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Intra-and intermolecular ordering greatly impact the electronic and optoelectronic properties of semiconducting polymers. Despite much prior efforts regarding molecular packing, the interrelationship between ordering of alkyl sidechains and conjugated backbones has not been fully detailed. We report here the discovery of a highly ordered alkyl sidechain phase in six representative semiconducting polymers, determined from distinct spectroscopic and diffraction signatures. The sidechain ordering exhibits unusually large coherence lengths of at least 70 nm, induces torsional/twisting backbone disorder, and results in a vertically layered multilayer nanostructure with ordered sidechain layers alternating with disordered backbone layers. Calorimetry and in-situ variable temperature scattering measurements in a model system PBnDT-FTAZ clearly delineate this competition of ordering that prevents the simultaneous long-range order of both moieties. The longrange sidechain ordering can be exploited as a transient state to fabricate PBnDT-FTAZ films with an atypical edge-on texture and 2.5x improved OFET mobility. The observed influence of ordering between the moieties implies that improved molecular design could produce synergistic rather than destructive ordering effects. Given the large sidechain coherence lengths observed, such synergistic ordering should greatly improve the coherence length of backbone ordering and thereby improve electronic and optoelectronic properties such as charge transport and exciton diffusion lengths.

We report the use of infrared (IR) scattering-type scanning near-field optical microscopy (s-SNOM) as a nondestructive method to map free-carriers in axially modulation-doped silicon nanowires (SiNWs) with nanoscale spatial resolution. Using this technique, we can detect local changes in the electrically active doping concentration based on the infrared free-carrier response in SiNWs grown using the vapor-liquid-solid (VLS) method. We demonstrate that IR s-SNOM is sensitive to both p-type and n-type free-carriers for carrier densities above ∼1 × 10 cm. We also resolve subtle changes in local conductivity properties, which can be correlated with growth conditions and surface effects. The use of s-SNOM is especially valuable in low mobility materials such as boron-doped p-type SiNWs, where optimization of growth has been difficult to achieve due to the lack of information on dopant distribution and junction properties. s-SNOM can be widely employed for the nondestructive characterization of nanostructured material synthesis and local electronic properties without the need for contacts or inert atmosphere.

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