High Fullerene Content Research Articles

Magnetic iron oxide nanoparticles functionalized with C60 phosphonic acid derivative for catalytic reduction of 4-nitrophenol

Synthesis and self-assembly of C60 fullerene phosphonic acid derivative onto magnetic iron oxide nanoparticles stabilized with oleic acid (OA) for catalytic applications is presented. The as obtained composite nanoparticles were characterized using transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and cyclic voltammetry (CV). As result, introduction of functionalized fullerenes onto surface of magnetic nanoparticles was confirmed. Proposed deposition procedure and use of phosphonic acid anchoring group resulted in high fullerene content in the composite material with approximately 2.6:1 OA to C60 ratio. Afterwards efficient utilization of resulting catalyst in the reduction of 4-nitrophenol using sodium borohydride in water is reported and the kinetics of the reaction have been evaluated. Resulting rate constant was found to be k = 1.54·10−3·s−1. Moreover, magnetic properties of the engineered catalyst allow its simple removal by using external magnetic field and reuse without noticeable loss of efficiency. Presented catalytic nanoparticles may be used not only for synthesis of aromatic amines but also can find application for decontamination of water polluted by 4-nitrophenol.

Single-Material Organic Solar Cells Based on Electrospun Fullerene-Grafted Polythiophene Nanofibers

Highly efficient single-material organic solar cells (SMOCs) based on fullerene-grafted polythiophenes were fabricated by incorporating electrospun one-dimensional (1D) nanostructures obtained from polymer chain stretching. Poly(3-alkylthiophene) chains were chemically tailored in order to reduce the side effects of charge recombination which severely affected SMOC photovoltaic performance. This enabled us to synthesize a donor–acceptor conjugated copolymer with high solubility, molecular weight, regioregularity, and fullerene content. We investigated the correlations among the active layer hierarchical structure given by the inclusion of electrospun nanofibers and the solar cell photovoltaic properties. The results indicated that SMOC efficiency can be strongly increased by optimizing the supramolecular and nanoscale structure of the active layer, while achieving the highest reported efficiency value (PCE = 5.58%). The enhanced performance may be attributed to well-packed and properly oriented polymer ch...

Charge Generation and Recombination in High Fullerene Content Organic Bulk Heterojunction Solar Cells.

Organic bulk heterojunction solar cells with a high fullerene content (larger than 70%) have been studied in this work. The device performances of this kind of solar cell could be tuned by adjusting the blend ratio in the active layer. An appropriate amount of p-type semiconductor in the high fullerene content active blend layer is beneficial for light absorbance and exciton dissociation. The proper energy alignment between the highest occupied molecular orbital of a p-type material and an n-type fullerene derivative has a strong influence on the exciton dissociation efficiency. In addition, the mechanism of photogenerated charge recombination in the solar cells has been identified through intensity-dependent current density–voltage (J–V) measurements and results show that the mechanisms governing the recombination are crucial for solar cell performance.

Synthesis and Characterisation of High Fullerene Content Polymers and Their Use in Organic Photovoltaic Devices

Narrow dispersity polymers with a high tethered fullerene content were synthesised by first polymerising poly(chloromethyl styrene) using reversible addition–fragmentation chain transfer (RAFT) polymerisation and subsequently functionalising them with pristine fullerene. The polymers comprised 52 % by weight fullerene, corresponding to approximately one fullerene per monomer in the polymer with a different morphology to poly(3-hexyl thiophene) (P3HT) : phenyl-C61-butyric acid methyl ester (PCBM) systems. Bulk heterojunctions formed from the polymer tethered fullerene (PTF) with P3HT yielded functioning organic photovoltaic devices with power conversion efficiencies ranging from 0.0030 to 0.22 % as the PTF was increased from 1 : 0.8 to 1 : 1.3. Process optimisation resulted in a maximum efficiency of 0.4 %.

Electrodeposition and Properties of Donor-Acceptor Double-Cable Polythiophene with High Content of Pendant Fulleropyrrolidine Moieties

In this work we report electrochemical copolymerization of thiophene (Th) with thiophene-substituted fulleropyrrolidine (C60-ThFP) on Pt electrode from dichloromethane solution. A structure of the resultant donor-acceptor copolymer with high fullerene content, corresponding to one C60-ThFP per two thiophene units was determined by XPS and FTIR spectroscopy. The ratio of the two monomers in the polymer film was independently determined by electrochemical quartz crystal microbalance. Electroactivity of C60-ThFP and copolymer film in p- and n-doping ranges was studied by cyclic voltammetry. Geometry of a representative fragment of the synthesized copolymer was simulated by means of DFT calculations.

