Photovoltaic cells based on polythiophenes carrying lateral phenyl groups

Highly regioregular poly[3-(4-octylphenylthiophene)] (POPT) was prepared to study the influence of phenyl groups as substituents on photovoltaic and thermal properties with respect to poly(3-hexylthiophene) (P3HT). The UV-visible absorption spectra of spin-coated films of POPT exhibited an extended absorption towards the near infrared. Differential scanning calorimetry showed the poor tendency of POPT to crystallise. In order to retain the extension in absorption and increase crystallinity, poly(3-hexylthiophene)-block-poly(3-tolylthiophene) (P3HT-b-P3TT) samples with varying ratios of P3HT and P3TT were prepared. Thermal fractionation by successive self-nucleation and annealing indicated that crystallites of P3HT were influenced by the P3TT block within the copolymers. Thermogravimetric analysis showed that thermal stabilities increased with increasing fractions of phenyl groups. Photovoltaic results of these materials blended with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) are presented and discussed. © 2007 Elsevier B.V. All rights reserved

Diblock and random Donor/Acceptor "Double Cable" polythiophene copolymers via the GRIM method

International audienceIn this paper, we report the synthesis via the Grignard metathesis method (GRIM) of donor/ acceptor double cable copolymers with diblock and random sequences, where the conjugated polythiophene backbone is substituted with hexyl chains and with alkyl chains bearing fullerene. First, the monomers 2,5-dibromo-3-hexylthiophene and 2,5-dibromo-3-(l,3-dioxa-2-octyl)thiophene were randomly copolymerized and yielded after the grafting of fullerene C 60 the double cable CoPTR-C. Second, the same monomers were used to synthesize a diblock copolymer with a block made from a random copolymerization of both monomers while the second block is pure poly(3-hexylthiophene). After the grafting of fullerene, the block double cable CoPTBl-C was obtained. Both double cable copolymers were investigated through various characterization methods. NMR ID and 2D experiments allowed the full structural characterization and the determination of the final composition of the copolymers. The thermal behavior was investigated by TGA and DSC measurements, indicating that the incorporation of fullerene increased the thermal stability of the materials. The optical properties of these double cable copolymers were investigated by UV-visible absorption and fluorescence spectroscopy. The results showed no interaction at ground-state between the donor and acceptor moieties and a quenching of fluorescence of the polythiophene main chains in solution. AFM analysis on drop-casted films showed the dependence of the morphology of the double cable systems (random or diblock) on the aggregation. © 2008 American Chemical Society

Thermally Stable Bulk Heterojunctions Solar Cells Based on Cross-Linkabble Acrylate-Functionalized Polythiophene Diblock Copolymers

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Thermally Stable Bulk Heterojunction Solar Cells Based on Cross-Linkable Acrylate-Functionalized Polythiophene Diblock Copolymers

We report on the synthesis of new thermally cross-linkable all-conjugated diblock copolymers composed of a poly(3-hexylthiophene) (P3HT) block and an acrylate-functionalized polythiophene block. These copolymers are then used in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and their photovoltaic performances are compared with standard P3HT/PCBM devices. Thermal cross-linking of the functional copolymers/PCBM blends is performed to improve the thermal stability of the active layer. BHJ photovoltaic cells with cross-linkable copolymers and PCBM show initial power conversion efficiencies slightly lower than that of P3HT devices. However, solar cells with cross-linkable copolymers retain more than 85% of their initial power efficiency value after 165 h of thermal annealing (accelerated aging test), whereas the same devices with P3HT retain less than 65% of their initial power efficiency. This improvement of the thermal stability of BHJ photovoltaic cells is the result of the polymer network that hampers PCBM diffusion and phase separation, as confirmed with TEM and AFM analysis of the microscopic morphology. Such an improvement is mostly observed when using a cross-linkable P3HT with a short spacer between the acrylate group and the polythiophene backbone

Regioregular phenyl and phenoxy substituted polythiophenes for bulk heterojunction solar cells

International audiencePoly[3-(4-octylphenyl) thiophene] (PORT) and poly[3-(4-octylphenoxy) thiophene] (POPOT) with high head-to-tall regioregularitlis have been synthesised and photovoltaic properties have been investigated. POPT-blend-PCBM exhibits an interesting behaviour in bulk heterojunction whereas POPOT presents poor photovoltaic performances. UV-visible absorption and AFM images of the blends are presented to explain these results. Copyright © 2008 WILEY-VCH Verlag GmbH & Co. KGaA

Synthesis and characterization of high molecular weight and regioregular poly[3-(4-octylphenyl)thiophene] for bulk heterojunction photovoltaic cells

Various poly[3-(4-octylphenyl)thiophene]s (POPTs) were prepared either by oxidative polymerisation or by chain-growth Grignard metathesis (GRIM). In accordance with previous results, the former polymerisation yielded polydisperse POPT. The method based on the GRIM reaction made possible the preparation of medium and higher molecular weight polymers with lower polydispersities. The POPTs were found to have band-gaps of ca. 1.7 eV. The photovoltaic characteristics of POPTs-blend-[6,6]-phenyl C61 butyric acid methyl ester (PCBM) composites under AM 1.5 conditions in standard ITO/PEDOT-blend-PSS/POPT-blend-PCBM/LiF/Al solar cells were studied. It was found that POPT prepared via GRIM could deliver greater efficiencies than its equivalent prepared by oxidative polymerisation. It is expected that access to even higher molecular weight POPTs may improve the efficiencies of such devices

Effect of molar mass and regioregularity on the photovoltaic properties of a reduced bandgap phenyl-substituted polythiophene

International audienceAmong the numerous reduced bandgap polymers currently being developed, poly[3-(4-octylphenyl)thiophene)]s (POPT) may present attractive properties for organic solar cells due to its facile preparation and improved absorption with respect to poly(3-hexylthiophene). This article appraises methods of preparation, including the use of diphenyl ether as a reaction medium, and discusses the effects of variations in molar masses, from about 3200 to 65,000 g mol -1 and regioregularity on its optoelectronic properties. The photovoltaic properties of POPT with [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) in bulk heterojunction devices are also discussed in the light of morphological variations, as indicated by atomic force microscopy characterizations. With an initial screening of conditions, namely POPT:PCBM ratios and deposition solvent, a power conversion efficiency of 1.58% was obtained using a relatively high molar mass POPT sample

Thermally stable bulk heterojunction solar cells based on cross-linkable acrylate-functionalized polythiophene diblock copolymers

We report on the synthesis of new thermally cross-linkable all-conjugated diblock copolymers composed of a poly(3-hexylthiophene) (P3HT) block and an acrylate-functionalized polythiophene block. These copolymers are then used in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and their photovoltaic performances are compared with standard P3HT/PCBM devices. Thermal cross-linking of the functional copolymers/PCBM blends is performed to improve the thermal stability of the active layer. BHJ photovoltaic cells with cross-linkable copolymers and PCBM show initial power conversion efficiencies slightly lower than that of P3HT devices. However, solar cells with cross-linkable copolymers retain more than 85% of their initial power efficiency value after 165 h of thermal annealing (accelerated aging test), whereas the same devices with P3HT retain less than 65% of their initial power efficiency. This improvement of the thermal stability of BHJ photovoltaic cells is the result of the polymer network that hampers PCBM diffusion and phase separation, as confirmed with TEM and AFM analysis of the microscopic morphology. Such an improvement is mostly observed when using a cross-linkable P3HT with a short spacer between the acrylate group and the polythiophene backbone