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18 September 2018 Molecular origin of photostability for non-fullerene acceptors and its impact on solar cell performance (Conference Presentation)
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Non-fullerene acceptors (NFAs) provide an exciting alternative to traditional fullerene containing organic photovoltaics and are already out-competing fullerenes in terms of stability and efficiency. One class of NFA that has proved most promising is an A-D-A motif not dissimilar to a push/pull conjugated polymer. O-IDTBR, a planar A-D-A NFA has achieved the highest efficiency for a P3HT containing device, with an impressive 7.7% being obtained when in a ternary blend with a secondary twisted acceptor, O-IDFBR. Surprisingly this ternary blend not only shows an improvement in JSC, FF and VOC but also exhibits a greatly improved operational stability compared to the binary IDTBR:P3HT device. Our overarching goal is to understand this improved stability. Here we undertake the first steps to understanding the stability of these materials by studying the molecular origin of degradation for neat and blends containing these novel NFAs. We find by using in-situ resonant Raman spectroscopy, and supported by molecular DFT simulations, that both molecules undergo a two phase degradation. That being an oxygen mediated, photo-induced conformational change, most likely a torsion of the Core-BT dihedral, which then induces further irreversible degradation. It is also found that annealing O-IDTBR greatly enhances stability. We then investigate the miscibility of the two NFAs with P3HT and how this in-turn affects blend stability. The impact of such molecular conformational changes of these non-fullerene acceptors on device stability will be discussed.
Conference Presentation
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Ji-Seon Kim "Molecular origin of photostability for non-fullerene acceptors and its impact on solar cell performance (Conference Presentation)", Proc. SPIE 10737, Organic, Hybrid, and Perovskite Photovoltaics XIX, 107370Q (18 September 2018);

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