Guillaume Fleury

Block Copolymer as a Nanostructuring Agent for High‐Efficiency and Annealing‐Free Bulk Heterojunction Organic Solar Cells

The addition of a block copolymer to the polymer/fullerene blend is a novel approach to the fabrication of organic solar cells. The block copolymer (P3HT-b-P4VP) is used as nanostructuring agent in the active layer. A significant enhancement of the cell efficiency is observed, in correlation with morphology control, both before (as-cast) and after the annealing process.

Optimization of the Bulk Heterojunction Composition for Enhanced Photovoltaic Properties: Correlation between the Molecular Weight of the Semiconducting Polymer and Device Performance

Herein we propose an approach toward the optimization of the photovoltaic performance of bulk heterojunctions by tuning the composition of the active layer with respect to the molecular weight of the semiconducting polymer. We used a poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blend as a typical system and varied the molecular weight of the P3HT semiconducting polymer in order to determine its influence on the bulk heterojunction morphology as well as on the optoelectronic characteristics of the device. We have systematically mapped out the phase diagram for different molecular weight P3HTs blended with PCBM and observed the presence of a eutectic composition, which shifts to higher content of P3HT for lower molecular weight P3HTs. This shift inherent to the P3HT molecular weight is also apparent in the photovoltaic performance as the eutectic composition corresponds to the best of the photovoltaic properties. The P3HT molecular weight dependence of the eutectic composition is due to the molecular weight dependence of the P3HT crystallization behavior, which leads to dramatic morphological changes of the bulk heterojunction.

Precision Synthesis of Poly(Ionic Liquid)‐Based Block Copolymers by Cobalt‐Mediated Radical Polymerization and Preliminary Study of Their Self‐Assembling Properties

A poly(ionic liquid)-based block copolymer (PIL BCP), namely, poly(vinyl acetate)-b-poly(N-vinyl-3-butylimidazolium bromide), PVAc-b-PVBuImBr, is synthesized by sequential cobalt-mediated radical polymerization (CMRP). A PVAc precursor is first prepared at 30 °C in bulk by CMRP of VAc, using bis(acetylacetonato)cobalt(II), Co(acac)2, and a radical source (V-70). Growth of PVBuImBr from PVAc-Co(acac)2 is accomplished by CMRP in DMF/MeOH (2:1, v/v). This PIL BCP self-assembles in the sub-micron size range into aggregated core-shell micelles in THF, whereas polymeric vesicles are observed in water, as evidenced by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Thin-solid sample cut from raw materials analyzed by TEM shows an ordered lamellar organization by temperature-dependent synchrotron small-angle X-ray scattering (SAXS). Anion exchange can be accomplished to achieve the corresponding PIL BCP with bis(trifluorosulfonyl)imide (Tf2 N(-)) anions, which also gives rise to an ordered lamellar phase in bulk samples. A complete suppression of SAXS second-order reflection suggests that this compound has a symmetric volume fraction (f ≈ 0.5). SAXS characterization of both di- and triblock PIL BCP analogues previously reported also shows a lamellar phase of very similar behavior, with only an increase of the period by about 8% at 60 °C.

Nanoscale Block Copolymer Ordering Induced by Visible Interferometric Micropatterning: A Route towards Large Scale Block Copolymer 2D Crystals

We have overcome the cost and time consumption limitations of common lithography techniques used to control the self-assembly of block copolymers into highly ordered 2D arrays through the use of a guiding pattern created from a polymeric sub-layer. The guiding pattern is a sinusoidal surface-relief grating interferometrically inscribed onto an azobenzene containing copolymer sub-layer leading to a defect-free single grain of block copolymer domains.

Sub‐10 nm Features Obtained from Directed Self‐Assembly of Semicrystalline Polycarbosilane‐Based Block Copolymer Thin Films

Highly-ordered arrays with sub-10 nm features are produced with topographical-directed self-assembly of low-molecular-weight poly(1,1-dimethyl silacyclobutane)-block-poly(methyl methacrylate). This system turns out to be of high interest for lithographic applications since the domain orientation is solely controlled through the polymer layer thickness, while the promotion of the microphase separation is obtained by a short thermal annealing process under mild conditions.

Optimization of block copolymer self-assembly through graphoepitaxy: A defectivity study

In this paper we report a synoptic methodology to evaluate and optimize the long-range order induced by graphoepitaxy of block copolymer (BCP) self-assembly. The authors focus the study on a BCP that produces hexagonally packed arrays of cylinders oriented perpendicular to the substrate with the copolymer film thickness greater than the trench depth. Prepatterned structures used in the graphoepitaxy approach have been generated by e-beam lithography on a commercial hydrogen silesquioxane resist. A suitable surface modification was accomplished by grafting a random polystyrene-r-poly(methyl methacrylate) copolymer on the prepatterned surfaces. The polystyrene-b-poly(methyl methacrylate) was spin-coated and annealed in order to generate the desired self-assembly. Since the self-assembly process is based on a thermodynamic mechanism, the induced defectivity needs to be reassessed with respect to the standard lithographic process. Using the cylinder center coordinates, a Delaunay triangulation is performed to find the nearest neighbors. This triangulation enables us to easily locate the disclinations which are characterized by having a number of nearest neighbors different from six. Thus, the number of defects can be quantified precisely. Additionally, this methodology affords an accurate evaluation of both the optimum mesa and trench critical dimensions yielding defect-free surfaces and may be extended to monitor the robustness of the BCP directed self-assembly process. Such diagnostics are critical in the implementation of large scale industrial processes.

