  Molecular packing, crystallinity, and texture of semiconducting polymers are
often critical to performance. Although frame-works exist to quantify the
ordering, interpretations are often just qualitative, resulting in imprecise
and liberal use of terminology. Here, we reemphasize the continuity of the
degree of molecular ordering and advocate that a more nuanced and consistent
terminology is used with regards to crystallinity, semicyrstallinity,
paracrystallinity, crystallite/aggregate, and related characteristics. We are
motivated in part by our own imprecise and inconsistent use of terminology and
the need to have a primer or tutorial reference to teach new group members. We
show that a deeper understanding can be achieved by combining grazing-incidence
wide-angle X-ray scattering and differential scanning calorimetry. We classify
a broad range of representative polymers into four proposed categories based on
the quantitative analysis of molecular order based on the paracrystalline
disorder parameter (g). A small database is presented for over 10
representative conjugated and insulating polymers ranging from amorphous to
semicrystalline. Finally, we outline the challenges to rationally design
perfect polymer crystals and propose a new molecular design approach that
envisions conceptual molecular grafting that is akin to strained and unstrained
hetero-epitaxy in classic (compound) semiconductors thin film growth.
