Not All Aggregates Are Made the Same: Distinct Structures of Solution Aggregates Drastically Modulate Assembly Pathways, Morphology, and Electronic Properties of Conjugated Polymers

Assessing amyloid fibrils and amorphous aggregates: A review

Protein misfolding and aggregation play a central role in the progression of neurodegenerative diseases such as Alzheimer's and Parkinson's. These aggregates manifest either as structured amyloid fibrils enriched in β-sheet conformations or as irregular amorphous aggregates with diverse morphologies. Understanding their formation, structure, and behavior is critical for deciphering disease mechanisms and developing targeted diagnostics and therapeutics. This review presents an integrated overview of both conventional and advanced techniques used to detect, distinguish, and structurally characterize these protein aggregates. It covers a range of spectroscopic and spectrometric tools, such as fluorescence, Raman, and mass spectrometry that facilitate aggregate identification. Microscopy methods, including atomic force and electron microscopy, are highlighted for morphological analysis. The review also discusses in situ detection strategies using fluorescent dyes, conformation-specific antibodies, enzymatic reporters, and real-time imaging. Separation methods like centrifugation, electrophoresis, and chromatography are outlined alongside structural analysis tools such as X-ray diffraction. Furthermore, the growing utility of computational approaches and artificial intelligence in predicting aggregation propensities and integrating biological data is emphasized. By critically evaluating each method's capabilities and limitations, this review provides a practical and forward-looking resource for researchers studying the complex landscape of protein aggregation.

Lyotropic Liquid Crystal Mediated Assembly of Donor Polymers Enhances Efficiency and Stability of Blade-Coated Organic Solar Cells

Conjugated polymers can undergo complex, concentration-dependent self-assembly during solution processing, yet little is known about its impact on film morphology and device performance of organic solar cells. Herein, lyotropic liquid crystal (LLC) mediated assembly across multiple conjugated polymers is reported, which generally gives rise to improved device performance of blade-coated non-fullerene bulk heterojunction solar cells. Using D18 as a model system, the formation mechanism of LLC is unveiled employing solution X-ray scattering and microscopic imaging tools: D18 first aggregates into semicrystalline nanofibers, then assemble into achiral nematic LLC which goes through symmetry breaking to yield a chiral twist-bent LLC. The assembly pathway is driven by increasing solution concentration - a common driving force during evaporative assembly relevant to scalable manufacturing. This assembly pathway can be largely modulated by coating regimes to give 1) lyotropic liquid crystalline assembly in the evaporation regime and 2) random fiber aggregation pathway in the Landau-Levich regime. The chiral liquid crystalline assembly pathway resulted in films with crystallinity 2.63 times that of films from the random fiber aggregation pathway, significantly enhancing the T80 lifetime by 50-fold. The generality of LLC-mediated assembly and enhanced device performance is further validated using polythiophene and quinoxaline-based donor polymers.

Recent Advances in Polymorphism of Organic Solar Cells

As organic solar cells (OSCs) achieve notable advancements, a significant consensus has been highlighted that the device performance is intricately linked to the active layer morphology. With conjugated molecules being widely employed, intermolecular interactions exert substantial influence over the aggregation state and morphology formation, resulting in distinct molecular packing motifs, also known as polymorphism. This phenomenon is closely associated with processing conditions and exerts a profound impact on functional properties. Consequently, understanding the mechanisms underlying polymorphism formation and establishing a definitive correlation between polymorphism and photophysical behavior is crucial for driving high-performance OSCs. In this review, a comprehensive synthesis of recent developments is provided and emphasizing its pivotal role in the field of OSC polymorphism. The thermodynamic and kinetic principles governing polymorphism formation are examined. Then, representative polymorphisms are classified in OSC materials, segmenting them into homopolymers, copolymers, and IDTT- and BTP-based small molecules. Additionally, prevalent strategies are evaluated for manipulating polymorphism. This review culminates with an analysis of the critical effects of polymorphism on OSCs, including charge carrier characteristics, photovoltaic efficiency, and long-term stability. By offering novel perspectives and practical insights, this work seeks to guide future efforts in the morphological optimization of high-efficiency OSCs.

