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6 1 I H I G H L I G H T S 2 0 2 3

PRINCIPAL PUBLICATION AND AUTHORS

On the Importance of Chemical Precision in Organic Electronics: Fullerene Intercalation in Perfectly Alternating Conjugated Polymers, J. Vanderspikken (a,b,c), Z. Liu (d), X. Wu (e), O. Beckers (a,b,c), S. Moro (f), T.J. Quill (g), Q. Liu (a,b,c), A. Goossens (a,b,c), A. Marks (g), K. Weaver (h), M. Hamid (i), B. Goderis (i), E. Nies (i), V. Lemaur (j), D. Beljonne (j), A. Salleo (g), L. Lutsen (a,b,c), K. Vandewal (a,b,c), B. Van Mele (d), G. Costantini (f), N. Van den Brande (d), W. Maes (a,b,c), Adv. Funct. Mater. 2309403 (2023); https:/doi.org/10.1002/adfm.202309403 (a) Institute for Materials Research (IMO), Hasselt University, Agoralaan, Diepenbeek (Belgium) (b) IMEC, Associated Lab IMOMEC, Diepenbeek (Belgium) (c) Energyville, Thorpark, Genk (Belgium) (d) Vrije Universiteit Brussel, Physical Chemistry and Polymer Science, Brussels (Belgium) (e) Department of Chemistry, University of Warwick, Coventry (UK) (f) School of Chemistry, University of Birmingham, Birmingham (UK) (g) Department of Materials Science and Engineering, Stanford University, Stanford (USA) (h) Department of Earth System Science, Stanford University, Stanford (USA) (i) KU Leuven, Polymer Chemistry and Materials Division, Heverlee (Belgium) (j) Laboratory for Chemistry of Novel Materials, Materials Research Institute, University of Mons, Mons (Belgium)

supported by molecular dynamics (MD) simulations and juxtaposed to benchmark PBTTT.

Synchrotron XRD experiments were carried out at beamline BM26. Figure 42a shows three prominent reflections highlighted in the small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) plots of defect-free PBTTT-(OR)2 using dashed black lines. The corresponding d-spacings at 25°C and 150°C are shown in Figure 42b and compared with values calculated from the MD simulated structures (Figure 43). Limited or partial intercalation for the defective PBTTT-(OR)2 is evidenced by the absence of a SAXS peak at the typical q-values for perfectly intercalated co-crystals and a shift to higher q-values close to the pure polymer (Figure 42c). The analysis shows that homocoupling is detrimental

for geometrical rather than electronic reasons, as it hinders fullerene intercalation in PBTTT-(OR)2, whereas intercalation is recovered for the homocoupling-free polymer. This is also reflected at the device level, where enhanced charge-transfer absorption was observed for the mixture of defect-free PBTTT-(OR)2 and PC61BM, whereas it was significantly reduced for the defective analogue.

In conclusion, this study clearly demonstrates that structural defects do matter and should be generally avoided, in particular when the geometrical regularity of the polymer is essential. It also introduces a generic synthetic strategy to avoid homocoupling errors. These insights likely go beyond the specific PBTTT derivatives studied here and are of general relevance for the wider organic electronics field.

Fig. 43: Representation of the simulated organisations of neat PBTTT-(OR)2 (left) and PBTTT- (OR)2 mixed with PC61BM (right) at 25°C and 150°C (last snapshots of 1 ns-long molecular dynamics). Size indications are provided in Figure 42b.