  A new class of donor-acceptor (D-A) copolymers found to produce high charge
carrier mobilities competitive with amorphous silicon ($> 1
cm^{2}V^{-1}s^{-1}$) exhibits the puzzling microstructure of substantial local
order, however lacking long-range order and crystallinity previously deemed
necessary for achieving high mobility. Here, we demonstrate the application of
low-dose transmission electron microscopy to image and quantify the nanoscale
and mesoscale organization of an archetypal D-A copolymer across areas
comparable to electronic devices (~ $9 {\mu}m^{2}$). The local structure is
spatially resolved by mapping the backbone (001) spacing reflection, revealing
nanocrystallites of aligned polymer chains over nearly the entire film.
Analysis of the nanoscale structure of its ordered domains suggests significant
short- and medium-range order and preferential grain boundary orientations.
Moreover, we provide insights into the rich, interconnected mesoscale
organization of this new family of D-A copolymers by analysis of the local
orientational spatial autocorrelations.
