Laurence Vignau

Synthesis and properties of a blue bipolar indenofluorene emitter based on a D-π-A design.

Through a rational design, a novel Donor-Acceptor π-conjugated (D-π-A) blue fluorescent indenofluorene dye, DA-DSF-IF, has been synthesized for application in single-layer Small Molecule Organic Light Emitting Diodes (SMOLEDs). This new blue emitter possesses bipolar properties as well as good morphological and emission color stabilities and has been successfully used in a blue emitting single-layer SMOLED, with performances impressively magnified compared to a nonbipolar indenofluorene emitter.

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.

DiSpiroXanthene-IndenoFluorene: a new blue emitter for nondoped organic light emitting diode applications.

Through an expedient synthesis, a novel blue emitter, DiSpiroXanthene-IndenoFluorene (DSX-IF) has been designed and synthesized. DSX-IF possesses good morphological and color stability upon heating, has a high quantum yield, and may be easily polymerized through anodic oxidation. Small molecule organic light emitting diodes (SMOLEDs), using this promising new dixanthene derivative as a blue emissive layer, exhibit a maximum luminance of ca. 3800 Cd.m(-2) with a luminous efficiency of 1 Cd.A(-1).

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.

Fullerene-capped copolymers for bulk heterojunctions: device stability and efficiency improvements

A fullerene end-capped polymer-compatibilizer based on poly(3-hexylthiophene) (P3HT) was synthesized and demonstrated to have a remarkable effect on both the stability and efficiency of devices made from exemplar P3HT and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). P3HT with ethynyl chain-ends and α-azido-ω-bromo-PS were prepared via Grignard metathesis (GRIM) and atom transfer radical polymerisation, respectively. “Click” chemistry resulted in the preparation of poly(3-hexylthiophene)-block-ω-bromo-polystyrene (P3HT-b-PS-Br), and subsequent atom transfer radical addition chemistry with fullerene (C60) yielded the donor–acceptor block copolymer P3HT-b-PS-C60. Both P3HT-b-PS-Br and P3HT-b-PS-C60 were considered as compatibilizers with P3HT/PCBM blends, with the study detailing effects on active-layer morphology, device efficiency and stability. When used at low concentrations, both P3HT-b-PS-Br (1%) and P3HT-b-PS-C60 (0.5%) resulted in considerable 28% and 35% increases in efficiencies with respect to devices made from P3HT/PCBM alone. Furthermore, P3HT-b-PS-C60 (0.5%) resulted in an important improvement in device stability.

Triphenylamine/tetrazine based π-conjugated systems as molecular donors for organic solar cells

Conjugated systems built by connecting one electron-donor triphenylamine to an electron-withdrawing tetrazine have been prepared using various linkers. We describe here the synthesis, the electrochemical properties and some photophysical properties of these molecules, emphasizing the dependence upon the type of linker between the groups and an organic photovoltaic solar cell was prepared with one derivative.

Synthesis of squaraine-based alternated π-conjugated copolymers: from conventional cross-coupling reactions to metal-free polycondensation

Low band-gap π-conjugated copolymers based on squaraine units alternated with thiophene or benzothiadiazole moieties were synthesized through Suzuki and Stille cross-coupling reactions, and through a metal-free polycondensation process using squaric acid. The metal-free polymerizations afforded higher molecular weights polymers, showing bright future for the synthesis of small band-gap π-conjugated polymers via less cost-effective and more environmental-friendly procedures. Additionally, the synthesized materials showed encouraging optoelectronic properties.

Application of non-metal doped titania for inverted polymer solar cells

Inverted bulk-heterojunction polymer solar cells have been fabricated applying non-metal doped TiO2 as electron extraction buffer layers. Spin-coated films from nitrogen, sulphur, and iodine doped TiO2 nanoparticles dispersed in dimethyl sulphoxide showed comparable roughness and uniformity as those from the pure TiO2 nanoparticles. The highest power conversion efficiency (PCE) of 1.67% was obtained for N-doped TiO2, whereas in the case of pure TiO2, PCE was around 1%. The highest short circuit current density (Jsc = 10.66 mA cm−2) was achieved for I-doped TiO2. Moreover, it was observed that devices with doped TiO2 exhibit better stability under constant illumination comparing to the control devices with pure TiO2.

Material challenges for solar cells in the twenty-first century: directions in emerging technologies

Abstract Photovoltaic generation has stepped up within the last decade from outsider status to one of the important contributors of the ongoing energy transition, with about 1.7% of world electricity provided by solar cells. Progress in materials and production processes has played an important part in this development. Yet, there are many challenges before photovoltaics could provide clean, abundant, and cheap energy. Here, we review this research direction, with a focus on the results obtained within a Japan–French cooperation program, NextPV, working on promising solar cell technologies. The cooperation was focused on efficient photovoltaic devices, such as multijunction, ultrathin, intermediate band, and hot-carrier solar cells, and on printable solar cell materials such as colloidal quantum dots.

Main-chain poly(fullerene) multiblock copolymers as organic photovoltaic donor–acceptors and stabilizers

A multi-block copolymer based on main-chain fullerene repeating units is used in organic photovoltaic devices for the first time. A poly(fullerene) (PFDP) is linked at the chain-ends to poly(3-hexylthiophene) (P3HT) to give poly[poly(3-hexylthiophene)-block-poly{([1,4]-fullerene)-alt-[1,4-dimethylene-2,5-bis(cyclohexylmethyl ether)phenylene]}] (P3HT-b-PFDP). While normal devices give poor results, inverted architectures result in near 50-fold improvements in performances to a block copolymer efficiency of 2.8% for this novel system. PFDP-b-P3HT is also employed as an additive to P3HT:PCBM bulk heterojunction devices and demonstrates increases from 3.6% to 4.2%, and remarkably gives a stable flat-line efficiency over the time studied.