This result is consistent with the average radius of 9.5 ± 2.5 nm obtained for these fibers from the freeze-dried samples. On the other hand, for PM7 D1 and D2, as previously mentioned, there is no contribution from fiber-like aggregates but instead their Porod region at low Q was fitted to a power law model giving slopes between -2 and -3 suggesting their network-like aggregated structures (Table ). In PM7, we also observe the power law contribution at high Q as shown in Fig. , but it is not clear from the scattering plot due to the presence of Guinier knee region from the fiber aggregates; however, at a high solution temperature, we will later see that the power law region becomes clearer when these fiber aggregates are dissolved. This suggests that in PM7 solution, there are large fiber-like aggregates as well as some network-like structures while for PM7 D1 and D2, we mainly observe the polymer network-like aggregates. Furthermore, all polymer solutions contain a broad structure factor peak corresponding to the side chain interaction or weak lamellar stacking at high Q which was fitted with a pseudo-Voigt peak as shown in the deconvolution curves (Fig. ). Based on the pseudo-Voigt peak locations as shown in Table , the lamellar stacking distance is calculated to be 3.8 nm for PM7, while PM7 D1 and D2 polymers have lamellar stacking distances of 3.4 nm and 3.5 nm. These values are larger than the lamellar stacking distance of 2.1 nm observed in the blend films as shown later obtained through Grazing Incidence Wide Angle X-ray Scattering (GIWAXS), which could be due to the swelling of the lamella in the solutionstate. Besides side chain interactions observed in SAXS, we also determined that the polymer aggregates in all three solutions exhibit backbone stacking using TEM based electron diffraction measurements on the freeze-dried samples (Fig. ). These measurements show that the backbone stacking distance for PM7 is the shortest, around 4.5 Å, while for PM7 D1 and D2, the distances are slightly longer, 4.8 Å and 5.0 Å, respectively, indicating their weaker backbone interactions. These backbone stacking distances observed from the electron diffraction measurements are much larger than the π-π stacking distances observed in the film, which is around 3.5 Å from GIWAXS, suggesting weak interchain packing in the solution-state. Based on the aforementioned model fitting, we were also able to obtain the persistence lengths for the polymer chains as summarized in Table . The results suggest that PM7 has the highest persistence length around 32.6 nm while PM7 D1 and D2 have persistence lengths around 7-10 nm. The rigidity of PM7 may be attributed to its highly planar BDD and conformationally locked acceptor core which has been shown to induce strong aggregation and backbone planarity in other polymer systems. However, we also predict that the ester functionalized terthiophene moieties of PM7 D1 and D2 polymers may contribute to their backbone flexibility.