No 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.

Donor−acceptor (D-A) conjugated polymers are high-performance organic electronic materials that exhibit complex aggregation behavior. Understanding the solution state conformation and aggregation of conjugated polymers is crucial for controlling morphology during thin-film deposition and the subsequent electronic performance. However, a precise multiscale structure of solution state aggregates is lacking. Here, we present an in-depth small-angle X-ray scattering (SAXS) analysis of the solution state structure of an isoindigo-bithiophene-based D-A polymer (PII-2T) in chlorobenzene and decane as our primary system. Modeling the system as a combination of hierarchical fibrillar aggregates mixed with dispersed polymers, we extract information about conformation and multiscale aggregation and also clarify the physical origin of features often observed but unaddressed or misinterpreted in small-angle scattering patterns of conjugated polymers. The persistence length of the D-A polymer extracted from SAXS agrees well with a theoretical model based on the dihedral potentials. Additionally, we show that the broad high q structure factor peak seen in scattering profiles can be attributed to lamellar stacking occurring within the fibril aggregates and that the low q aggregate scattering is strongly influenced by the polymer molecular weight. Overall, the SAXS profiles of D-A polymers in general exhibit a sensitive dependence on the co-existence of fibrillar aggregate and dispersed polymer chain populations. We corroborate our findings from SAXS with electron microscopy of freeze-dried samples for direct imaging of fibrillar aggregates. Finally, we demonstrate the generality of our approach by fitting the scattering profiles of a variety of D-A polymers based on thieno-isoindigo (PTII-2T), diketopyrrolopyrrole (DPP2T-TT, DPP-BTZ, PDPP2FT-C 16 ), naphthalenediimide (P(NDI2OD-T2)), and a conjugated block copolymer P3HT-b-DPPT-T. The results presented here establish a picture of the D-A polymer solution state structure and provide a general method of interpreting and analyzing their scattering profiles.

We compare two small π-conjugated donor–bridge–acceptor organic molecules with the aim of rationalizing the origin for the enhancement in singlet exciton diffusion coefficient and length in 1 with respect to 2.

The design of semiconducting polymers with optimal charge transport characteristics has been at the crux of scientific research during the recent decades. While increase in crystalline order and planar conjugated backbones were demonstrated to be the key to success, they are not always mandatory. Sometimes, the charge carrier mobility can be enhanced by selecting conjugated backbones that are resilient to thermal fluctuations, despite leading to poor structural order. Herein, by coupling all-atom molecular dynamics simulations, electronic structure calculations, and kinetic Monte Carlo charge transport simulations, we demonstrate that the charge carrier mobility in amorphous donor–acceptor conjugated polymers is controlled by the density and quality of close-contact points between the chains and that the latter varies with the size of the donor block and the resulting alkyl side-chain density. We show an application of this strategy to the high-mobility poly­(indaceno­dithiophene-alt-benzothiadiazole) (IDTBT) and poly­(dithiophene­indenofluorene-alt-benzothiadiazole) (TIFBT) copolymers.