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Highly performing mixed Sn/Pb-metal halide perovskite solar cells (PSCs) are among the most promising options to reduce Pb content in perovskite devices and enable, owing to their reduced bandgap, the fabrication of all-perovskite tandem solar cells. Whereas pure-Pb perovskite devices exhibit efficiency up to 25.5%, alongside a high open-circuit voltage (asymptotic to 1.2 V), Sn-Pb PSCs still show lower performances (22.2%) due to higher open-circuit voltage losses. Here, we introduced 2,3,4,5,6-pentafluorophenethylammonium cations in a perovskite active layer of composition (FASnI(3))(0.5)(MAPbI(3))(0.5) to obtain highly oriented films with improved thermal stability. The treated films exhibit merged grains with no evidence of 2D structures, which could help to reduce the trap state density at the surface and grain boundaries. Solar cells fabricated with the fluorinated cation added to the active layer displayed reduced trap-assisted recombination losses and lower background carrier density, which leads to enhanced open-circuit voltages with respect to the reference samples and the active layers incorporating unfluorinated phenethylammonium cations. The best device reached an efficiency of 19.13%, with an open-circuit voltage of 0.84 V, which is substantially improved with respect to the reference sample showing 17.47% efficiency and 0.77 V open-circuit voltage. More importantly, the fluorinated cations' addition is instrumental to improve the device's thermal stability; 90.3% of the solar cell initial efficiency is maintained after 90 min of thermal stress at 85 & nbsp;C in a nitrogen atmosphere.& nbsp;Published under an exclusive license by AIP Publishing. We kindly thank A. Kamp and T. Zaharia for the technical support. The author also acknowledge G. H. ten Brink for the kind help with SEM measurements. This work is part of the research program of the Foundation for Fundamental Research on Matter (FOM), which is part of the Netherlands Organization for Scientific Research (NWO). This is a publication of the FOM-focus Group “Next Generation Organic Photovoltaics,” participating in the Dutch Institute for Fundamental Energy Research (DIFFER). The FWO is acknowledged for the funding of research. M.M. is an S.B. Ph.D. fellow at fonds wetenschappelijk onderzoek (FWO) (No. 1S20118N).

Fused-ring core non-fullerene acceptors (NFAs), designated "Y-series", have enabled high-performance organic solar cells (OSCs) achieving over 18% power conversion efficiency (PCE). Since the introduction of these NFAs, much effort has been expended to understand the reasons for their exceptional performance. While several studies have identified key optoelectronic properties that govern high PCEs, little is known about the molecular level origins of large variations in performance, spanning from 5 to 18% PCE, e.g., in the case of PM6:Y6 OSCs. Here, we introduce a combined solid-state NMR, crystallography, and molecular modelling approach to elucidate the atomic-scale interactions in Y6 crystals, thin films, and PM6:Y6 bulk heterojunction (BHJ) blends. We show the Y6 morphologies in BHJ blends are not governed by the morphology in neat films or single crystals. Notably, PM6:Y6 blends processed from different solvents self-assemble into different structures and morphologies, whereby the relative orientations of the sidechains and end groups of the Y6 molecules to their fused-ring cores play a crucial role in determining the resulting morphology and overall performance of the solar cells. The molecular-level understanding of BHJs enabled by this approach will guide the engineering of next-generation NFAs for stable and efficient OSCs. This article is protected by copyright. All rights reserved.

Multi-component systems often display convoluted behavior, pathway complexity and coupled equilibria. In recent years, several ways to control complex systems by manipulating the subtle balances of interaction energies between the individual components have been explored and thereby shifting the equilibrium between different aggregate states. Here we show the enantioselective chain-capping and dilution-induced supramolecular polymerization with a Zn2+-porphyrin-based supramolecular system when going from long, highly cooperative supramolecular polymers to short, disordered aggregates by adding a monotopic Mn3+-porphyrin monomer. When mixing the zinc and manganese centered monomers, the Mn3+-porphyrins act as chain-cappers for Zn2+-porphyrin supramolecular polymers, effectively hindering growth of the copolymer and reducing the length. Upon dilution, the interaction between chain-capper and monomers weakens as the equilibria shift and long supramolecular polymers form again. This dynamic modulation of aggregate morphology and length is achieved through enantioselectivity in the aggregation pathways and concentration-sensitive equilibria. All-atom and coarse-grained molecular simulations provide further insights into the mixing of the species and their exchange dynamics. Our combined experimental and theoretical approach allows for precise control of molecular self-assembly and chiral discrimination in complex systems., Controlling multicomponent systems is difficult due to convoluted behavior, pathway complexity, and coupled equilibria. Here the authors showed modulation of aggregate morphology in a zinc porphyrin-based supramolecular system via judicious capping with a manganese porphyrin monomer, in which the monomer’s chirality can influence the supramolecular behavior.

A major societal issue of disposal and environmental pollution is raised by the enormous and fast-growing production of single-use polyethylene terephthalate (PET) bottles, especially in developing countries. To contribute to the problem solution, an original route to recycle PET in the form of value-added environmentally friendly thermoplastic composites with banana fibres (Musa acuminata) has been developed at the laboratory scale. Banana fibres are a so far undervalued by-product of banana crops with great potential as polymer reinforcement. The melt-processing constraints of commercial PET, including used bottles, being incompatible with the thermal stability limits use of natural fibres; PET has been modified with bio-sourced reactants to produce co-polymers with moderate processing temperatures below 200 °C. First, commercial PET were partially glycolyzed with 1.3-propanediol to produce co-oligomers of about 20 repeating units, which were next chain extended with succinic anhydride and post-treated in a very unusual “soft solid state” process at temperatures in the vicinity of the melting point to generate co-polymers with excellent ductility. The molar mass build-up reaction is dominated by esterification of the chain ends and benefits from the addition of succinic anhydride to rebalance the acid-to-hydroxyl end-group ratio. Infra-red spectroscopy and intrinsic viscosity were extensively used to quantify the concentration of chain ends and the average molar mass of the co-polymers at all stages of the process. The best co-polymers are crystallisable, though at slow kinetics, with a Tg of 48 °C and a melting point strongly dependent upon thermal history. The composites show high stiffness (4.8 GPa at 20% fibres), consistent with the excellent dispersion of the fibres and a very high interfacial cohesion. The strong adhesion can be tentatively explained by covalent bonding involving unreacted succinic anhydride in excess during solid stating. A first approach to quantify the sustainable benefits of this PET recycling route, based on a rational eco-selection method, gives promising results since the composites come close to low-end wood materials in terms of the stiffness/embodied energy balance. Moreover, this approach can easily be extended to many other natural fibres. The present study is limited to a proof of concept at the laboratory scale but is encouraging enough to warrant a follow-up study toward scale-up and application development.

