“…Pristine PBDB-T used as a donor shows Raman modes at 1,427, 1,452, 1,487, and 1,540 cm −1 , which are assigned to the C α =C β symmetric stretching mode, antisymmetric stretch mode of C α =C β , skeletal stretching mode of C β -C β and antisymmetric C α -S-C α ring skeleton that depict distortion of the in-plane vibrations of the thiophene ring of PBDB-T (Gao et al, 2018). Other less intense peaks are at 1,075, 1,231, and 1,598 cm −1 and may be assigned to the stretching mode of C β -C alkyl , C-H bending mode, and antisymmetric stretch mode of C α =C β , respectively (Kabongo et al, 2016). Upon blending with acceptor materials, there is no noticeable shift in peak position regardless of whether ITIC-Th (nonfullerene) nor PC 71 BM (fullerene) is used.…”