Polymer semiconductors typically are pi-conjugated macromolecules. First-generation materials are well-studied and well-understood. They are flexible-chain polymers, leading to heterogeneous microstructures comprised of molecularly disordered (“amorphous”) and ordered regions (crystallites/aggregates) as in commodity plastics such as polyethylene, polypropylene, and polyesters. More modern macromolecular semiconductors are, in contrast, comprised of rigid backbones, requiring elaborate side-chain substitutions to render them processable. Because of the backbone rigidity, polymer semiconductor chains do not entangle, supporting a “liquid-crystalline”-like behavior and low long-range coherence. However, this difference is rarely discussed in literature, and classical polymer physics views, developed for flexible-chain polymers, are applied to rationalize the behavior of next-generation materials. Here, we disucss on the example of next-generation semiconductors that they are ribbon-like i.e., “sanidic”. We show that fast calorimetry, enabling measurements with high sensitivity because of ultra-fast scan rates (5,000 C/s), is a highly useful tool to gain understanding of this polymer class, including structural factors across multiple length-scales that affect charge and mass transport, side-chain softening transitions; and minute changes in mass or heat capacity indicating chemical or structural degradation. Favorable interactions between components in plastic solar cell donor:acceptor blends that render the devices stretchable may also be identified. Knowledge gained can be applied to gain insights in non-conjugated materials, such as commodity polymers, inorganic-organic hybrid materials, poly(oxathianethione) derivatives, and beyond. Collectively, our presentation will highlight the power of thermal analysis to understand polymeric species, beyond the identification of melting and glass transitions, only towards better detailed understanding of macromolecules.

Poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) is a conductive water-processable polymer with many important applications in organic electronics, for example it is well known as a thermoelectric material due to its good electrical conductivity and poor thermal conductivity [1]. The electrical conductivity of PEDOT:PSS layers is very diverse and can be changed by changing the processing and post-deposition conditions, e.g. by using different solvent additives, doping or modifying the physical conditions of the layer deposition [1-3]. Nevertheless, the ratio of conductive PEDOT to insulating PSS remains a key factor [4]. Despite many years of intensive research on the relationship between the microstructure and properties of these layers, there are still gaps in our knowledge, especially with respect to the detailed understanding of the charge carrier transport mechanism in organic semiconductor thin films [1-5]. In this work, we investigate the effect of acid doping of PEDOT:PSS thin films on the intrachain and interchain conductivity by further developing our model [4,5]. This model is based on the generalized effective medium theory and uses the percolation theory equation for the electrical conductivity of a mixture of two materials. Here its implementation assumes that the role of the highly conductive material is attributed to the intrachain conductivity of PEDOT and its quantitative contribution is determined based on the optical Drude–Lorentz model. While the weaker interchain conductivity is assumed to originate from the weakly conductive material and is determined based on electrical measurements using the Van der Pauw method and coherent composition-dependent analysis.

Polymers with tailored electrical and magnetic properties are essential for next-generation flexible electronics and sensor technologies. My research focuses on the design and characterization of flexible, electrically conductive organic materials with organic magnetoresistive properties. We developed and analyzed composites of polypyrrole (PPy), polydimethylsiloxane (PDMS), and nickel (Ni) nanoparticles. PDMS provides mechanical flexibility, while PPy and Ni nanoparticles introduce electrical conductivity and magnetoresistive behavior. The composites were incorporated with varying nickel nanoparticles concentrations and characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), confirming uniform nanoparticle dispersion. Electrochemical impedance spectroscopy revealed a direct correlation between nanoparticle density and electrical properties, identifying the optimal composition for enhanced conductivity. The polymer matrix exhibited tunable electrical behavior with temperature-dependent conductivity, making it promising for temperature-sensing applications. Under an external magnetic field, the composites exhibited a magnetoresistance effect, with conductivity changes observed across various frequencies, indicated by equally spaced peaks in the impedance spectra (Refer to the attached figure). These peaks persisted with increased nanoparticle concentrations, although the overall impedance decreased, highlighting the interplay between spin interactions and nanoparticle density. The results highlight the potential of PPy/PDMS-based composites for applications in flexible electronics, magnetic storage, spintronics, and polymer-based sensors. Current work explores alternative conductive polymers and nanoparticle modifications to enhance performance. These findings are novel, with ongoing efforts to publish the results in a peer-reviewed journal. This study demonstrates a promising approach to develop flexible, intelligent materials for next generation magnetoresistive and temperature-sensing technologies