The development of fluorinated polymers is considered to have begun in the late 1930s when poly(chlorotrifluoroethylene) (PCTFE) was successfully prepared and high molecular weight poly(tetrafluoroethylene) (PTFE) was discovered (Ameduri [1], Hansen [2], Ameduri and Boutevin [3], Hougham et al. [4], Améduri et al. [5], Aḿduri et al. [6]).

International audience; Efficient drug discovery is based on a concerted effort in optimizing bioactivity and compound properties such as lipophilicity, and is guided by efficiency metrics that reflect both aspects. While conformation–activity relationships and ligand conformational control are known strategies to improve bioactivity, the use of conformer-specific lipophilicities (logp) is much less explored. Here we show how conformer-specific logp values can be obtained from knowledge of the macroscopic logP value, and of the equilibrium constants between the individual species in water and in octanol. This is illustrated with fluorinated amide rotamers, with integration of rotamer 19F NMR signals as a facile, direct method to obtain logp values. The difference between logp and logP optimization is highlighted, giving rise to a novel avenue for lipophilicity control in drug discovery.

Fire resistant coatings have been proven as an efficient way to improve fire safety in three aspects: reducing the Heat Release Rate (HRR), delaying the ignition time and preventing heat transfer. Herein, a SiO2 based polymeric composite coating with a lower thermal conductivity and brilliant fire resistance was developed. Isocyanate and sodium silicate could form the final Si-O-Si network structure by polymerization. Compared to the wood without coating, the coated wood shows a significantly increase in limit oxygen index (LOI), has reached 48.0 vol% in the test. As for the cone calorimetry test, coated wood shows a 55.3% decrease in the first peak Heat Release Rate (pHRR) and the Total Heat Release (THR) obtains fire-resistant standard. After exposed to butane flame for 30 mins, the coated wood could still maintain its structural integrity with only 180℃ on the non-exposed side. The commercial standard test of the coating was also investigated. To better understand what role does the polyurea play in the system, a theoretical calculation was done during the research to discuss the interaction between the silica and polyurea. As a fast brush-formed coating, it exhibits a great potential in the field of fire-resistant materials, and may broaden the application prospects of wood.

Reversible photoresponsive waterborne dispersions can be directly applied in the paint and printing industry and have several potential applications such as in rewritable optical patterns, security labeling, and sensing. However, the synthesis of such dispersions and application as waterborne coatings has rarely been reported. In this work, photoresponsive polymer dispersions containing light-responsive azobenzene were prepared by resin-stabilized emulsion polymerization. The aqueous dispersions consist of core/shell type polymer particles, where the resin forms the shell around the polymer core. The photoresponsive azobenzene was incorporated into the resin shell (azo-in-shell) or polymer core (azo-in-core). Waterborne coatings were easily prepared by applying the dispersions on glass or paperboard. The photoresponsive behavior of the azobenzene in the dispersions and coatings shows fast and reversible isomerization and a similar half-life of the cis-azobenzene regardless of its surrounding matrix in the coating, dispersion, or solution. Optical patterns were reversibly imprinted in the coatings on paperboard, which remain visible for several hours at room temperature and several weeks when stored in the freezer. The water barrier properties of the azobenzene-containing coatings on paperboard were unaffected by the addition of the azobenzene moieties and isomerization state. Our results reveal a class of photoresponsive azobenzene waterborne coatings that can be easily applied on different substrates.

Soft matter containing Ti3C2Tx MXenes exhibits promising potential in electromechanical sensor development. Current systems suffer from a decrease in sensibility up to complete breakdown due to small structural defects that will be generated during their longtime practical service. Various non-covalent hydrogel systems, based on hydrogen bonding and ionic coupling, have been employed to improve their durability related to their repairability. However, Ti3C2Tx MXenes are not stable in those networks, since they will be irreversibly oxidized in high humidity environment during practical application. Here, we report the use of a novel dynamic covalent bond based network – a MXene acrylate vitrimer network (MAVIN) with a low glass transition temperature, which can not only be repaired fast with high efficiency but also protects the MXenes in sensor applications from oxidation under working conditions. In addition, owing to the strong microwave absorptivity of Ti3C2Tx and of the flexible dynamic covalent bond network, a damaged MAVIN sensor can be repaired by microwave radiation with a high healing efficiency of 92.4% within 1 minute, which is as good as the best healing efficiency reported in literature so far but 30 times faster. With stability at a voltage of 3 V and fast healing demonstrated, MAVIN promises potential usage in reliable and sustainable strain sensors.

The fabrication of highly ordered nanostructured surfaces is desirable in supramolecular chemistry and envisaged to bolster advances in heterogeneous catalysis and microelectronic applications. Here, we report on a novel set of alkylated doubleN,N′-bis(n-alkyl)-naphthalenediimides (NDIs) for the functionalization of highly oriented pyrolytic graphite (HOPG) with precise double lamellar morphologies. A detailed analysis of the two-dimensional (2D) self-assembled monolayers by scanning tunneling microscopy (STM) reveals that the structural repeating unit of the double lamellae is tuned precisely by the length of the alkyl chain that is connecting the NDI units. However, the expected odd-even effect is disturbed within the monolayers of a series of homologues. In contrast, a clear odd-even effect is observed for the melting temperatures of the respective bulk materials. Small-angle X-ray scattering reveals that these bulk materials exhibit nanophase-separated lamellar phases with domain spacings that are slightly larger than the repeating units of the double lamellar structures formed on the HOPG surface. The discrepancy is assigned to a partial desorption of the alkyl spacer from the HOPG surface, which becomes more pronounced when increasing its length. Our findings suggest that this lengthening increases the conformational freedom of the molecules on the surface while retaining a double lamellar morphology.

International audience; We describe herein the first examples of six-coordinate CoII single-ion magnets (SIMs) based on the β-diimine Mebik ligand [Mebik = bis(1-methylimidazol-2-yl)ketone]: two mononuclear [CoII(Rbik)2L2] complexes and one mixed-valence {CoIII2CoII}n chain of formulas [CoII(Mebik)(H2O)(dmso)(μ-NC)2CoIII2(μ-2,5-dpp)(CN)6]n·1.4nH2O (3) [L = NCS (1), NCSe (2) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine (3)]. Two bidentate Mebik molecules plus two monodentate N-coordinated pseudohalide groups in cis positions build somewhat distorted octahedral surroundings around the high-spin cobalt(II) ions in 1 and 2. The diamagnetic [CoIII2(μ-2,5-dpp)(CN)8]2− metalloligand coordinates the paramagnetic [CoII(Mebik)(H2O)(dmso)]2+ complex cations in a bis-monodentate fashion to afford neutral zigzag heterobimetallic chains in 3. Ab initio calculations, and cryomagnetic dc (2.0–300 K) and ac (2.0–12 K) measurements as well as EPR spectroscopy for 1–3 show the existence of magnetically isolated high-spin cobalt(II) ions with D values of 59.84–89.90 (1), 66.32–93.90 (2) and 70.40–127.20 cm−1 (3) and field-induced slow relaxation of the magnetization, being thus new examples of SIMs with transversal magnetic anisotropy. The analysis of their relaxation dynamics reveals that the relaxation of the magnetization occurs by the Raman (with values of the n parameter covering the range 6.0–6.8) and direct spin-phonon processes.

