Critical analysis of self-doping and water-soluble n-type organic semiconductors: structures and mechanisms

Self-doping organic semiconductors provide a promising route to avoid instabilities and morphological issues associated with molecular n-type dopants. Structural characterization of a naphthalenetetracarboxylic diimide (NDI) semiconductor covalently bound to an ammonium hydroxide group is presented. The dopant precursor was found to be the product of an unexpected base catalyzed hydrolysis, which was reversible. The reversible hydrolysis had profound consequences on the chemical composition, morphology, and electronic performance of the doped films. In addition, we investigated the degradation mechanism of the quaternary ammonium group and the subsequent doping of NDI. These findings reveal that the products of more than one chemical reaction during processing of films must be considered when utilizing this promising class of water-soluble semiconductors

The Influence of Regiochemistry on the Performance of Organic Mixed Ionic and Electronic Conductors.

Thiophenes functionalised in the 3-position are ubiquitous building blocks for the design and synthesis of organic semiconductors. Their non-centrosymmetric nature has long been used as a powerful synthetic design tool exemplified by the vastly different properties of regiorandom and regioregular poly(3-hexylthiophene) owing to the repulsive head-to-head interactions between neighbouring side chains in the regiorandom polymer. The renewed interest in highly electron-rich 3-alkoxythiophene based polymers for bioelectronic applications opens up new considerations around the regiochemistry of these systems as both the head-to-tail and head-to-head couplings adopt near-planar conformations due to attractive intramolecular S-O interactions. To understand how this increased flexibility in the molecular design can be used advantageously, we explore in detail the geometrical and electronic effects that influence the optical, electrochemical, structural, and electrical properties of a series of six polythiophene derivatives with varying regiochemistry and comonomer composition. We show how the interplay between conformational disorder, backbone coplanarity and polaron distribution affects the mixed ionic-electronic conduction. Ultimately, we use these findings to identify a new conformationally restricted polythiophene derivative for p-type accumulation-mode organic electrochemical transistor applications with performance on par with state-of-the-art mixed conductors evidenced by a μC* product of 267 F V-1  cm-1  s-1

The Influence of Regiochemistry on the Performance of Organic Mixed Ionic and Electronic Conductors

Thiophenes functionalised in the 3‐position are ubiquitous building blocks for the design and synthesis of organic semiconductors. Their non‐centrosymmetric nature has long been used as a powerful synthetic design tool exemplified by the vastly different properties of regiorandom and regioregular poly(3‐hexylthiophene) owing to the repulsive head‐to‐head interactions between neighbouring side chains in the regiorandom polymer. The renewed interest in highly electron‐rich 3‐alkoxythiophene based polymers for bioelectronic applications opens up new considerations around the regiochemistry of these systems as both the head‐to‐tail and head‐to‐head couplings adopt near‐planar conformations due to attractive intramolecular S−O interactions. To understand how this increased flexibility in the molecular design can be used advantageously, we explore in detail the geometrical and electronic effects that influence the optical, electrochemical, structural, and electrical properties of a series of six polythiophene derivatives with varying regiochemistry and comonomer composition. We show how the interplay between conformational disorder, backbone coplanarity and polaron distribution affects the mixed ionic‐electronic conduction. Ultimately, we use these findings to identify a new conformationally restricted polythiophene derivative for p‐type accumulation‐mode organic electrochemical transistor applications with performance on par with state‐of‐the‐art mixed conductors evidenced by a μC* product of 267 F V−1 cm−1 s−1

Peculiar transient behaviors of organic electrochemical transistors governed by ion injection directionality

Abstract Despite the growing interest in dynamic behaviors at the frequency domain, there exist very few studies on molecular orientation-dependent transient responses of organic mixed ionic–electronic conductors. In this research, we investigated the effect of ion injection directionality on transient electrochemical transistor behaviors by developing a model mixed conductor system. Two polymers with similar electrical, ionic, and electrochemical characteristics but distinct backbone planarities and molecular orientations were successfully synthesized by varying the co-monomer unit (2,2’-bithiophene or phenylene) in conjunction with a novel 1,4-dithienylphenylene-based monomer. The comprehensive electrochemical analysis suggests that the molecular orientation affects the length of the ion-drift pathway, which is directly correlated with ion mobility, resulting in peculiar OECT transient responses. These results provide the general insight into molecular orientation-dependent ion movement characteristics as well as high-performance device design principles with fine-tuned transient responses

Interplay between Side Chain Density and Polymer Alignment: Two Competing Strategies for Enhancing the Thermoelectric Performance of P3HT Analogues

Publication status: PublishedA series of polythiophenes with varying side chain density was synthesized, and their electrical and thermoelectric properties were investigated. Aligned and non-aligned thin films of the polymers were characterized in the neutral and chemically doped states. Optical and diffraction measurements revealed an overall lower order in the thin films with lower side chain density, also confirmed using polarized optical experiments on aligned thin films. However, upon doping the non-aligned films, a sixfold increase in electrical conductivity was observed for the polythiophene with the lowest side chain density compared to poly­(3-hexylthiophene) (P3HT). We found that the improvement in conductivity was not due to a larger charge carrier density but an increase in charge carrier mobility after doping with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). On the other hand, doped aligned films did not show the same trend; lower side chain density instead led to a lower conductivity and Seebeck coefficient compared to those for P3HT. This was attributed to the poorer alignment of the polymer thin films with lower side chain density. The study demonstrates that optimizing side chain density is a synthetically simple and effective way to improve electrical conductivity in polythiophene films relevant to thermoelectric applications