Ali Nourdine

This work aims at developing polymer surfaces with enhanced hydrophobicity by controlling both the surface chemistry and the surface structure. As a first step, a chemical surface modification is achieved by the incorporation of a synthetized tailored fluorinated copolymer, named POISE-a (Polymer prOcessing Interface StabilizEr), in a commercial polystyrene matrix. Then, a complementary physical approach based on micro-structuration of a polymer surface is used. Polystyrene films containing various contents of POISE-a were elaborated by a solvent casting method. The structuration of the films was conducted by replicating a texture from a nickel insert using a hot-embossing technique with optimized processing conditions. The beneficial effect of POISE-a on both the wettability properties and the replication efficiency was evaluated by the water/polymer static contact angle and the quantification of the replication rate, respectively. The use of this tailored additive, even at low percentages (i.e., 1 wt.%), associated with the structuration of the PS surface, improves both the hydrophobicity of polystyrene and the robustness of the replication process.

The performance and stability in atmospheric conditions of organic photovoltaic devices can be improved by the integration of stable and efficient photoactive materials as substituent of the chemically unstable poly (3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS), generally used as organic hole transport layer. Promising candidates are p-type transparent conductive oxides, which combine good optoelectronic and a higher mechanical and chemical stability than the organic counterpart. In this work, we synthesize Cu-rich CuCrO₂ thin films by aerosol-assisted chemical vapour deposition as an efficient alternative to PEDOT:PSS. The effect of stoichiometry on the structural, electrical, and optical properties was analysed to find a good compromise between transparency, resistivity, and energy bands alignment, to maximize the photovoltaic performances., Average transmittance and bandgap are reduced when increasing the Cu content in these out of stoichiometry CuCrO₂ films. The lowest electrical resistivity is found for samples synthesized from a solution composition in the 60–70% range. The optimal starting solution composition was found at 65% of Cu cationic ratio corresponding to a singular point in Hackee’s figure of merit of 1 × 10⁻⁷ Ω⁻¹. PBDD4T-2F:PC₇₀BM organic solar cells were fabricated by integrating CuCrO₂ films grown from a solution composition ranging between 40% to 100% of Cu as hole transport layers. The solar cells integrating a film grown with a Cu solution composition of 65% achieved a power conversion efficiency as high as 3.1%, representing the best trade-off of the optoelectronic properties among the studied candidates. Additionally, despite the efficiencies achieved from CuCrO₂-based organic solar cells are still inferior to the PEDOT:PSS counterpart, we demonstrated a significant enhancement of the lifetime in atmospheric conditions of optimal oxides-based organic photovoltaic devices.

We describe the degradation mechanism in a metallic nanowire network subjected to electrical stress. The nanowire network degradation is ascribed, at a very local scale, to hot-spot formation and the subsequent propagation of a spatially correlated disruptive crack.

Mechanical properties of heterogeneous systems based on carbon black (CB) filled semi‐crystalline ethylene butyl acrylate (EBA) copolymer nanocomposites are characterized using nano‐indentation technique. The size effect and CB content dependence on the deformation behavior at room temperature were investigated. The phenomenology for hardness response (H) indicates a typical enhancement of the H when the indentation depth (h) decreases as for the usual elastomeric materials. All H–h curves, fitted according to the Meyer's empirical power law and Franck elasticity model, highlight the so‐called length‐scale‐dependent deformation. Similar trend is observed for the elastic modulus. Furthermore, it is evidenced that the increases of CB content increases the mechanical properties of composites, that is, hardness and elastic modulus. This behavior can be mainly related, on the one hand, to the change of the meso‐structure, formed by the interconnected network of polymer and the aggregates of CB particles and to the nature of the polymer matrix, on the other hand. The mechanical properties characterized from micro and submicron indentations were compared to that characterized at macroscopic scale to highlight the possible correlations between the two scales. This investigation can interest many applications of polymer composites for rubber technology such as tires industry, soft robotic, and adhesives. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47897.

For the first time, an extrusion process is used to produce a perfectly nanostructured organic photoactive layer. Extrusion is an interesting, inexpensive and environment-friendly (solventless) option allowing an industrial production scale for polymer solar cell technology. In this paper, this plausible alternative to the usual large scale wet-processing techniques (inkjet printing, roll-to-roll coating…) was considered in order to elaborate bulk lamellar ordered heterojunctions employing polythiophene and fullerene based materials, as the electron donor and acceptor respectively, which were specifically elaborated for this work. An alternating donor/acceptor (D/A) lamellar structure close to the ideal interpenetrating system was targeted and successfully realized. Continuous D and A domains of about 24 nm were obtained, i.e. size close to the exciton diffusion length (20 nm) for π-conjugated organic materials; a photovoltaic response was evidenced under AM1.5 light simulator conditions. This photovoltaic effect, observed in spite of the presence of insulating polymers (∼61 wt%) added in both semi-conductor materials in order to adjust their viscosities, proves the possible achievement of such a perfect working nano-architectured structure via the extrusion process. The next step, consisting in the use of pure D and A extrudable polymers, should thus lead to high and durable photovoltaic performances. Therefore, this paper opens the way to a new promising OPV processing method: extrusion.