International audience; In the present study, three biodegradable block copolymers composed of a poly(ethylene glycol) block and a copolypeptide block with varying compositions of cationic L-lysine (L-Lys) and hydrophobic benzyl-L-glutamate (Bzl-L-Glu) were designed for gene delivery applications. The polypeptides were synthesized by ring opening polymerization (ROP) and after orthogonal deprotection of Boc-L-Lys side chains, the polymer exhibited an amphiphilic character. To bind or encapsulate plasmid DNA (pDNA), different formulations were investigated: a nanoprecipitation and an emulsion technique using various organic solvents as well as an aqueous pH-controlled formulation method. The complex and nanoparticle (NP) formations were monitored by dynamic light scattering (DLS), and pDNA interaction was shown by gel electrophoresis and subsequent controlled release with heparin. The polypeptides were further tested for their cytotoxicity as well as biodegradability. The complexes and NPs presentingthe most promising size distributions and pDNA binding ability were subsequently evaluated for their transfection efficiency in HEK293T cells. The highest transfection efficiencies were obtained with an aqueous formulation of the polypeptide containing the highest L-Lys content and lowest proportion of hydrophobic, helical structures (P1*), which is therefore a promising candidate for efficient gene delivery by biodegradable gene delivery vectors.

Amylose‑sodium stearate (SS) complexes (2, 5 and 8%) in heat-moisture treated potato starch (HPS) were evaluated for their physicochemical properties. Based on the DSC thermograms, the amylose - SS complexes were successfully formed with high thermal stability, indicated by a melt temperature (Tpeak) of ≥ 112 °C for type I and ≥125 °C for type II complexes. Addition of 2% SS resulted in a single endothermal peak of the complexes, while 5 and 8% led to the formation of type I and II complexes with much higher enthalpy (ΔH) values. The XRD curve confirmed that the complexes were successfully formed. The pasting temperature increased from 66 °C for native to 91 °C for HPS145 complexed starch with 5% SS. Furthermore, the swelling power could be largely decreased, and the granular structure preserved. In addition, the inclusion complexation with SS on (HPS) succesfully improved the cook stabiliy.

An in-situ visualisation of the microstructure of a Carbopol gel flowing in a micro-channel is presented. By means of a novel chemical protocol able to stain the solid material units of the gel with a fluorescent molecule we are able to accurately identify the solid/fluid material units advected by the confined microscopic flow. Based on this novel visualisation technique a full statistical description of the distributions of solid–fluid material units in the flow in terms of space and time averages, probability density functions and space–time correlations is reported for the first time.

The control of morphology and microstructure during and after the active layer processing of bulk-heterojunction solar cells is critical to obtain elevated fill factors and overall good device performance. With the recent development of non-fullerene acceptors, wide attention has been paid to improve miscibility, solubility and nanoscale separation by laborious molecular design processes and by the use of additives. Nonetheless, several post-processing strategies can equally contribute to obtain an optimum phase separation and even to an enhanced crystallinity, but their effect on performance and device lifetime of polymer/non-fullerene acceptor solar cells is still unclear. Herein, we report a systematic comparison between different post-processing treatments including thermal annealing (TA), vacuum drying (VD) and solvent vapor annealing (SVA) on the TPD-3F polymer and IT-4F non-fullerene acceptor, comparing their effects on device performance as well as on the morphology and optical and electrical properties. The optimized SVA treated devices exhibited power conversion efficiencies close to 14% with a remarkable 76% fill factor and superior short-circuit currents compared to the one of untreated devices. Moreover, SVA demonstrated improvements in device stability both under illumination and under ambient conditions. The induced phase separation and the increased crystallinity of the acceptor molecules, as revealed by GIWAXS measurements, led to increased photogenerated currents, with a more effective exciton dissociation and charge collection. The open-circuit voltage losses in the SVA and TA devices were explained by a bandgap reduction and a higher trap-assisted recombination, respectively. Overall, our study points to the role of post-processing in organic solar cell fabrication, and contributes towards a new generation of efficient and stable additive-free organic solar cells., Post-processing the active layer in additive-free organic solar cells enabled an enhancement in performance due to an increased acceptor crystallinity, resulting in a fill factor of 76%, a power conversion efficiency of 13.84% and an improved stability.

The extracellular matrix (ECM) forms through hierarchical assembly of small and larger polymeric molecules into a transient, hydrogel-like fibrous network that provides mechanical support and biochemical cues to cells. Synthetic, fibrous supramolecular networks formed via non-covalent assembly of various molecules are therefore potential candidates as synthetic mimics of the natural ECM, provided that functionalization with biochemical cues is effective. Here, combinations of slow and fast exchanging molecules that self-assemble into supramolecular fibers are employed to form transient hydrogel networks with tunable dynamic behavior. Obtained results prove that modulating the ratio between these molecules dictates the extent of dynamic behavior of the hydrogels at both the molecular and the network level, which is proposed to enable effective incorporation of cell-adhesive functionalities in these materials. Excitingly, the dynamic nature of the supramolecular components in this system can be conveniently employed to formulate multicomponent supramolecular hydrogels for easy culturing and encapsulation of single cells, spheroids, and organoids. Importantly, these findings highlight the significance of molecular design and exchange dynamics for the application of supramolecular hydrogels as synthetic ECM mimics.

Vitrimers are a subclass of covalent adaptable networks which introduce reshapeability and recyclability in thermoset materials while maintaining a high degree of chemical resistance and dimensional stability. Vitrimer materials based on vinylogous urethane (VU) chemistry have drawn a lot of attention in this area. Classically, these are obtained by the polycondensation polymerization of acetoacetate and amine monomers. Unfortunately, this also releases water, often leading to porosity defects in the initially obtained non-reprocessed cross-linked materials. Here, we demonstrate that alkyne esters (AE) can be used as alternative building blocks for VU vitrimers by a polyaddition polymerization with amines, leading to water-free formulations and straightforward access to defect-free cured VU vitrimer materials. The bond formation and dynamic bond exchange was also studied by small molecule reactions, further rationalized by a computational (DFT) approach. The resulting water-free VU vitrimers display similar material properties compared to vitrimers based on acetoacetates, although also some differences are seen, which can be related to a minor amide-bond forming side reaction. Furthermore, by use of this novel AE approach, polyaddition curing of VU epoxy vitrimers can easily be prepared in a one-pot three-component method, combining AE, amine, and epoxy monomers. This study shows that AE monomers can be used as an easy drop-in method to obtain processable epoxy materials with tunable viscoelastic properties, where the viscous flow behavior can in principle be fully tuned by varying the monomers' ratios and compositions.

