Twist and Degrade—Impact of Molecular Structure on the Photostability of Nonfullerene Acceptors and Their Photovoltaic Blends

Joel Luke, Emily M. Speller, Andrew Wadsworth, Mark F. Wyatt, Stoichko Dimitrov, Harrison K. H. Lee, Zhe Li, Wing C. Tsoi, Iain McCulloch, Diego Bagnis, James R. Durrant, Ji-Seon Kim

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96 Scopus citations


Nonfullerene acceptors (NFAs) dominate organic photovoltaic (OPV) research due to their promising efficiencies and stabilities. However, there is very little investigation into the molecular processes of degradation, which is critical to guiding design of novel NFAs for long-lived, commercially viable OPVs. Here, the important role of molecular structure and conformation in NFA photostability in air is investigated by comparing structurally similar but conformationally different promising NFAs: planar O-IDTBR and nonplanar O-IDFBR. A three-phase degradation process is identified: i) initial photoinduced conformational change (i.e., torsion about the core–benzothiadiazole dihedral), induced by noncovalent interactions with environmental molecules, ii) followed by photo-oxidation and fragmentation, leading to chromophore bleaching and degradation product formation, and iii) finally complete chromophore bleaching. Initial conformational change is a critical prerequisite for further degradation, providing fundamental understanding of the relative stability of IDTBR and IDFBR, where the already twisted IDFBR is more prone to degradation. When blended with the donor polymer poly(3-hexylthiophene), both NFAs exhibit improved photostability while the photostability of the polymer itself is significantly reduced by the more miscible twisted NFA. The findings elucidate the important role of NFA molecular structure in photostability of OPV systems, and provide vital insights into molecular design rules for intrinsically photostable NFAs.
Original languageEnglish (US)
Pages (from-to)1803755
JournalAdvanced Energy Materials
Issue number15
StatePublished - Feb 21 2019

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The authors acknowledge the UK EPSRC for the Plastic Electronics Centre for Doctoral Training (EP/L016702/1) funding and CSEM Brasil for studentship. This research was also supported by Global Research Laboratory (GRL) Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF-2017K1A1A2013153). E.M.S., W.C.T., and Z.L. thank the National Research Network in Advanced Engineering Materials (grant number NRN093), the Welsh Assembly Government funded Ser Cymru Solar Project, and UK EPSRC (EP/M025020/1). The authors thank John de Mello and James Bannock of Imperial College London for providing some of the P3HT used, and the Imperial College High-Performance Computing Service for DFT calculations.


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