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This work resolves the inter- and intramolecular polarized absorption of polarons in the organic semiconductor P3HT, allowing previous theoretical predictions to be tested. Vibronic coupling is shown to be crucial in understanding polaron absorption. 

A grand challenge in materials science is to identify the impact of molecular composition and structure across a range of length scales on macroscopic properties. We demonstrate a unified experimental–theoretical framework that coordinates experimental measurements of mesoscale structure with molecular-level physical modeling to bridge multiple scales of physical behavior. Here we apply this framework to understand charge transport in a semiconducting polymer. Spatially-resolved nanodiffraction in a transmission electron microscope is combined with a self-consistent framework of the polymer chain statistics to yield a detailed picture of the polymer microstructure ranging from the molecular to device relevant scale. Using these data as inputs for charge transport calculations, the combined multiscale approach highlights the underrepresented role of defects in existing transport models. Short-range transport is shown to be more chaotic than is often pictured, with the drift velocity accounting for a small portion of overall charge motion. Local transport is sensitive to the alignment and geometry of polymer chains. At longer length scales, large domains and gradual grain boundaries funnel charges preferentially to certain regions, creating inhomogeneous charge distributions. While alignment generally improves mobility, these funneling effects negatively impact mobility. The microstructure is modified in silico to explore possible design rules, showing chain stiffness and alignment to be beneficial while local homogeneity has no positive effect. This combined approach creates a flexible and extensible pipeline for analyzing multiscale functional properties and a general strategy for extending the accesible length scales of experimental and theoretical probes by harnessing their combined strengths. 

Abstract π‐conjugated polymers (CPs) that are concurrently soft and stretchable are needed for deformable electronics. Molecular‐level modification of indacenodithiophene (IDT) copolymers, a class of CPs that exhibit high hole mobilities (_hole), is an approach that can help realize intrinsically soft and stretchable CPs. Numerous examples of design strategies to adjust the stretchability of CPs exist, but imparting softness is comparatively less studied. In this study, a systematic molecular weight (MW) series is constructed on a promising candidate for soft CPs, poly(indacenodithiophene‐co‐thienopyrroledione) (p(IDT_C16‐TPD_C8)), by optimizing direct arylation polymerization conditions in hopes of improving stretchability andμ_holewithout significantly impacting softness. We found p(IDT_C16‐TPD_C8) at a degree of polymerization of 32 shows high stretchability (crack onset strain,CoS> 100%) without significantly impacting softness (elastic modulus,E= 32 MPa), which to the best of our knowledge outperforms previously reported stretchable and soft CPs. To further study how molecular‐level modifications impact polymer properties, a MW series of a new extended donor unit polymer, poly(indacenodithienothiophene‐co‐thienopyrroledione) (p(IDTT_C16‐TPD_C8)), was synthesized. The IDTT_C16copolymers did not result in a greater averageμ_holewhen comparing between p(IDTT_C16‐TPD_C8) and p(IDT_C16‐TPD_C8) despite their higher crystallinity observed by GIWAXS. While these findings warrant further investigation, this study points toward unique charge transport properties of IDT‐based polymers. 

The ability to control the charge density of organic mixed ionic electronic conductors (OMIECs) via reactions with redox-active analytes has enabled applications as electrochemical redox sensors. Their charge density-dependent conductivity can additionally be tuned via charge injection from electrodes, for instance in organic electrochemical transistors (OECTs), where volumetric charging of the OMIEC channel enables excellent transconductance and amplification of low potentials. Recent efforts have combined the chemical detection with the transistor function of OECTs to achieve compact electrochemical sensors. However, these sensors often fall short of the expected amplification performance of OECTs. Here, we investigate the operation mechanism of various OECT architectures to deduce the design principles required to achieve reliable chemical detection and signal amplification. By utilizing a non-polarizable gate electrode and conducting the chemical reaction in a compartment separate from the OECT, the recently developed Reaction Cell OECT achieves reliable modulation of the OECT channel's charge density. This work demonstrates that systematic and rational design of OECT chemical sensors requires understanding the electrochemical processes that result in changes in the potential (charge density) of the channel, the underlying phenomenon behind amplification.