Side-chain fullerene polyesters: a new class of high refractive index polymers

We demonstrate here the synthesis of side-chain fullerene polyesters, a class of soluble high refractive index polymers (n> 1.70).

Photocarrier recombination of polymer/fullerene composites in surface-type photocells

Carrier recombination kinetics is studied by photocurrent measurements of surface-type photocells of polymer/fullerene composites. A quadrimolecular recombination (QR) in the time range of 0.1 to 100 s, which was found for regioregular poly(3-hexylthiophene), is observed in another semicrystalline polymer, poly{2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene} (PBTTT). By measuring photocurrent and transistor action in the same device, suppression of the recombination in the ambipolar region at a high fullerene content is demonstrated. No QR but bimolecular recombination is observed in cells using amorphous-like poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). These results provide further support that the QR is characteristic of high-mobility semicrystalline polymers in which doubly charged states are formed owing to the lamellar structure.

Charge carrier transport and contact selectivity limit the operation of PTB7-based organic solar cells of varying active layer thickness

In this work we study the different electrical loss pathways occurring during the operation of bulk heterojunction solar cells by using a variety of electrical and optical characterization techniques beyond the current density–voltage curve (J–V): Impedance Spectroscopy (IS), Charge Extraction (CE) and Transient Photovoltage (TPV). Two sets of devices are analyzed: the first is based on the donor polymer P3HT, known to provide efficient cells using thick active layers (i.e. 270 nm), and the recently developed PTB7 which offers maximum efficiencies for devices with thinner layers (i.e. 100 nm). Devices fabricated with P3HT:PC60BM are not limited by transport of carriers and large active layer thickness may be used. Importantly, increasing the active layer thickness does not modify the contact selectivity. This is supported by analysis of the diode curve measured in the dark (similar leakage currents) and by capacitance–voltage measurements (similar fullerene content covering the cathode). Under these conditions the current density curve under illumination is mainly defined by the recombination processes taking place in the bulk of the active layer. In contrast, transport of carriers and contact selectivity are both limiting factors for the PTB7:PC60BM system. In this case, best efficiencies are obtained with a low active layer thickness and a high fullerene ratio. Reduced active layer thickness minimizes undesired electrical resistances related to carrier transport through the bulk of the active layer. High fullerene content enhances the amount of fullerene molecules at the cathode leading to decreased leakage currents. Then, the overall device efficiency will be a combination of the recombination kinetics in the bulk of the active layer, undesired resistance to transport of carriers and leakage current present due to low selectivity of the contact. The use of additives has also been explored which enhances charge generation and extraction. Overall, this work provides a comprehensive guide on how to interpret results obtained from some of the most widely used optoelectronic techniques employed to analyse operating devices.

Synthesis, characterization and photovoltaic properties of a new thiophene-based double-cable polymer with pendent fullerene group

In this paper we report the synthesis of a new thiophenic 3-substituted monomer with a plastifying side chain bearing a C60-fullerene moiety at the end. The monomer has been copolymerized with 3-hexylthiophene through the simplest chemical method, namely oxidative polymerization with iron trichloride. The final copolymer, with a high fullerene content (1:1 wt/wt), was fully soluble in common organic solvents and its solubility allowed for its complete physic-chemical characterization. The copolymer thermal behavior was investigated by TGA analysis showing that the incorporation of fullerene has beneficial effects on thermal stability. The fluorescence spectroscopy showed a strong quenching of fluorescence of the copolymer main chains in film, while the AFM analysis confirmed the homogeneous morphology of its films with only very small and uniformly distributed aggregates. The photovoltaic performances of the copolymer and of a film obtained by blending the prepared monomer with poly(3-hexylthiophene) were significantly higher than those obtained using conventional materials and architectures.

Synthesis of Donor−Acceptor Multiblock Copolymers Incorporating Fullerene Backbone Repeat Units

The synthesis of the first example of a block copolymer based on a polymer using fullerene as a backbone repeat subunit is demonstrated. A facile route incorporating the electron acceptor and high fullerene content polymer, poly{(1,4-fullerene)-alt-[1,4-dimethylene-2,5-bis(cyclohexylmethyl ether)phenylene]} (PFDP), with the archetypal electron donor, poly(3-hexylthiophene) (P3HT), into a multiblock copolymer (MBC) structure is presented. α,ω-Bromomethyl-PFDP was prepared by atom-transfer radical addition polymerization (ATRAP) and then reacted with α,ω-phenol-P3HT via a Williamson condensation to yield the MBCs. The lengths of the electron-acceptor and donor polymer blocks could be selected so that the resulting solid state domains were of a size appropriate to organic solar cells. Also it was found that the MBCs gave a wide range of macro-structures, from micelles to well-defined wires, depending on the preparation conditions.

