Figure 1

AFM height and phase images of pure PBTTT spin cast, slow-dried and drop-cast height.
The height and phase scales are: 0–15 nm and 0–15 deg. for PBTTT spin-cast, 0–30 nm and 0–20 deg. for slow-dried and 0–30 nm and 0–20 deg. for drop-cast. The film thickness is approximately 60 ± 10 nm for all the pure polymer samples (measured by profilometer). None of the pure PBTTT films were thermally annealed.