In-plane anisotropic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films, is induced in laterally applied electric fields during their dry-out (solidification). This can achieve an optimal alignment between their anisotropic properties and the field direction, thereby enhancing charge transport characteristics [1,2].
In this study, PEDOT:PSS thin films were deposited on glass substrates using the spin-coating method under different applied electric fields.Four-probe measurements revealed a significant enhancement in anisotropy, demonstrating the strong influence of increasing electric field strength. Figure 1 presents the resistance measurements in perpendicular and parallel directions for samples subjected to 0 V, 10 V, and 30 V.
Furthermore, we observed that an increase in the applied electric field leads to a higher charge density on the thin-film surface. In other words, the applied electric field induces localized conductive regions, creating variations in conductivity across the surface. Conductive atomic force microscopy (C-AFM) was employed to examine the surface morphology, with Figure 2 displaying scanned images of a sample subjected to a 20 V applied field.
Additionally, the effect of thin-film thickness on in-plane anisotropy was investigated, as shown in Figure 3. This analysis provides deeper insight into charge transport behavior across different film thicknesses and its impact on anisotropy. Understanding the in-plane anisotropy of PEDOT:PSS thin films enable advancements in material optimization and device applications, contributing to improved performance in flexible electronics, energy systems, and sensing technologies.

Bulk heterojunctions (BHJs) are nanoscale interpenetrating networks of electron-donating and electron-accepting conjugated molecules that are solution-processed to form the active layer in the most efficient organic solar cells.[1] Their nanoscale organization, dictated by deposition parameters such as solvent selection, additives, and annealing conditions, critically influences charge generation and transport.[2] Understanding these effects is essential for improving the efficiency and device stability of the solar cells.

In my talk I will discuss the impact of different post-annealing methods on the nanoscale morphology and solar cell performance of BHJs composed of the polymer donor TPD-3F and small-molecule acceptor IT-4F.[3] Our findings reveal that a solvent vapor annealing (SVA) treatment enhances crystallinity and promotes a more favourable molecular orientation of IT-4F within the BHJ. Compared to the control condition (no annealing), thermal, and vacuum annealing, SVA-treated blends exhibit faster photoluminescence quenching and a reduced recombination, indicating a more efficient exciton dissociation. Consequently, the solar cell power conversion efficiency improves from 11.3% in the control devices to 13.84% with SVA, primarily due to an increase in fill factor from 65% to 76%. Additionally, SVA-treated devices exhibit remarkable stability enhancements, both in shelf life and under continuous illumination.


TPD-3F: Poly[[2,2'-[[4,8-Bis[4-fluoro-5-(2-hexyldecyl)-2-thienyl]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]-2,5-thiophenediyl(5,6-dihydro-5-octyl-4,6-dioxo-4H-thieno[3,4-c]pyrrole-1,3-diyl)-2,5-thiophenediyl]]

IT-4F: 9-Bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2’,3’-d’]-s-indaceno[1,2-b:5,6-b’]dithiophene

Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) is considered a conducting polymer with the biggest prospects in the field of organic (bio)electronics. However, it is necessary to develop new PEDOT (co)polymers with additional properties such as stimuli-responsiveness, functionality and biocompatibility to extend its applications. We report a synthetic pathway towards new 3,4-ethylenedioxythiophene (EDOT) end-functional macromonomers and a new generation of multifunctional PEDOT-block copolymers. The macromonomers were synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization mediated by a tailored EDOT functional RAFT chain transfer agent (CTA). To show the versatility of this approach, three types of EDOT macromonomers with controlled molecular weights were synthesized based on poly(methyl methacrylate) (α-EDOT-PMMA), poly(styrene sulfonate) (α-EDOT-PSS) and poly(N-isopropylacrylamide) (α-EDOT-PNIPAM). Then, the macromonomers were copolymerized with the EDOT monomer via chemical oxidative polymerization to obtain the corresponding new PEDOT-b-PMMA, PEDOT-b-PSS and PEDOT-b-PNIPAM block copolymers. The physicochemical and electrochemical properties of the PEDOT-block copolymers were characterized by FTIR, DSC, TGA, contact angle measurement, UV-Vis-NIR spectroscopy, AFM, TEM, CV and EIS, showing the typical features associated with PEDOT and the phase separation of the block copolymers. The PEDOT-b-PSS block copolymers were studied in an organic electrochemical transistor (OECT) and shown to be comparable with the commercial PEDOT:PSS in terms of transconductance and stability. Furthermore, the PEDOT-b-PNIPAM block copolymers showed a low critical solution temperature (LCST) of around 36.0 °C, above which their resistance increased dramatically. The integration of PEDOT-b-PNIPAM in an OECT allowed the generation of bioelectronic devices with a response to temperature variations from 25 to 45 °C.