Jochen Vanderspikken

Organic electrochemical transistors (OECTs) enable the transduction of ionic signals into electronic outputs, positioning them as ideal candidates for next-generation sensing and (bio)signal processing applications. Recent years have witnessed the development of various OECT channel materials, affording insights into structural fine-tuning to achieve optimal performance and/or stability. However, homocouplings, commonly present in alternating conjugated polymers, have largely been overlooked. This study investigates the effect of homocoupling on OECT materials by employing two synthesis methods - standard Stille polymerization and an alternative symmetric approach - to create the p-type enhancement-mode benchmark polymer pgBTTT. The impact of homocoupling, and its absence, is studied by comparing the bulk properties of the two polymers and evaluating their respective OECT metrics. The new, homocoupling-free polymer exhibits a notably improved OECT performance (μC*), mainly due to an average 3-fold increase in electronic mobility (μ).

Organic electrochemical transistors (OECTs) enable the transduction of ionic signals into electronic outputs, positioning them as ideal candidates for next-generation sensing and (bio)signal processing applications. Recent years have witnessed the development of various OECT channel materials, affording insights on structural fine-tuning to achieve optimal performance and/or stability. However, homocouplings, commonly present in alternating conjugated polymers, have largely been overlooked. This study investigates the effect of homocoupling on OECT materials by employing two synthesis methods – standard Stille polymerization and an alternative symmetric approach – to create the p-type enhancement-mode benchmark polymer pgBTTT. The impact of homocoupling, and its absence, is studied by comparing the bulk properties of the two polymers and evaluating their respective OECT metrics. The new, homocoupling-free polymer exhibits a notably improved OECT performance (μC*), mainly due to an increase in electronic mobility (μ), which is attributed to both the perfectly alternating structure and its higher molar mass.

Double binary state diagrams of the benchmark semi‐crystalline conjugated polymer PBTTT and its alkoxy derivatives PBTTT‐OR‐R and PBTTT‐(OR) ₂ , mixed with PC ₆₁ BM, are constructed using Rapid Heat‐Cool Differential Scanning Calorimetry and T‐resolved synchrotron X‐Ray Diffraction. The polymerization method is adapted to ensure the absence of homocouplings and obtain reliable state diagrams, supported by Flory‐Huggins calculations. Co‐crystallization always occurs at a 45:55 w/w% polymer:PC ₆₁ BM mixing ratio. All co‐crystals remain stable up to 260‒280 °C in a wide composition range, and for the first time, it is proven that they show incongruent (peritectic) melting. The three state diagrams show one eutectic , i.e., between polymer and co‐crystal in the case of PBTTT and PBTTT‐OR‐R, and between polymer and PC ₆₁ BM for PBTTT‐(OR) ₂ . The latter eutectic beyond 280 °C leads to a reversible “solid‐solid” transformation with the corresponding co‐crystal. Isothermal treatments, at the onset temperature of co‐crystallization during non‐isothermal cooling, show no loss of co‐crystal quality in combination with PC ₆₁ BM perfectioning for fullerene‐rich PBTTT:PC ₆₁ BM and PBTTT‐OR‐R:PC ₆₁ BM mixtures, whereas PBTTT‐(OR) ₂ :PC ₆₁ BM, as well as Stille‐polymerized PBTTT‐OR‐R:PC ₆₁ BM with homocouplings, show suppression of co‐crystallization with the formation of separate crystals of polymer and PC ₆₁ BM. These opposing effects are explained by the state diagrams, showcasing their substantial value in selecting efficient annealing conditions.

Conjugated organic polymers have substantial potential for multiple applications but their properties are strongly influenced by structural defects such as homocoupling of monomer units and unexpected end-groups. Detecting and/or quantifying these defects requires complex experimental techniques, which hinder the optimization of synthesis protocols and fundamental studies on the influence of structural defects. Mass spectrometry offers a simple way to detect these defects but a manual analysis of many complex spectra is tedious and provides only approximate results. In this work, we develop a computational methodology for analyzing complex mass spectra of organic copolymers. Our method annotates spectra similarly to a human expert and provides quantitative information about the proportions of signal assigned to each ion. Our method is based on the open-source Masserstein algorithm, which we modify to handle large libraries of reference spectra required for annotating complex mass spectra of polymers. We develop a statistical methodology to analyze the quantitative annotations and compare the statistical distributions of structural defects in polymer chains between samples. We apply this methodology to analyze commercial and lab-made samples of a benchmark polymer and show that the samples differ both in the amount and in the types of structural defects.

Ladder-type extension of a push–pull donor polymer affords enhanced peak external quantum efficiencies in microcavity organic photodetectors, with detectivities ranging from 1.07 × 10¹² to 1.82 × 10¹⁰ Jones in the 900–1400 nm regime.

The true structure of alternating conjugated polymers—the state‐of‐the‐art materials for many organic electronics—often deviates from the idealized picture. Homocoupling defects are in fact inherent to the widely used cross‐coupling polymerization methods. Nevertheless, many polymers still perform excellently in the envisaged applications, which raises the question if one should really care about these imperfections. This article looks at the relevance of chemical precision (and lack thereof) in conjugated polymers covering the entire spectrum from the molecular scale, to the micro and mesostructure, up to the device level. The different types of polymerization errors for the alkoxylated variant of the benchmark (semi)crystalline polymer poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene (PBTTT) are identified, visualized, and quantified and a general strategy to avoid homocoupling is introduced. Through a combination of experiments and supported by simulations, it is shown that these coupling defects hinder fullerene intercalation and limit device performance as compared to the homocoupling‐free analog. This clearly demonstrates that structural defects do matter and should be generally avoided, in particular when the geometrical regularity of the polymer is essential. These insights likely go beyond the specific PBTTT derivatives studied here and are of general relevance for the wider organic electronics field.