To support our picture of the conjugated polymer solution state, we use additional techniques such as SEM and AFM freeze-dried imaging and UV-Vis spectroscopy. By freezedrying the PII-2T solutions in a liquid propane-ethane mixture and sublimating the solvent we are able to preserve the solution state structure and image it using SEM (Figure ) and AFM (Figure ). The AFM measurements are used to measure the fibril height in the out of plane direction. AFM linecuts are indicated by the dashed cyan line with the corresponding height profile shown in Figure . Linecuts were chosen in regions with few overlapping fibrils for more accurate measurements. For low MW PII-2T, SEM imaging reveals that in CB the conjugated polymer forms fibril structures in solution with fibril widths of ~10 to several 10's of nm in plane. From AFM imaging, fibril heights out-of-plane are shown to be primarily from 10 to 20 nm, which is in agreement with the in-plane width estimated from SEM and also the crosssectional Guinier plot in Figure (yielding a diameter of 12.8 nm). It is important to note that while the SEM imaging appears to show several fibril diameters larger than ~10 nm, the small number of these larger fibrils is not as pronounced in SAXS because SAXS is a numberaveraged method. The similar magnitude between fibril width and height for low MW PII-2T in CB indicates the fibrils have roughly isotropic cross-sections. For low MW PII-2T in Dec, SEM imaging shows two types of structures featuring large agglomerates consistent with observations by eye and also fibril aggregates with widths of ~10 nm in plane. Likewise, AFM imaging shows fibril agglomeration and fibril aggregates with heights ranging from several nm to ~20 nm. For high MW PII-2T in CB, the SEM and AFM results show clearly increased fiber dimensions with the widths ranging from approximately several 10's of nm to >100 nm and the heights ranging from ~50 to 100 nm in the AFM linecut. This is consistent with the fibril cross-sectional Guinier knee moving out of range below 𝑞 = 0.003 Å -1 that corresponds to fiber diameters of > ~60 nm.