Poly(bisthiophene-carbazole-fullerene) Double-Cable Polymer As New Donor−acceptor Material: Preparation and Electrochemical and Spectroscopic Characterization

A new donor-acceptor dyad, namely, a 3,6-bis(thiophen-2-yl)carbazole derivative bearing a C(60) fullerene as a side group (BTC-F), was prepared and characterized. Electropolymerization of BTC-F leads to the formation of a donor-acceptor double-cable polymer (PBTC-F) with high fullerene content (63 wt %) corresponding to one C(60) per polymer repeat unit. The electronic properties of BTC-F and PBTC-F were studied by electrochemical and spectroscopic techniques. Photoluminescence quenching is observed in diluted solutions of BTC-F compared to the nongrafted monomer BTC indicating that an intramolecular charge transfer takes place between the two components of the dyad. The positions of the HOMO and LUMO levels of the monomer and the polymer were accurately determined by differential pulse voltammetry (DPV). The LUMO energy level of the fullerene moiety in BTC-F lies at 3.7 eV below the vacuum level, i.e., slightly higher than corresponding levels of C(60) and PCBM. DPV characterization of PBTC-F indicates little ground state interaction between the pi-conjugated main chain and the C(60) side groups and a high donor HOMO-acceptor LUMO gap of 1.47 eV.

Well-Defined Fullerene-Containing Homopolymers and Diblock Copolymers with High Fullerene Content and Their Use for Solution-Phase and Bulk Organization

A fullerene-containing norbornene derivative is used for ring-opening metathesis polymerization to synthesize living polymers with high fullerene content. Incorporation of fullerene at every repeat of a small monomer allows high fullerene content and short inter-fullerene distances in a soluble polymer. The living nature of the polymerization also allows the synthesis of diblock copolymers, which exhibit micellar aggregation in solution and phase separation with interpenetrating C60-domains in a thin film upon TEM imaging.

Experimental study of fullerene-PVP polymers by small-angle neutron scattering

Small_angle neutron scattering technique is employed to investigate the structure of fullerene-PVP polymers and the variation of their size with fullerene content. The results indicate that the relative lengths of both mono-molecule and mac romolecule chains in solution with fullerene are shorter than those in pure PVP solution, and the volumes of fullerene-PVP polymers in solution with high fullerene content become much smaller.

SYNTHESIS AND PROPERTIES OF [60]FULLERENE-POLYVINYLPYRIDINE CONJUGATES FOR PHOTOVOLTAIC DEVICES

A two-phase radical polymerization was applied for the synthesis of fullerene-containing poly(4-vinylpyridine), which were used as polyelectrolytes in the fabrication of photovoltaic devices. Two-phase radical polymerization resulted in the products of poly(4-vinyl pyridinated) fullerenes (PVPyF) containing a high fullerene content and poly(4-vinylpyridine) arms of short length. These polyelectrolytes with a C60 content of up to 35% by weight are soluble in organic solvents and water at a low pH. High efficient photoinduced charge transfer in samples of PVPyF and polyanionic polythiophene derivatives fabricated by the electrostatic layer-by-layer deposition technique in producing self-assembled multilayers (SAMs) was demonstrated. As a result, high response to the increase of photoinduced conductivity was observed on the 75 bilayer device of PVPyF-3+/H-PURET− upon irradiation. Photoconductivity was found to increase in more than one order of magnitude from 0.024 to 0.31 S/cm at an applied voltage of 1.0 volt. The sign of short-circuit photocurrent was consistent with electrons flowing from Al electrode towards the ITO modified substrate. †Deceased.

60]Fullerene-Containing Poly(dimethylsiloxane)s: Easy Access to Soluble Polymers with High Fullerene Content

The attachment of [60]fullerene to poly(dimethylsiloxane)s leads to soluble and structurally defined fullerene-containing polymers, exhibiting excellent film-forming properties. Different strategies for the synthesis of polymers, either containing [60]fullerene in the polymer backbone or bearing [60]fullerene as part of the side chains, are described. In the latter case, [60]fullerene contents up to 30 wt % were obtained.