Unveiling emissive H-aggregates of benzocoronenediimide, their photophysics and ultrafast exciton dynamics

H- and J-aggregates of many molecules can be considered ordered mesoscopic structures that behave like a single entity. This is due to coherent electronic coupling between electronic excitations of aggregated molecules, resulting in distinct electronic properties compared to the monomer. H-aggregates are generally non-emissive and, due to this property, they are considered unfit for optoelectronics applications, but they have found applications in organic light-emitting transistors. Herein, we designed t-butyl-substituted benzocoronenediimide (t-But-BCDI) forming rare emissive H-aggregates. The tertiary butyl groups are placed to inhibit the formation of strong aggregates. Photophysical studies showed that t-But-BCDI forms H-aggregates in a concentrated solution in a THF/CHCl3 mixture. A blue shift in absorption along with a decrease in the A0-0/A0-1 ratio and red-shifted weaker emission are observed for the aggregate compared to the monomer. Ultrafast transient absorption studies revealed biphasic relaxation with lifetimes of 150 (±10) fs and 13 (±2) ps, which are attributed to a higher-to-lower state transition and vibrational cooling, respectively. The transient spectral signature suggests the Frenkel-type (localized to a monomer) character of the exciton. Faster evolution at the tens of picosecond timescale suggests relaxation of the exciton state within the H-type exciton band. An extraordinarily long emission lifetime from the H-aggregated state is observed.

Manipulating Backbone Planarity of Ester Functionalized Conjugated Polymer Constitutional Isomer Derivatives Blended with Molecular Acceptors for Controlling Photovoltaic Properties

Exploring both electron donor and acceptor phase components in bulk heterojunction structures has contributed to the advancement of organic photovoltaics (OPV) realizing power conversion efficiencies reaching 20%. Being able to control backbone planarity of the donor polymer, while understanding its effects on the polymer conformation and photophysical properties, fosters the groundwork for further achievements in this realm. In this report, three isomeric PM7 derivatives are designed and synthesized where the benzodithiophene-4,8-dione structure is replaced by a quaterthiophene bridge carrying two ester moieties. The placement of these two ester groups varies among three configurational isomers, which ultimately influences the chain conformations and aggregation behavior of each polymer. Specifically, PM7-D3 has ester groups attached to the inner positions of the outer thiophenes showing moderate solution aggregation; PM7-D4 has ester groups attached to the inner positions of the inner thiophenes featuring a twisted backbone with no solution aggregation behavior; and PM7-D5 has ester groups attached to the outer positions of the inner thiophenes with strong solution aggregation. PM7-D5 shows the highest average power conversion efficiency of 11.4% paired with the molecular acceptor L8-BO. In addition, the differences among the polymer backbones are expressed by their state energies and carrier mobility in the corresponding fabricated OPV devices.

Integrated Materials Design and Process Engineering for n-Type Polymer Thermoelectrics

Polymer thermoelectrics (TEs) have attracted increasing interest in recent years, owing to their great potential in intimate integration with wearable electronics for powering small electronics/sensors and personal temperature regulation. Over the past few decades, substantial progress has been made in enhancing polymer TE performance. However, the electrical conductivity and power factor of most n-doped polymers are about an order of magnitude lower than those of their p-type counterparts, impeding the development of highly efficient polymer TE devices. In addition, unlike well-studied inorganic materials, the complex charge transport mechanism and polymer-dopant interactions in polymer TE materials have hindered a comprehensive understanding of the structure-property relationships. This Perspective aims to survey recent achievements in understanding the charge transport mechanism and selectively provide some critical insights into molecular design and process engineering for n-type polymer TEs. We also highlight the great potential of polymer TEs in wearable electronics and offer an outlook for future development.

Increasing the Content of Edge-On Orientation to Improve the Hole Mobility of IDTBT Film by the van der Waals Interaction between the Side Chain and Alkane Additives