Scaling-down lithographic dimensions with block-copolymer materials: 10-nm-sized features with poly(styrene)-block-poly(methylmethacrylate)

Abstract. Poly(styrene)-block-poly(methylmethacrylate) (PS-b-PMMA) block-copolymers (BCP) systems synthesized on an industrial scale and satisfying microelectronic’s requirements for metallic contents specifications are studied in terms of integration capabilities for lithographic applications. We demonstrate in particular that this kind of polymer can efficiently achieve periodic features close to 10 nm. These thin films can be transferred in various substrates through dry-etching techniques. The self-assembly optimization for each polymer is first performed on freesurface, leading to interesting properties, and the changes in self-assembly rules for low molecular-weight polymers are investigated and highlighted through different graphoepitaxy approaches. The improvements in self-assembly capabilities toward low periodic polymers, as well as the broad range of achievable feature sizes, make the PS-b-PMMA system very attractive for lithographic CMOS applications. We conclude by showing that high-χ polymer materials developed in Arkema’s laboratories can be efficiently used to reduce the pattern’s size beyond the ones of PS-b-PMMA based BCP’s capabilities.

Structurally-driven Enhancement of Thermoelectric Properties within Poly(3,4-ethylenedioxythiophene) thin Films

Due to the rising need for clean energy, thermoelectricity has raised as a potential alternative to reduce dependence on fossil fuels. Specifically, thermoelectric devices based on polymers could offer an efficient path for near-room temperature energy harvesters. Thus, control over thermoelectric properties of conducting polymers is crucial and, herein, the structural, electrical and thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films doped with p-toluenesulfonate (Tos) molecules were investigated with regards to thin film processing. PEDOT:Tos thin films were prepared by in-situ polymerization of (3,4-ethylenedioxythiophene) monomers in presence of iron(III) p-toluenesulfonate with different co-solvents in order to tune the film structure. While the Seebeck coefficient remained constant, a large improvement in the electrical conductivity was observed for thin films processed with high boiling point additives. The increase of electrical conductivity was found to be solely in-plane mobility-driven. Probing the thin film structure by Grazing Incidence Wide Angle X-ray Scattering has shown that this behavior is dictated by the structural properties of the PEDOT:Tos films; specifically by the thin film crystallinity combined to the preferential edge-on orientation of the PEDOT crystallites. Consequentially enhancement of the power factor from 25 to 78.5 μW/mK2 has been readily obtained for PEDOT:Tos thin films following this methodology.

Pattern density multiplication by direct self assembly of block copolymers: toward 300mm CMOS requirements

In this paper we investigate the possibility to reach 300mm CMOS requirements by integrating graphoepitaxy of PS-b-PMMA self-assembly. Different schemes to integrate DSA process by using 193nm dry lithography or e-Beam lithography will be presented. Moreover, several challenges like solvent compatibility, bake kinetics and defectivity will be addressed. Concerning defectivity, we will propose a methodology in order to evaluate and optimize the long range order induced by graphoepitaxy of the block copolymer DSA. This approach affords the monitoring of the overall block copolymer self-assembly process and enables us to easily optimize the parameters required for a long-range order structuration, leading to a near zero-defects block copolymers self-assembled arrays. Transfer capabilities of the PS masks in the bulk silicon substrate by using plasma-etching will be also detailed, both with the film on bare silicon or organized with graphoepitaxy approaches. These results show the high potential of DSA to be integrated directly into the conventional CMOS lithography process in order to achieve high resolution and pattern density multiplication, at a low cost.

Hexagonal-to-cubic phase transformation in composite thin films induced by FePt nanoparticles located at PS/PEO interfaces.

The organization process of asymmetric poly(styrene-block-ethylene oxide) (PS-b-PEO) copolymer thin films blended with FePt nanoparticles is studied. In a first step, it is shown that FePt nanoparticles stabilized by oleic acid ligands are distributed within the PS matrix phase, whereas the same particles partially covered with short dopamine-terminated-methoxy poly(ethylene oxide) (mPEO-Dopa) are located at PS/PEO interfaces. The swelling of PS domains, induced by FePt_oleic acid nanoparticles during the solvent annealing process, results in formation of a disordered microstructure in comparison to the well-organized hexagonally close-packed (HCP) cylinder phase formed in the neat PS-b-PEO copolymer. The evolution of the microstructure of PS-b-PEO/FePt_mPEO-Dopa composite has been investigated for different solvent annealing treatments. Under high-humidity conditions during the vapor annealing process, the addition of FePt nanoparticles results in formation of spheres in the film split into terraces. The upper and lower terraces are occupied by spheres organized in an unusual square and HCP phases, respectively. Under low-humidity conditions, undulated PEO cylinders oriented parallel to substrate are formed in the presence of FePt nanoparticles. In this case, we observe that most of the nanoparticles accumulate within the core of topological defects, which induces a low nanoparticle concentration at the PS/PEO interfaces and so stabilizes an intermediate undulated cylinder phase.