The use of organic photoredox catalysts provides new ways to perform metal-free reactions controlled by light. While these reactions are usually performed in organic media, the application of these catalysts at ambient temperatures in aqueous media is of considerable interest. We here compare the activity of two established organic photoredox catalysts, one based on 10-phenylphenothiazine (PTH) and one based on an acridinium dye (ACR), in the light-activated dehalogenation of aromatic halides in pure water. Both PTH and ACR were covalently attached to amphiphilic polymers that are designed to form polymeric nanoparticles with hydrodynamic diameter DH ranging between 5 and 11 nm in aqueous solution. Due to the hydrophobic side groups that furnish the interior of these nanoparticles after hydrophobic collapse, water-insoluble reagents can gather within the nanoparticles at high local catalyst and substrate concentrations. We evaluated six different amphiphilic polymeric nanoparticles to assess the effect of polymer length, catalyst loading and nature of the catalyst (PTH or ACR) in the dechlorination of a range of aromatic chlorides. In addition, we investigate the selectivity of both catalysts for reducing different types of aryl-halogen bonds present in one molecule, as well as the activity of the catalysts for C-C cross-coupling reactions. We find that all polymer-based catalysts show high activity for the reduction of electron-poor aromatic compounds. For electron-rich compounds, the ACR-based catalyst is more effective than PTH. In the selective dehalogenation reactions, the order of bond stability is C-Cl &gt, C-Br &gt, C-I irrespective of the catalyst applied. All in all, both water-compatible systems show good activity in water, with ACR-based catalysts being slightly more efficient for more resilient substrates.

Self-healing materials can prolong the lifetime of structures and products by enabling the repairing of damage. However, detecting the damage and the progress of the healing process remains an important issue. In this study, self-healing, piezoresistive strain sensor fibers (ShSFs) are used for detecting strain deformation and damage in a self-healing elastomeric matrix. The ShSFs were embedded in the self-healing matrix for the development of self-healing sensor fiber composites (ShSFC) with elongation at break values of up to 100%. A quadruple hydrogen-bonded supramolecular elastomer was used as a matrix material. The ShSFCs exhibited a reproducible and monotonic response. The ShSFCs were investigated for use as sensorized electronic skin on 3D-printed soft robotic modules, such as bending actuators. Depending on the bending actuator module, the electronic skin was loaded under either compression (pneumatic-based module) or tension (tendon-based module). In both configurations, the ShSFs could be successfully used as deformation sensors, and in addition, detect the presence of damage based on the sensor signal drift. The sensor under tension showed better recovery of the signal after healing, and smaller signal relaxation. Even with the complete severing of the fiber, the piezoresistive properties returned after the healing, but in that case, thermal heat treatment was required. With their resilient response and self-healing properties, the supramolecular fiber composites can be used for the next generation of soft robotic modules.

We present the results of a three-dimensional kinetic Monte Carlo (3D KMC) simulation study of the current density and efficiency of a prototypical green phosphorescent organic light-emitting diode within which the TPBi [2,${2}^{\ensuremath{'}}$,${2}^{\ensuremath{''}}$-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)] molecules that comprise the electron transport layer have a large (7 D) static dipole moment. By explicitly calculating the dipole-induced electrostatic field distribution the additional energetic disorder and the additional internal electrostatic field due to the small net dipole-moment orientation in TPBi are included in a mechanistic manner. The simulation results are compared with the results of an experimental study by B. Sim et al. [ACS Appl. Mater. Interf. 8, 33010 (2016)]. Using a set of simulation parameters that provides a fair agreement with the experimental voltage-dependent current density, external quantum efficiency, and emission profiles, the simulations are used to study the sensitivity to the size and net orientation of the dipole moments. We show how the dipole-induced disorder and the dipole orientation affect the current density, the electron injection efficiency, the blocking of holes by the TPBi layer, the shape of the emission profile, and the quantum efficiency. A key element of the validation of the simulations is a comparison with measured emission profiles, which Sim et al. obtained from sense layer experiments. Explicit KMC simulations of these experiments are used to investigate the expected accuracy with which the emission profiles are probed.

High molar mass polycarbonate is synthesized via a solution transcarbonation of bis(methyl salicyl) carbonate and bisphenol-A at temperatures between 60 and 160 °C without the removal of the condensate, allowing the incorporation of thermosensitive monomers into polycarbonate. Kinetic and equilibrium studies show that the polymerization is 20–30 times faster at 120 °C compared to 60 °C, whereas the equilibrium Mw increases from 11 × 103 g mol−1 at 120 °C to 16 × 103 g mol−1 at 60 °C. This polycondensation is characterized by very high equilibrium constants ranging from 0.8 × 103 at 160 °C to 4.1 × 103 at 60 °C, corresponding to standard enthalpies and entropies of polymerization: −19 kJ mol−1 < ΔH0 < −11 kJ mol−1 and 13 J mol−1 K−1 < ΔS0 −1 K−1. Without removal of the condensate, the system is shown to be dynamic and completely reversible when changing the temperature. Good predictability of this polycondensation is reported, where only at very low starting monomer concentrations, the formation of cyclics leads to deviations from the predicted behavior.

Achieving long-range order with surface-supported supramolecular assemblies is one of the pressing challenges in the prospering field of non-covalent surface functionalization. Having access to defect-free on-surface molecular assemblies will pave the way for various nanotechnology applications. Here we report the synthesis of two libraries of naphthalenediimides (NDIs) symmetrically functionalized with long aliphatic chains (C28 and C33) and their self-assembly at the 1-phenyloctane/highly oriented pyrolytic graphite (1-PO/HOPG) interface. The two NDI libraries differ by the presence/absence of an internal double bond in each aliphatic chain (unsaturated and saturated compounds, respectively). All molecules assemble into lamellar arrangements, with the NDI cores lying flat and forming 1D rows on the surface, while the carbon chains separate the 1D rows from each other. Importantly, the presence of the unsaturation plays a dominant role in the arrangement of the aliphatic chains, as it exclusively favors interdigitation. The fully saturated tails, instead, self-assemble into a combination of either interdigitated or non-interdigitated diagonal arrangements. This difference in packing is spectacularly amplified at the whole surface level and results in almost defect-free self-assembled monolayers for the unsaturated compounds. In contrast, the monolayers of the saturated counterparts are globally disordered, even though they locally preserve the lamellar arrangements. The experimental observations are supported by computational studies and are rationalized in terms of stronger van der Waals interactions in the case of the unsaturated compounds. Our investigation reveals the paramount role played by internal double bonds on the self-assembly of discrete large molecules at the liquid/solid interface.