The molecular orientation in the conjugated polymer film critically impacts the performance of organic electronic devices. As for organic field-effect transistors (OFETs), the edge-on orientation is beneficial for efficient interchain charge transport. However, for the near amorphous indacenodithiophene-co-benzothiadiazole (IDTBT) film, the face-on orientation was dominated in the drop cast thin film. Herein, we proposed a strategy to increase the edge-on orientation in IDTBT films by inserting n-hexadecane (16C) additives with a high boiling point between the side chains. Because the 16C additives had a similar structure to that of the side chain, the 16C additives were distributed around the side chain in the nucleation stage. Then, the backbone aggregated quickly with the nuclei formation speed (k) nearly twice as high as that without the 16C additives. In the growth stage, some face-on nuclei turned to edge-on nuclei due to the van der Waals interactions between the side chain and 16C additives. This was verified by the results of in situ GIWAXS, where the intensity of (010) decreased and the intensity of (100) increased in the out-of-plane direction. The edge-on orientation content of the film with 16C additives reached 57%, higher than that of the neat film (33%). Moreover, compared to the neat IDTBT film, the lamellar packing distance of the film with 16C additives increased the lamellar packing distance from 16.97 to 23.26 Å and the π-π stacking distance decreased from 4.36 to 4.19 Å. The hole mobility of the film with 16C additives (3.24 ± 0.19 cm2 V-1 s-1) was higher than that of the neat film (0.94 ± 0.07 cm2 V-1 s-1).

Soft hydrogel semiconductors with augmented biointeractive functions

Hydrogels, known for their mechanical and chemical similarity to biological tissues, are widely used in biotechnologies, whereas semiconductors provide advanced electronic and optoelectronic functionalities such as signal amplification, sensing, and photomodulation. Combining semiconducting properties with hydrogel designs can enhance biointeractive functions and intimacy at biointerfaces, but this is challenging owing to the low hydrophilicity of polymer semiconductors. We developed a solvent affinity-induced assembly method that incorporates water-insoluble polymer semiconductors into double-network hydrogels. These semiconductors exhibited tissue-level moduli as soft as 81 kilopascals, stretchability of 150% strain, and charge-carrier mobility up to 1.4 square centimeters per volt per second. When they are interfaced with biological tissues, their tissue-level modulus enables alleviated immune reactions. The hydrogel's high porosity enhances molecular interactions at semiconductor-biofluid interfaces, resulting in photomodulation with higher response and volumetric biosensing with higher sensitivity.

Unraveling the Solution Aggregation Structures and Processing Resiliency of High-Efficiency Organic Photovoltaic Blends

The solution aggregation structure of conjugated polymers is crucial to the morphology and resultant optoelectronic properties of organic electronics and is of considerable interest in the field. Precise characterizations of the solution aggregation structures of organic photovoltaic (OPV) blends and their temperature-dependent variations remain challenging. In this work, the temperature-dependent solution aggregation structures of three representative high-efficiency OPV blends using small-angle X-ray/neutron scattering are systematically probed. Three cases of solution processing resiliency are elucidated in state-of-the-art OPV blends. The exceptional processing resiliency of high-efficiency PBQx-TF blends can be attributed to the minimal changes in the multiscale solution aggregation structure at elevated temperatures. Importantly, a new parameter, the percentage of acceptors distributed within polymer aggregates (Ф), for the first time in OPV blend solution, establishes a direct correlation between Ф and performance is quantified. The device performance is well correlated with the Kuhn length of the cylinder related to polymer aggregates L1 at the small scale and the Ф at the large scale. Optimal device performance is achieved with L1 at ≈30 nm and Ф within the range of 60 ± 5%. This study represents a significant advancement in the aggregation structure research of organic electronics.

Current State and Future Perspectives of Printable Organic and Perovskite Solar Cells

Photovoltaic technology presents a sustainable solution to address the escalating global energy consumption and a reliable strategy for achieving net-zero carbon emissions by 2050. Emerging photovoltaic technologies, especially the printable organic and perovskite solar cells, have attracted extensive attention due to their rapidly transcending power conversion efficiencies and facile processability, providing great potential to revolutionize the global photovoltaic market. To accelerate these technologies to translate from the laboratory scale to the industrial level, it is critical to develop well-defined and scalable protocols to deposit high-quality thin films of photoactive and charge-transporting materials. Herein, the current state of printable organic and perovskite solar cells is summarized and the view regarding the challenges and prospects toward their commercialization is shared. Different printing techniques are first introduced to provide a correlation between material properties and printing mechanisms, and the optimization of ink formulation and film-formation during large-area deposition of different functional layers in devices are then discussed. Engineering perspectives are also discussed to analyze the criteria for module design. Finally, perspectives are provided regarding the future development of these solar cells toward practical commercialization. It is believed that this perspective will provide insight into the development of printable solar cells and other electronic devices.

