Non-fullerene acceptor photostability and its impact on organic solar cell lifetime

• Published in: Cell reports physical science 2021-07, Vol.2 (7), p.100498, Article 100498
• Main Authors: Clarke, Andrew J., Luke, Joel, Meitzner, Rico, Wu, Jiaying, Wang, Yuming, Lee, Harrison K.H., Speller, Emily M., Bristow, Helen, Cha, Hyojung, Newman, Michael J., Hooper, Katherine, Evans, Alex, Gao, Feng, Hoppe, Harald, McCulloch, Iain, Schubert, Ulrich S., Watson, Trystan M., Durrant, James R., Tsoi, Wing C., Kim, Ji-Seon, Li, Zhe
• Format: Article
• Language: English
• Subjects: IDTBR stability; ITIC stability; molecular conformation; non-fullerene acceptors; OPV stability; organic photovoltaics; photostability; Raman spectroscopy
• ISSN: 2666-3864; 2666-3864
• DOI: 10.1016/j.xcrp.2021.100498

The development of non-fullerene acceptors (NFAs) has facilitated the realization of efficient organic solar cells (OSCs) with minimal burn-in losses and excellent long-term stability. However, the role of NFA molecular structures on device stability remains unclear, limiting commercialization of NFA-based OSCs. Herein, the photostability of 10 OSC devices, fabricated with various NFAs (O-IDTBR, EH-IDTBR, ITIC, and ITIC-M) blended with donor polymers (PTB7-Th, PffBT4T-2OD, and PBDB-T), is investigated. O-IDTBR and EH-IDTBR form highly stable devices with all three polymers, whereas ITIC and ITIC-M devices suffer from burn-in losses and long-term degradation. Conformational instability is found to be responsible for the poor photostability of ITIC and ITIC-M, resulting in poor device stability. Twisting and potential breakage of the chemical bond that links the end group to the main backbone of ITIC and ITIC-M molecules causes undesirable conformational changes. Potential strategies to overcome such detrimental photo-induced conformational changes in NFAs are proposed. [Display omitted] Excellent photostability of O-IDTBR and EH-IDTBR results in good device stabilityITIC and ITIC-M have poorer photostability, resulting in reduced device lifetimesRaman spectroscopy reveals twisting and breakage of ITIC upon illumination in N2Vinylene linkage between the core and the end groups is a weak point of ITIC and ITIC-M Clarke et al. find that ITIC and ITIC-M can twist upon illumination in inert conditions, leading to eventual bond breakage and poor device stability. In contrast, O-IDTBR and EH-IDTBR devices show excellent stability. These findings provide insights that could aid with the design of more photostable acceptors.