Mechanoresponsive polymers with intense red emission are highly desirable in view of the strong penetrability and high resolution of red luminescence. Herein we introduce the sensitized luminescence of rare-earth Eu(III) complexes into the mechanochemiluminescence from polymeric dioxetane in a covalent way. By controlling the energy-Transfer process from mechanically broken dioxetane to the Eu(III) center, bright red emission from transparent poly(methyl acrylate) films was achieved for the first time. Importantly, mechanoluminescence sensitivity is greatly improved, enabling the location and timing of bond scission with high resolution. A sensitive stretchable device with the polymer film as an emissive layer was fabricated by a facile surface-engineering method, which can emit patterned red light upon deformation. This sensitized mechanoluminescence design thus expands the useful space of luminescent stress probes.

The accessibility of renewable materials that are both sustainable and competitive is essential to accommodate the rapid growth in consumption of 3D printing materials. We have developed biobased photopolymer resins based on modified soybean oil for application in commercial stereolithography printers. First, soybean oil methacrylates with various functionalities were successfully synthesized from epoxidized soybean oil as an alternative to commercially available soybean oil acrylate. A library of photoresins was created by mixing up to 80% of the biobased (meth)acrylate oligomers with biobased diluents and a photoinitiator. The resin composition was optimized to achieve a maximum biobased content and a low viscosity. The manufactured parts demonstrated complete layer fusion and accurate print quality. Stiffness and toughness can be tuned by altering the chemical composition or the number of functional groups per oligomer. These biobased materials can be employed to reduce the environmental impact of additive manufacturing while being competitive with current fossil-based resins from commercial manufacturers.

Significant improvement in mechanical properties and shape recovery in polyurethanes can be obtained by cross-linking, usually performed in a traditional chemical fashion. Here, we report model studies of enzymatic transamidations of urethane-bond-containing esters to study the principles of an enzymatic build-up of covalent cross-linked polyurethane networks via amide bond formation. The Lipase-catalyzed transamidation reaction of a urethane-bond-containing model ester ethyl 2-(hexylcarbamoyloxy)propanoate with various amines is discussed. A side product was formed, that could be successfully identified, and its synthesis reduced to a minimum (

Access to versatile and stable nanostructures formed by the self-assembly of block copolymers in water is essential for biomedical applications. These applications require control over the stability, morphology, and size of the formed nanostructures. Here, we study the self-assembly in water of a library of fully discrete and sequence-controlled AB-type block co-oligomers (BCOs) of oligo(l-lactic acid)-b-oligo(ethylene glycol). In this series, we eliminate all the inherent uncertainty associated with molar mass, ratio, and compositional dispersity, but vary the ratio between the water-soluble and water-insoluble parts. The BCO library is designed in such a way that vesicles, spherical micelles, and cylindrical micelles are generated in solution, hereby covering a variety of common morphologies. With the help of self-consistent field (SCF) computations, the thermodynamic structures in water are predicted for all structures. The morphologies formed were experimentally analyzed using a combination of calorimetry and scattering techniques. When comparing the experimentally found structures with those predicted, we find an excellent agreement. Intriguingly, calorimetry showed the presence of crystallized l-lactic acid (LLA) units in the bilayer of the lamellar forming BCO. Despite this crystallinity, there is no mismatch between the predicted and observed bilayer thicknesses upon self-assembly in water. In this case, phase separation driven by the hydrophobic LLA block coincides with crystallization, resulting in stable morphologies. Thus, SCF guided library design and sample preparation can lead toward robust formulations of nanoparticles.

The lipase-catalyzed synthesis of furan-comprising polyester oligomer diols (α,ω-telechelic diols) is reported. Oligofuranoate diols with excellent end-group fidelity and a yield of 95% were synthesized using a solvent-free two-stage polycondensation of dimethyl furan-2,5-dicarboxylate (DMFDCA) and 1,4-cyclohexanedimethanol (1,4-CHDM) using immobilized Candida antarctica Lipase B (CalB). Recycling of immobilized CalB to further decrease the production cost is successfully demonstrated. However, it showed limitation in the product yield that decreases ±20% with each additional reuse. The synthetic procedure has been scaled up, easily opening the possibility to use the developed diols in industrial polycondensations utilizing the excellent flame retardancy property and high thermal stability typical for furan-based polymers.

The development of more sustainable materials with a prolonged useful lifetime is a key requirement for a transition towards a more circular economy. However, polymer materials that are long-lasting and highly durable also tend to have a limited application potential for re-use. This is because such materials derive their durable properties from a high degree of chemical connectivity, resulting in rigid meshes or networks of polymer chains with a high intrinsic resistance to deformation. Once such polymers are fully synthesised, thermal (re)processing becomes hard (or impossible) to achieve without damaging the degree of chemical connectivity, and most recycling options quickly lead to a drop or even loss of material properties. In this context, both academic and industrial researchers have taken a keen interest in materials design that combines high degrees of chemical connectivity with an improved thermal (re)processability, mediated through a dynamic exchange reaction of covalent bonds. In particular vitrimer materials offer a promising concept because they completely maintain their degree of chemical connectivity at all times, yet can show a clear thermally driven plasticity and liquid behavior, enabled through rapid bond rearrangement reactions within the network. In the past decade, many suitable dynamic covalent chemistries were developed to create vitrimer materials, and are now applicable to a wide range of polymer matrices. The material properties of vitrimers, however, do not solely rely on the chemical structure of the polymer matrix, but also on the chemical reactivity of the dynamic bonds. Thus, chemical reactivity considerations become an integral part of material design, which has to take into account for example catalytic and cross-reactivity effects. This mini-review will aim to provide an overview of recent efforts aimed at understanding and controlling dynamic cross-linking reactions within vitrimers, and how directing this chemical reactivity can be used as a handle to steer material properties. Hence, it is shown how a focus on a fundamental chemical understanding can pave the way towards new sustainable materials and applications., In this minireview, we survey recent advances in the development of vitrimer materials. Focus on how to chemically control their material properties is used to highlight challenges for boosting the potential of this emerging class of polymer materials.