Effect of solvent quality and sidechain architecture on conjugated polymer chain conformation in solution

Conjugated polymers (CPs) are solution-processible for various electronic applications, where solution aggregation and dynamics could impact the morphology in the solid state. Various solvents and solvent mixtures have been used to dissolve and process CPs, but few studies have quantified the effect of solvent quality on the solution behavior of CPs. Herein, we performed static light scattering and small-angle X-ray scattering combined with molecular dynamics (MD) simulation to investigate CP solution behaviors with solvents of varying quality, including poly(3-alkylthiophene) (P3ATs) with various sidechain lengths from -C4H9 to -C12H25, poly[bis(3-dodecyl-2-thienyl)-2,2'-dithiophene-5,5'-diyl] (PQT-12) and poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-12). We found that chlorobenzene is a better solvent than toluene for various CPs, which was evident from the positive second virial coefficient A2 ranging from 0.3 to 4.7 × 10-3 cm3 mol g-2 towards P3ATs. For P3ATs in non-polar solvents, longer sidechains promote more positive A2, indicating a better polymer-solvent interaction, wherein A2 for toluene increases from -5.9 to 1.4 × 10-3 cm3 mol g-2, and in CB, A2 ranges from 1.0 to 4.7 × 10-3 cm3 mol g-2 when sidechain length increases from -C6H13 to -C12H25. Moreover, PQT-12 and PBTTT-12 have strong aggregation tendencies in all solutions, with an apparent positive A2 (∼0.5 × 10-3 cm3 mol g-2) due to multi-chain aggregates and peculiar chain folding. These solvent-dependent aggregation behaviors can be well correlated to spectroscopy measurement results. Our coarse-grained MD simulation results further suggested that CPs with long, dense, and branched sidechains can achieve enhanced polymer-solvent interaction, and thus enable overall better solution dispersion. This work provides quantitative insights into the solution behavior of conjugated polymers that can guide both the design and process of CPs toward next-generation organic electronics.

Subtle Molecular Changes Largely Modulate Chiral Helical Assemblies of Achiral Conjugated Polymers by Tuning Solution-State Aggregation

Understanding the solution-state aggregate structure and the consequent hierarchical assembly of conjugated polymers is crucial for controlling multiscale morphologies during solid thin-film deposition and the resultant electronic properties. However, it remains challenging to comprehend detailed solution aggregate structures of conjugated polymers, let alone their chiral assembly due to the complex aggregation behavior. Herein, we present solution-state aggregate structures and their impact on hierarchical chiral helical assembly using an achiral diketopyrrolopyrrole-quaterthiophene (DPP-T4) copolymer and its two close structural analogues wherein the bithiophene is functionalized with methyl groups (DPP-T2M2) or fluorine atoms (DPP-T2F2). Combining in-depth small-angle X-ray scattering analysis with various microscopic solution imaging techniques, we find distinct aggregate in each DPP solution: (i) semicrystalline 1D fiber aggregates of DPP-T2F2 with a strongly bound internal structure, (ii) semicrystalline 1D fiber aggregates of DPP-T2M2 with a weakly bound internal structure, and (iii) highly crystalline 2D sheet aggregates of DPP-T4. These nanoscopic aggregates develop into lyotropic chiral helical liquid crystal (LC) mesophases at high solution concentrations. Intriguingly, the dimensionality of solution aggregates largely modulates hierarchical chiral helical pitches across nanoscopic to micrometer scales, with the more rigid 2D sheet aggregate of DPP-T4 creating much larger pitch length than the more flexible 1D fiber aggregates. Combining relatively small helical pitch with long-range order, the striped twist-bent mesophase of DPP-T2F2 composed of highly ordered, more rigid 1D fiber aggregate exhibits an anisotropic dissymmetry factor (g-factor) as high as 0.09. This study can be a prominent addition to our knowledge on a solution-state hierarchical assembly of conjugated polymers and, in particular, chiral helical assembly of achiral organic semiconductors that can catalyze an emerging field of chiral (opto)electronics.

