitive for an introduction into a new generation photovoltaic market due to their high performance, processing on a large surface, flexibility and low price. There has been considerable research that allowed very recently to achieve certified power conversion efficiency over 17% in a tandem organic solar cells [1]. This tremendous increase for organic photovoltaics during the last two years was enabled by the development of novel non-fullerene acceptor (NFA) materials that outperform fullerene-based acceptors. However, the long-term stability of these new photovoltaic materials and the corresponding devices is a key factor to figure out the commercial viability and must be addressed in detail.

   While some works on new NFAs mentioned improved stability of NFA based solar cells under specific conditions (storage in air or under LED light soaking), the work of Brabec and coll. [2] has very recently provided a study dedicated to one of the most important new NFA family, namely the ITIC derivatives (ITIC, ITIC-4F, ITIC-M, ITIC-DM, ITIC-Th) indicating the fluorinated acceptor are most stable. However, the stability of the solar cells was only studied under LED light, while standard tests such as ISOS-D-2 High-temperature storage as well as ISOS-L-1 (Laboratory weathering under continuous illumination at AM 1.5) [3] were missing.

   Previously, we investigated the stability of solar cells based on PTB7 and fullerene derivatives depending on interfacial layers [4], [5] and thermal treatments. The aim of this work is to study in detail the stability of high efficiency organic solar cells using different ITIC derivatives by applying the three standard tests and compare the degradation processes of NFA based solar cells under illumination at AM 1.5 and LED.  Furthermore, in order to compare the NFA to fullerene acceptors, we developed a PCE10:PC70BM blend system that is fully stable [6] under ISOS-L-1 conditions. This demonstrates the stability of our device structure including interfacial layers and allows to evaluate the NFA related degradation processes in the corresponding solar cells. The stabilized PCE-10:PC70BM solar cells are compared to PCE-12:ITIC, PBDBT-F:ITIC-4F, Furthermore, detailed characterizations of the device degradation in relation to the morphology will be discussed using atomic force microscopy and spectral imaging analyses from analytical scanning transmission electron microscopy. Whilst PCE-10:PC70BM solar cells are found to be stable with an efficiency of 7%, we show that both ITIC:PCE-12 and ITIC-4F:PBDBT-F solar cells with performances of 10% and 11%, respectively, degrade very fast under simulated AM 1.5 illumination. LED light clearly reduced device degradation. We also discuss thermal treatment techniques aiming to improve the stability of ITIC based solar cells by improving the crystallinity of the polymer blend.

Figure 1 The stability of encapsulated device under continuous illumination at 1.5 AM lamp in an air

The research is supported by CIFRE Agreement 2017/0529 between Dracula Technologies and CINaM.

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