Recently, poly(allyl glycidyl ether) (PAGE) has attracted great interest as a polymer electrolyte for Li-ion transport with conductivity values well above that of the benchmark polyethylene oxide polymer at temperatures below 60 °C. Here, we prepared lithium and magnesium polyelectrolytes by using two novel PAGE-based matrixes containing thioether and sulfone functionalities located in a short side chain inserted by the chemical post-functionalization of PAGE. The synthesized PAGEs, poly(2-(ethyl thio) propyl glycidyl ether) (PEthioPGE) and poly(2-(ethyl sulfone) propyl glycidyl ether) (PEsulfoPGE), were all amorphous at any temperature with Tg between-80 °C and-30 °C. These polymers were used to formulate electrolytes with different Li and Mg salts. The impact of the side chain, used salt and temperature on the ionic conductivity was studied in detail. Ionic conductivities as high as 5.1 × 10-4 S cm-1 at 90 °C can be achieved using PAGE-LiTFSI and PEthioPGE-LiTFSI, values comparable to that achieved using PEO-LiTFSI with identical salt loading. When LiCl is used, PEthioPGE outperforms all other polymers including PEO with the highest conductivity value at 90 °C (1.1 × 10-5 S cm-1). Moreover, the studied complexes with magnesium salts showed promising ionic conductivities, comparable to those achieved using lithium and up to 4.1 × 10-4 S cm-1 at 90 °C for PAGE-Mg(TFSI)2. The results presented here highlight the possibility of tuning the structures and the complexation properties of poly(glycidyl ether)-based electrolytes towards both lithium and magnesium ions.

Non-covalently crosslinked polymeric networks are promising materials towards sustainable and recyclable plastics. Here, we present the post-functionalization of poly(dimethyl siloxane) (PDMS) with supramolecular moieties, attached as grafts to the PDMS backbone, to obtain recyclable PDMS networks. We select three different supramolecular motifs that differ in interaction strength and investigate how these differences affect the dynamic behavior of the networks. The introduction of dinitrohydrazones (hydz), which afford weak supramolecular interactions by π-stacking, resulted in a viscous material at room temperature. Stronger self-association was achieved by the introduction of benzene-1,3,5-carboxamides (BTAs) and ureidopyrimidinones (UPys), which self-assemble via triple and quadruple hydrogen bonding, respectively. This resulted in a thermoplastic elastomeric material for BTA-based PDMS and brittle materials for Upy-based PDMS. Time- and temperature-dependent mechanical measurements reveal that the dynamic nature of the supramolecular bonds becomes slower upon increasing the interaction strength. The polymers are fully recyclable by solvation or compression molding without the loss of material properties. Thereby, by using one linear PDMS backbone, we demonstrate how fundamentally different material properties are obtained by changing the supramolecular interaction strength and type of non-covalent crosslinks. These molecular insights broaden the scope and application of PDMS-based sustainable materials.

In this work, we provide a detailed study on the influence of patch size and chemistry on the catalytic activity of patchy hybrid nonwovens in the gold nanoparticle (Au NP) catalysed alcoholysis of dimethylphenylsilane in n-butanol. The nonwovens were produced by coaxial electrospinning, employing a polystyrene solution as the core and a dispersion of spherical or worm-like patchy micelles with functional, amino group-bearing patches (dimethyl and diisopropyl amino groups as anchor groups for Au NP) as the shell. Subsequent loading by dipping into a dispersion of preformed Au NPs yields the patchy hybrid nonwovens. In terms of NP stabilization, i.e., preventing agglomeration, worm-like micelles with poly(N,N-dimethylaminoethyl methacrylamide) (PDMA) patches are most efficient. Kinetic studies employing an extended 1(st) order kinetics model, which includes the observed induction periods, revealed a strong dependence on the accessibility of the Au NPs' surface to the reactants. The accessibility is controlled by the swellability of the functional patches in n-butanol, which depends on both patch chemistry and size. As a result, significantly longer induction (t(ind)) and reaction (t(R)) times were observed for the 1(st) catalysis cycles in comparison to the 10(th) cycles and nonwovens with more polar PDMA patches show a significantly lower t(R) in the 1(st) catalysis cycle. Thus, the unique patchy surface structure allows tailoring the properties of this "tea-bag"-like catalyst system in terms of NP stabilization and catalytic performance, which resulted in a significant reduction of t(R) to about 4 h for an optimized system.

We report on the epitaxial growth of photoresponsive alkyl-substituted azobenzene fibres on top of uniaxially oriented polyethylene (PE) films. In these fibres, the alkyl chains are oriented parallel with regard to the drawing direction of PE, whereas the azobenzene moieties pack into a roughly 60° angle. The bilayer films act as a light responsive actuator generating an actuation stress of about 3 MPa.

Different types of butyl acrylate (BA)-co-acrylic acid (AA) oligomers were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and mixed with extruded 200 nm dimethyldioctadecylammonium bromide vesicles. The resulting precursor structures form the basis for subsequent vesicle-templated polymerizations. Systematic variations in temperature, pH, oligomer length, and oligomer composition and their effects on precursor morphology were studied. Surprisingly, different morphologies were obtained, including capsules, protruded capsules, solid spheres, and multicompartment structures. For example, capsules and multicompartment structures were found to result from higher AA contents, and protruded capsules and solid particles resulted from lower AA contents. Subsequent chain extension of the RAFT oligomers resulted in polymer nanostructures resembling the precursor morphologies.

A range of copolymers of methacrylic acid (MAA) macromonomers prepared by cobalt-catalyzed chain transfer and methyl methacrylate (MMA) and/or butyl acrylate (BA) was synthesized and used as a stabilizer in the emulsion polymerization of MMA. Although clear differences were observed in polymerization rates using the different MAAx-MMAy stabilizers, these differences were not as clearly reflected in the particle sizes nor in the rates per particle. However, a clear difference between these systems and those stabilized by MAAx-BAy was observed. The latter systems were all characterized by much smaller particle sizes and corresponding higher rates of polymerization. In addition, the molar masses in the latter systems were all significantly larger than those obtained in the MAAx-MMAy stabilized system, in which the stabilizers act as "sulfur-free" RAFT agents. Interestingly, the prepared latexes showed a range of appearances varying from "milky" to "gel-like" depending on the used stabilizer. The MAAx-BAy stabilized latexes had, in general, a lower viscosity and a significantly smaller (if any) yield stress than the MAAx-MMAy stabilized latexes, and in the latter case the rheological behavior was found to depend on the block lengths in and concentration of the stabilizer.