Conjugated Polymer Process Ontology and Experimental Data Repository for Organic Field-Effect Transistors

Polymer-based semiconductors and organic electronics encapsulate a significant research thrust for informatics-driven materials development. However, device measurements are described by a complex array of design and parameter choices, many of which are sparsely reported. For example, the mobility of a polymer-based organic field-effect transistor (OFET) may vary by several orders of magnitude for a given polymer as a plethora of parameters related to solution processing, interface design/surface treatment, thin-film deposition, postprocessing, and measurement settings have a profound effect on the value of the final measurement. Incomplete contextual, experimental details hamper the availability of reusable data applicable for data-driven optimization, modeling (e.g., machine learning), and analysis of new organic devices. To curate organic device databases that contain reproducible and findable, accessible, interoperable, and reusable (FAIR) experimental data records, data ontologies that fully describe sample provenance and process history are required. However, standards for generating such process ontologies are not widely adopted for experimental materials domains. In this work, we design and implement an object-relational database for storing experimental records of OFETs. A data structure is generated by drawing on an international standard for batch process control (ISA-88) to facilitate the design. We then mobilize these representative data records, curated from the literature and laboratory experiments, to enable data-driven learning of process-structure-property relationships. The work presented herein opens the door for the broader adoption of data management practices and design standards for both the organic electronics and the wider materials community.

Spark Discharge Doping-Achieving Unprecedented Control over Aggregate Fraction and Backbone Ordering in Poly(3-hexylthiophene) Solutions

The properties of semiconducting polymers are strongly influenced by their aggregation behavior, that is, their aggregate fraction and backbone planarity. However, tuning these properties, particularly the backbone planarity, is challenging. This work introduces a novel solution treatment to precisely control the aggregation of semiconducting polymers, namely current-induced doping (CID). It utilizes spark discharges between two electrodes immersed in a polymer solution to create strong electrical currents resulting in temporary doping of the polymer. Rapid doping-induced aggregation occurs upon every treatment step for the semiconducting model-polymer poly(3-hexylthiophene). Therefore, the aggregate fraction in solution can be precisely tuned up to a maximum value determined by the solubility of the doped state. A qualitative model for the dependences of the achievable aggregate fraction on the CID treatment strength and various solution parameters is presented. Moreover, the CID treatment can yield an extraordinarily high quality of backbone order and planarization, expressed in UV-vis absorption spectroscopy and differential scanning calorimetry measurements. Depending on the selected parameters, an arbitrarily lower backbone order can be chosen using the CID treatment, allowing for maximum control of aggregation. This method may become an elegant pathway to finely tune aggregation and solid-state morphology for thin-films of semiconducting polymers.

Conjugated Polymers in Solution: A Physical Perspective

Excellent progress has been made in the optoelectronic properties of conjugated polymers by controlling solution-state aggregation. However, due to the wide variety and complex structures of conjugated polymers, it is still challenging to fully understand the complex aggregation process and microstructures both in solution and in the solid state. This Perspective focuses on the chain conformations and the aggregation of conjugated polymers in solution. We discuss the factors in detail which affect solution-state aggregation and microstructures from the perspective of polymer physics in solutions, including chemical structures and environmental conditions. Based on the understanding of multiple interactions of conjugated polymers in solution, strategies to regulate solid-state microstructures and obtain high-performance polymer-based devices from solution-state aggregation are summarized.

Tuning the nanostructure and molecular orientation of high molecular weight diketopyrrolopyrrole-based polymers for high-performance field-effect transistors

As a versatile class of semiconductors, diketopyrrolopyrrole (DPP)-based conjugated polymers are well suited for applications of next-generation plastic electronics because of their excellent and tunable optoelectronic properties via a rational design of chemical structures. However, it remains a challenge to unravel and eventually influence the correlation between their solution-state aggregation and solid-state microstructure. In this contribution, the solution-state aggregation of high molecular weight PDPP3T is effectively enhanced by solvent selectivity, and a fibril-like nanostructure with short-range and long-range order is generated and tuned in thin films. The predominant role of solvent quality on polymer packing orientation is revealed, with an orientational transition from a face-on to an edge-on texture for the same PDPP3T. The resultant edge-on arranged films lead to a significant improvement in charge transport in transistors, and the field-effect hole mobility reaches 2.12 cm² V^-1 s^-1 with a drain current on/off ratio of up to 10⁸. Our findings offer a new strategy for enhancing the device performance of polymer electronic devices.