Tuning conformation, assembly, and charge transport properties of conjugated polymers by printing flow

Abstract

Intrachain charge transport is unique to conjugated polymers distinct from inorganic and small molecular semiconductors and is key to achieving high-performance organic electronics. Polymer backbone planarity and thin film morphology sensitively modulate intrachain charge transport. However, simple, generic nonsynthetic approaches for tuning backbone planarity and the ensuing multiscale assembly process do not exist. We first demonstrate that printing flow is capable of planarizing the originally twisted polymer backbone to substantially increase the conjugation length. This conformation change leads to a marked morphological transition from chiral, twinned domains to achiral, highly aligned morphology, hence a fourfold increase in charge carrier mobilities. We found a surprising mechanism that flow extinguishes a lyotropic twist-bend mesophase upon backbone planarization, leading to the observed morphology and electronic structure transitions.

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.…”

Achieving High Alignment of Conjugated Polymers by Controlled Dip‐Coating

“…In addition, Raman spectroscopy showed a blue shift about 5 cm −1 of the peak at 1445 and 1350 cm −1 . [ 32 ] The relative distance and intensity of these two peaks grew similar as the coating speed increased (Figure S2C, Supporting Information). We infer that the films aligned at higher coating speed (≥5 µm s −1 ) might exhibit more planar backbones [ 38 ] while the planarization is also a prominent feature in the transition regime.…”

“…The transition regime leads to the molecular scale planarization of the polymer backbone, and benefits the ensuing multiscale alignment of aggregates (Figure 1D). [ 32 ] The transition regime occurs at a coating speed which is related to a variety of factors like temperature, solvent, concentration, material, and atmosphere. [ 28,33 ] We propose the molecular conformation change is essentially independent on the concentration if the concentration is within a small range.…”

“…We infer that the films aligned at higher coating speed (≥5 µm s −1 ) might exhibit more planar backbones [ 38 ] while the planarization is also a prominent feature in the transition regime. [ 32 ]…”

“…However, in the dilute solution, the disordered aggregates contribute to the tilted out‐of‐plane orientation. [ 32 ] The lack of the in‐plane π‐stacking peaks in both directions may be attributed to the disordered lamellar packing along the coating direction. We also observed sharp and intense peaks perpendicular to the coating direction while tilted peaks with arcs of diffraction intensity along the coating direction.…”