Ruddlesden-Popper perovskite films deposited with different methods show very diverse phase segregation and composition. When DMSO is used as solvent, the conventional method based on spin-coating and annealing produces very poor devices, whereas the vacuum-assisted method proposed here allows obtaining devices with efficiency up to 14.14%. The conventional method gives rise to a three-dimensional (3D)-like phase on the top of the film but dominant n = 2 phase with large domains (∼40 μm) at the bottom of the film. These n = 2 domains are oriented with their inorganic slabs parallel to the substrate and inhibit the charge transport in the vertical direction. Consequently, severe monomolecular and bimolecular charge recombination occurs in the solar cells. Conversely, the vacuum-assisted method yields films with a 3D-like phase dominant throughout their entire thickness and only a small amount of n ≤ 2 domains of limited dimensions (∼3 μm) at the bottom, which facilitate charge transport and reduce charge recombination.

Elucidating the microstructure of supramolecular copolymers remains challenging, despite the progress in the field of supramolecular polymers. In this work, we present a detailed approach to investigate supramolecular copolymerizations under thermodynamic control. Our approach provides insight into the interactions of different types of monomers and hereby allows elucidating the microstructure of copolymers. We select two monomers that undergo cooperative supramolecular polymerization by way of threefold intermolecular hydrogen bonding in a helical manner, namely, benzene-1,3,5-tricarboxamide (BTA) and benzene-1,3,5-tris(carbothioamide) (thioBTA). Two enantiomeric forms and an achiral analogue of BTA and thioBTA are synthesized and their homo- and copolymerizations are studied using light scattering techniques, infrared, ultraviolet, and circular dichroism spectroscopy. After quantifying the thermodynamic parameters describing the homopolymerizations, we outline a method to follow the self-assembly of thioBTA derivatives in the copolymerization with BTA, which involves monitoring a characteristic spectroscopic signature as a function of temperature and relative concentration. Using modified types of sergeants-and-soldiers and majority-rules experiments, we obtain insights into the degree of aggregation and the net helicity. In addition, we apply a theoretical model of supramolecular copolymerization to substantiate the experimental results. We find that the model describes the two-component system well and allows deriving the hetero-interaction energies. The interactions between the same kinds of monomers (BTA-BTA and thioBTA-thioBTA) are slightly more favorable than those between different monomers (BTA-thioBTA), corresponding to a nearly random copolymerization. Finally, to study the interactions of the monomers at the molecular level, we perform density functional theory-based computations. The results corroborate that the two-component system exhibits a random distribution of the two monomer units along the copolymer chain.

Understanding the molecular level origin of chiroptical properties in enantiopure π-conjugated polymers is essential for tailoring these materials for application in organic light-emitting diodes and photonic devices. Here we have studied poly(9,9′-dialkylfluorene-alt-2,5-dialkoxyphenyl)s as prototypical copolymers to investigate their structure-chiroptical property relationship. The effect of a systematic variation of the location and configuration (S or R) of chiral and achiral side chains in the repeating units on the liquid crystalline ordering and its relationship to chiroptical properties were investigated. The results clearly indicate that enantiopure side chains on the fluorene units are critical for obtaining the cholesteric liquid crystalline ordering and thereby strong chiroptical properties in both absorption and photoluminescence in annealed thin films. Finally, solution-processed organic light-emitting diodes constructed from a liquid crystalline polymer show strong emission of circularly polarized light, demonstrating the potential application of these systems.

This work exploits the scope of doping engineering as an enabler for better-performing and thermally stable n-type organic thermoelectrics. A fullerene derivative with polar triethylene glycol type side chain (PTEG-1) is doped either by "coprocessing doping" with n-type dopants such as n-DMBI and TBAF or by "sequential doping" through thermal deposition of Cs2CO3. Solid-state diffusion of Cs2CO3 appears to dope PTEG-1 in the strongest manner, leading to the highest electrical conductivity of similar to 17.5 S/cm and power factor of 32 mu W/(m K-2). Moreover, the behavior of differently doped PTEG-1 films under thermal stress is examined by electric and spectroscopic means. Cs2CO3-doped films are most stable, likely due to a coordinating interaction between the polar side chain and Cs+-based species, which immobilizes the dopant. The high power factor and good thermal stability of Cs2CO3-doped PTEG-1 make it very promising for tangible thermoelectric applications.

Block copolymers offer the fabrication of mesoporous thin films with distinct nanoscale structural features. In this contribution, we present the use of acetic acid (CH3COOH) as a low‐molecular‐weight guest molecule to tune the supramolecular assembly of poly[styrene‐block‐(4‐vinylpyridine)] (PS‐b‐P4VP), offering a versatile and straightforward method to obtain tailored nanostructured films with controlled topography and pore size. Spin‐coating toluene solutions of PS‐b‐P4VP, with a variable amount of CH3COOH, leads to micellar thin films, where the micelles contain the carboxylic acid as a guest molecule. The size can be conveniently modified in these films (from 48 to 75 nm) by varying the amount of organic acid in the starting solutions. Subsequent surface reconstruction of micellar films using ethanol leads to ring‐shaped copolymer nanoporous films with modulated diameter. Controlling the micelle reconstruction process, cylindrical porous films are also obtained. Interestingly, changing the type of aliphatic carboxylic acid leads to a modification of the observed film morphology from micelles to out‐of‐plane P4VP cylinders (or lamellae) in a PS matrix., This work was supported by Spanish MINECO (grants FIS2013‐45469 and FIS2016‐76058 (AEI/FEDER, EU)).

International audience; Polypeptide nanoparticles were obtained by the miniemulsion polymerization of S-(o-nitrobenzyl)-l-cysteine (NBC) N-carboxyanhydride (NCA). Through process optimization, reaction conditions were identified that allowed the polymerization of the water sensitive NCA to yield nanoparticles of about 220 nm size. Subsequent UV-irradiation of the nanoparticle emulsions caused the in situ removal of the nitrobenzyl group and particle cross-linking through disulfide bond formation accompanied by the shrinkage of the particles.

Contains fulltext : 215330.pdf (Publisher’s version ) (Closed access) To maintain functionality during in situ vascular regeneration, the rate of implant degradation should be closely balanced by neo-tissue formation. It is unknown, however, how the implant's functionality is affected by the degradation of the polymers it is composed of. We therefore examined the macro- and microscopic features as well as the mechanical performance of vascular scaffolds upon in vitro enzymatic degradation. Three candidate biomaterials with supramolecularly interacting bis-urea (BU) hard blocks ('slow-degrading' polycarbonate-BU (PC-BU), 'intermediate-degrading' polycarbonate-ester-BU (PC(e)-BU), and 'fast-degrading' polycaprolactone-ester-BU (PCL-BU)) were synthesized and electrospun into microporous scaffolds. These materials possess a sequence-controlled macromolecular structure, so their susceptibility to degradation is tunable by controlling the nature of the polymer backbone. The scaffolds were incubated in lipase and monitored for changes in physical, chemical, and mechanical properties. Remarkably, comparing PC-BU to PC(e)-BU, we observed that small changes in macromolecular structure led to significant differences in degradation kinetics. All three scaffold types degraded via surface erosion, which was accompanied by fiber swelling for PC-BU scaffolds, and some bulk degradation and a collapsing network for PCL-BU scaffolds. For the PC-BU and PC(e)-BU scaffolds this resulted in retention of mechanical properties, whereas for the PCL-BU scaffolds this resulted in stiffening. Our in vitro study demonstrates that vascular scaffolds, electrospun from sequence-controlled supramolecular materials with varying ester contents, not only display different susceptibilities to degradation, but also degrade via different mechanisms. STATEMENT OF SIGNIFICANCE: One of the key elements to successfully engineer vascular tissues in situ, is to balance the rate of implant degradation and neo-tissue formation. Due to their tunable properties, supramolecular polymers can be customized into attractive biomaterials for vascular tissue engineering. Here, we have exploited this tunability and prepared a set of polymers with different susceptibility to degradation. The polymers, which were electrospun into microporous scaffolds, displayed not only different susceptibilities to degradation, but also obeyed different degradation mechanisms. This study illustrates how the class of supramolecular polymers continues to represent a promising group of materials for tissue engineering approaches.

