Aqueous dispersions of organic semiconducting nanoparticles (NPs) are particularly attractive as inks for the environmentally friendly preparation of organic solar cells. The internal morphology of the NPs, which depends on their elaboration process, is a key parameter, which has a significant influence on the final morphology of the active layer and therefore its effectiveness. In the present study, core-shell (PF2:PC71BM) NPs were prepared by miniemulsion. Their internal morphology including the composition of the two phases was characterized by scanning transmission X-ray microscopy (STXM) showing a core composed of 77% PC71BM and a shell composed of 75% PF2. It was found that thermal annealing promotes PC71BM diffusion from the core to the shell, increasing its proportion in the shell from 25% to 42%. This annealing, when applied after NPs deposition by spincoating, allows partial coalescence of the NPs, reducing the roughness of the active layer, and increases electron mobility, thus demonstrating the formation of PC71BM percolation paths for electron transport. A PCE of 1.6% could thus be obtained after 10 min of thermal annealing at 100◦C. At higher temperature, Grazing- Incidence Wide-Angle X-Ray Scattering (GIWAXS) analyses demonstrate the modification of the PF2 structura- tion from randomly oriented lamella after deposition to edge-on orientation after annealing, leading to an un- favorable decrease of the hole mobility in the direction perpendicular to the substrate, while increasing the hole mobility in the substrate plane. This study demonstrates the need to systematically characterize the internal morphology of NPs in order to rationalize the morphology of the active layer and optimize its properties.

https://doi.org/10.1016/j.synthmet.2024.117599

Supramolecular electronics exploits the distinctive features stemming from noncovalent interactions, guiding the self-assembly of molecules to craft materials endowed with customized electronic functionalities. Hydrogen-bonded materials, characterized by their capacity to establish dynamic and stable networks, introduce an extra dimension to the development of supramolecular electronic systems. This study presents a comparative analysis of two remarkably small semiconductors utilizing diketopyrrolopyrrole functionalized with urea units as hydrogen-bonding motifs, strategically positioned at opposing ends of the conjugated core. We show how the subtle distinction in functionalization not only influences morphology and self-assembly dynamics via hydrogen-bonding and π-π stacking formation, but also holds significant consequences for ultimate charge transport properties. Our observations into the interplay of noncovalent interactions provide valuable insights and strategic pathways for the design of novel materials with enhanced electronic characteristics.

https://doi.org/10.1002/chem.202400392

Swapneel Vijay Thakkar ^a, Turkan Nabiyeva ^a, Quentin Weinbach ^a, Harsh Bhatia ^b, Zilu Liu ^b, Tom Ferté ^c, Cédric Leuvrey ^c, Alain Carvalho ^a, Bob C. Schroeder ^b, Laure Biniek ^a

Polymer 296 ( 2024) 126761

Sruthi Suresh, Turkan Nabiyeva, Laure Biniek,* and E. Bhoje Gowd*

ACS Polym. Au, 2024 

Strategic customization of crystalline forms of poly(vinylidene fluoride) (PVDF) aerogels is of great importance for a variety of applications, from energy harvesters to thermal and acoustic insulation. Here, we report sustainable strategies to prepare crystalline pure α, β, and γ forms of PVDF aerogels from their respective gels using a solvent exchange strategy with green solvents, followed by a freeze-drying technique. The crucial aspect of this process was the meticulous choice of appropriate solvents to enable the formation of thermoreversible gels of PVDF by crystallization-induced gelation. Depending on the polymer−solvent interactions, the chain conformation of PVDF can be modulated to obtain gels and aerogels with specific crystalline structures. The crystalline pure α-form and piezoelectric β-form aerogels were readily obtained by using cyclohexanone and γ-butyrolactone as gelation solvents. On the other hand, the γ-form aerogel was obtained using a binary solvent system consisting of dimethylacetamide and water. These aerogels with distinct crystalline structures exhibit different morphologies, mechanical properties, hydrophobicities, acoustic properties, and electrical properties. Measurement of thermal conductivity for these aerogels showed exceptionally low thermal conductivity values of ∼0.040 ± 0.003 W m−1 K−1 irrespective of their crystal structures. Our results showcase the fabrication approaches that enable PVDF aerogels with varied physicochemical properties for multifunctional applications.

Lambert Sicard,  Clément Brouillac,  Nicolas Leclerc, Sadiara Fall, Nicolas Zimmerman, Olivier Jeannin, Joëlle Rault-Berthelot, Cassandre Quinton  and  Cyril Poriel.

Materials Chemistry Frontiers, 2024  DOI: 10.1039/d3qm01106b

1-Substituted fluorenes have emerged in recent years as being among the most efficient functional materials for phosphorescence and thermally activated delayed fluorescence OLEDs. The position C1 of the fluorene is indeed highly interesting to design functional materials with specific properties. This scaffold displays two main characteristics. First, there is a strong p-conjugation disruption between the pendant substituent attached at C1 and the substituted fluorene. Second, the specific geometry of the C1-fluorene allows through-space interactions between the substituent attached at C1 and the cofacial building unit attached at C9. However, to date, this family of organic-semi-conductors has not been intensively studied yet. In this work, we report the synthesis and the structural, electrochemical and photophysical properties of four 1-substituted spirobifluorene derivatives, constructed with widely known extended p-conjugated systems: naphthalene, anthracene, phenanthrene and pyrene at the C1 position of spirobifluorene. Using a structure–property relationship approach, we show how the nature of the substituent grafted at C1 significantly modifies the electronic properties (HOMO/LUMO energy levels, triplet state energy levels, etc.). As 1-substituted spirobifluorenes are undoubtedly very promising organic semi-conductors, such a study provides fundamental knowledge to construct future efficient organic materials for specific applications.

Aditya Dash, Shubhradip Guchait, Dorothea Scheunemann, Vishnu Vijayakumar, Nicolas Leclerc, Martin Brinkmann, and Martijn Kemerink

Adv. Mater. 2023, 2311303 [DOI: 10.1002/adma.202311303]

The possibility to control the charge carrier density through doping is one of the defining properties of semiconductors. For organic semiconductors, the doping process is known to come with several problems associated with the dopant compromising the charge carrier mobility by deteriorating the host morphology and/or introducing Coulomb traps. While for inorganic semiconductors these factors can be mitigated through (top-down) modulation doping, this concept has not been employed in organics. Here, this work shows that properly chosen host/dopant combinations can give rise to spontaneous, bottom-up modulation doping, in which the dopants preferentially sit in an amorphous phase, while the actual charge transport occurs predominantly in a crystalline phase with an unaltered microstructure, spatially separating dopants and mobile charges. Combining experiments and numerical simulations, this work shows that this leads to exceptionally high conductivities at relatively low dopant concentrations.