Influence of Non-Fullerene Acceptors on the Photostability of Organic Photovoltaics in Inert Atmospheres

Andrew Clarke^a, Rico Meitzner^b, Joel Luke^c, Emily Speller^a, Hyojung Cha^d, Jiaying Wu^d, Helen Bristow^d, Yuming Wang^e, Katherine Hooper^a, Alex Evans^f, Feng Gao^e, Harald Hoppe^b, Ji-Seon Kim^c, Iain McCulloch^d^,^g, Ulrich Schubert^b^,^h, Trystan Watson^a, James Durrant^a^,^d, Wing Chung Tsoi^a, Zhe Li^f

^aSPECIFIC, College of Engineering Swansea University, SPECIFIC, Baglan Bay Innovation Centre, Central Avenue, Baglan, Port Talbot, SA12 7AX, United Kingdom

^bFriedrich Schiller University Jena, Germany, Jena, Germany

^cDepartment of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London, United Kingdom

^dDepartment of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London, United Kingdom

^eLinköping University, Sweden, SE-581 83, Linköping, Sweden

^fCardiff University, School of Engineering, UK, The Parade, United Kingdom

^gKing Abdullah University of Science and Technology (KAUST) - Saudi Arabia, 4700 King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia

^hFriedrich Schiller University Jena, Germany, Jena, Germany

Proceedings of International Conference on Advances in Organic and Hybrid Electronic Materials (AOHM19)

Dubrovnik, Croatia, 2019 March 17th - 20th

Organizers: Alejandro Briseno, Thuc-Quyen Nguyen and Natalie Stingelin

Oral, Andrew Clarke, presentation 022
DOI: https://doi.org/10.29363/nanoge.aohm.2019.022
Publication date: 8th January 2019

Many organic photovoltaic devices suffer from an irreversible deterioration in performance when illuminated by 1 sun irradiation in inert atmospheres. This is typically a biphasic degradation with a rapid initial drop in the first few 10’s of hours, followed by a slower phase of degradation that continues indefinitely during irradiation. Recently, with the development of new non-fullerene acceptors (NFAs), burn-in free devices have been demonstrated and T80 lifetimes of almost 10 years have been reached.[1,2] Yet, it is not fully understood why these systems show superior stability. In this study we have systematically tested a range of benchmark NFAs in combination with several high-performance donor polymers and found that the device photostability is highly dependent on the chosen acceptor. Photoluminescence, electroluminescence, UV-vis and Raman spectroscopy were used alongside transient photovoltage measurements to investigate the degradation processes. Of the investigated NFAs, Eh-IDTBR and O-IDTBR showed the most promise with excellent photostability when used in combination with PCE10, PCE11 and PCE12. This was attributed to exceptional photochemical and morphological stability. Other devices based on ITIC and M-ITIC were much less stable and lost up to 40% of their initial performance in less than 5 days of light soaking in a nitrogen atmosphere. Chemical degradation of the acceptor and morphological evolution were both demonstrated to be contributing factors to this loss of performance. Whilst it may be possible to resolve morphological instability by modifying device fabrication procedures, photochemical stability is a more fundamental property of a material. We show that by utilising Raman spectroscopy, it may be possible to identify the degradation location on NFA molecules. This information could allow for improved molecular design and the development of more photochemically stable NFAs.

References:

[1] Cha, H.; Wu, J.; Wadsworth, A.; Nagitta, J.; Limbu, S.; Pont, S.; Li, Z.; Searle, J.; Wyatt, M. F.; Baran, D.; Kim J.-S.; McCulloch I.; Durrant J. R. An Efficient, “Burn in” Free Organic Solar Cell Employing a Nonfullerene Electron Acceptor. Adv. Mater. 2017, 29, 1701156.

[2] Du X.; Heumueller T.; Gruber W.; Classen A.; Unruh T.; Li N.; Brabec C. J. Efficient Polymer Solar Cells Based on Non-fullerene Acceptors with Potential Device Lifetime Approaching 10 Years. Joule 2018, In Press.

Acknowledgements:

The authors would like to thank all sources of funding that made this work possible including funding from the European Social Fund via the Welsh Government, EPSRC projects EP/L015099/1 & EP/M025020/1, Innovate UK project 133701, the Welsh Assembly Government of the Ser Cymru Solar Program, the Welsh Assembly Government Ser Cymru II Fellowship Scheme, the National Research Network in Advanced Engineering and Materials and Eight19.

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