Due to the inherent flammability of polypropylene (PP), it is limited in the application of flame retardant materials. In this work, a novel char forming agent, hyperbranched phosphorus-containing polyurethane (HPPU), was synthesized and used as efficient char forming agent. When ammonium polyphosphate (APP) was combined with HPPU, APP/HPPU endow PP significantly improved flame retardancy than single APP. Although the total carbon monoxide production (TCOP) of some PP/APP/HPPU composites is higher than that of PP/APP composite, it is still lower than that of neat PP. LOI (limited oxygen index) and UL-94 tests reveal that PP composites with 25 wt% HPPU/APP with ratio of 4:1 are able to reach 27 vol% and V-0 rating, respectively. The addition of 25 wt% APP/HPPU with ratio of 2:1 into PP can result in decrease in peak heat release rate of about 72%, decrease in total heat release of about 38% and decrease in TCOP of about 93%. APP/HPPU promotes PP to form more stable, compact, and continuous char layer which effectively hinder heat and oxygen transfer and protect the inner matrix from decomposition. Thermogravimetric-infrared results reveal that the gas phase flame retardant mechanism of APP/HPPU is the dilution effect of ammonia from APP and the flame inhibition effect of phosphorus-containing species from HPPU.

International audience; Asymmetric poly(1,1-dimethyl silacyclobutane)-block-polystyrene-block-poly(2-vinyl pyridine) (PDMSB-b-PS-b-P2VP) thick films, consisting of a spongelike substructure topped by a nanostructured dense top layer, were produced by combining a fast self-assembly of the triblock terpolymer chains with nonsolvent-induced phase separation (referred as SNIPS). A controlled evolution of the thickness and morphology of the nanostructured top layer was achieved upon solvent vapor annealing (SVA). For instance, the sub-100 nm thick square array morphology generated by SNIPS is transformed into a 1.5 mu m thick core-shell perforated lamellar (PL) structure when exposed to a chloroform (CHCl3) vapor for 3 h. A PL phase having highly ordered continuous P2VP nanochannels can be envisioned as an appealing morphology for membrane applications, since such a network structure formed on asymmetric PDMSB-b-PS-b-P2VP thick films obviates the need for alignment. Monoliths entirely composed of the bicontinuous PL structure were also produced by increasing the duration of the SVA treatment (18 h, CHCl3)

Next-generation organic photovoltaic technology is currently geared towards non-fullerene organic solar cells. Among the non-fullerene small molecule acceptors, ITIC derivatives play a central role with power conversion efficiency above 15% in single junction cells. However, knowledge about the stability of these new types of devices is lagging behind, creating an efficiency-lifetime gap for commercial viability. Here, we study the photostability of three ITIC derivatives, namely ITIC together with IT-M and IT-F, representative of methylated and halogenated ITIC, the usual modification to this small molecule acceptor. While the best performing solar cell yields a PCE of 8.6%, we find that the photostability of the devices greatly depends on the structure of the acceptor and the configuration of the devices. The methylation of ITIC into IT-M improves Voc but does not greatly affect the photostability of the devices. While fluorination generally decreases the efficiency of the cells, the stability of the fluorinated ITIC-based cells appears to depend on the device structure. Thus, the change from ITIC to IT-F may not in all cases necessarily be beneficial to the advancement of the technology. Subtle changes in molecular structure coupled with imbalance charge mobilities is at the origin of the observed differences in degradation.

Polymorphism of organic semiconducting materials exerts critical effects on their physical properties such as optical absorption, emission and electrical conductivity, and provides an excellent platform for investigating structure–property relations. It is, however, challenging to efficiently tune the polymorphism of conjugated polymers in aggregated, semi-crystalline phases due to their conformational freedom and anisotropic nature. Here, two distinctly different semi-crystalline polymorphs (β1 and β2) of a low-bandgap diketopyrrolopyrrole polymer are formed through controlling the solvent quality, as evidenced by spectroscopic, structural, thermal and charge transport studies. Compared to β1, the β2 polymorph exhibits a lower optical band gap, an enhanced photoluminescence, a reduced π-stacking distance, a higher hole mobility in field-effect transistors and improved photocurrent generation in polymer solar cells. The β1 and β2 polymorphs provide insights into the control of polymer self-organization for plastic electronics and hold potential for developing programmable ink formulations for next-generation electronic devices., Tuning polymorphism of conjugated polymers, though a promising method for studying and controlling the structure-property relations in these materials remains a challenge. Here, the authors identify two aggregated semi-crystalline polymorphs of a low-bandgap diketopyrrolopyrrole-based polymer.

Polymer solar cells are potentially key contributors to the next-generation organic photovoltaics for sustainable green sources of energy. In the past few years, ternary organic solar cells have emerged with promising characteristics. They have proven to yield high efficiency at about 15% for single junction donor:acceptor (D:A) solar cells. However, the low stability of organic solar cells is a hindrance to the commercialisation of this technology, and thus, needs more attention. Here, we show that with the right ratio of D : A1 : A2, ternary blend solar cells can be more efficient and more photostable than their D:A binary blend solar cells. We add [70]PCBM to PBDB-T:ITIC and PTB7-Th:ITIC binary blend solar cells in various ratios to fabricate ternary solar cells. The ternary solar cells outperform all binary cells in terms of efficiency and photostability with only a 10% average loss in efficiency under continuous illumination irrespective of the device structure. We identify changes in the molecular structure of the active layer blends as the main reason behind the observed degradation behaviour of the solar cells. The ternary blends are the most resilient to photo-induced molecular structural changes. This finding suggests that ternary organic solar cells could be a way to achieve photostable devices.