Competition between Exceptionally Long‐Range Alkyl Sidechain Ordering and Backbone Ordering in Semiconducting Polymers and Its Impact on Electronic and Optoelectronic Properties

Abstract

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.

Sequential Deposition of Organic Films with Eco‐Compatible Solvents Improves Performance and Enables Over 12%‐Efficiency Nonfullerene Solar Cells

“…In addition to the two aforementioned peaks, higher orders of (100) peak (q=0.67, 1.00 Å -1 ) appear in the Q z direction of LM processed film and similar reflections are observed in the DMA derived film. Note that these (200) and (300) peaks were only observed in the drop-cast FTAZ film from 1,2,4-trichlorobenzene [15] . Obviously, LM and DMA processed FTAZ films are highly ordered, as evidenced by the appearance of periodic (h00) reflections along the Q z axis, which has rarely been observed in spun-cast FTAZ films.…”

“…We select a representative donor-acceptor type conjugated polymer FTAZ [13] as our prototypical system, which has been extensively used as a notable partner for nonfullerene acceptors in BHJ solar cells [14] and is considered a nominally amorphous polymer [15] .…”

The Polymer Physics of Multiscale Charge Transport in Conjugated Systems

“…Hence, the overall charge transport can be improved by enhancing local interchain coupling. The aforementioned backbone planarity is also beneficial to enhancing interchain transport, because the less‐twisted polymer chains can π‐stack more readily and improve the interchain ordering . Side chains, although primarily used as solubilizing groups, can be commonly engineered to modulate the π–π stacking distance to improve local packing .…”

A Reversible Structural Phase Transition by Electrochemically-Driven Ion Injection into a Conjugated Polymer

“…Further, we speculate that the two peaks at Q xy = 0.38 A -1 (unlabeled in Figure 3A) are the result of twisting in the polymer. [42][43][44] Once PB2T-TEG is oxidized at +0.4 V, the out-of- plane (100) spacing significantly increases. At the same time, the glycolated chains lose their crystallinity seen by the disappearance of the h10, h20 and h01 Bragg rods and become less interdigitated as the ions disrupt the side chain interactions.…”