Fullerene Composites Research Articles

Sandwich-Like Graphite–Fullerene Composites with Enhanced Electromagnetic Wave Absorption

Sandwich-like graphite–fullerene composites have been prepared via a simple solution mixing/evaporation method. The complex relative permittivity and permeability of the graphite–fullerene composites in the frequency range from 0.5 GHz to 18 GHz were measured using a vector network analyzer with the reflection/transmission technique. Additionally, the microwave reflection loss of the composites was calculated using the obtained complex microwave electromagnetic parameters. It was found that the microwave loss peaks in the Ku band were dependent on the concentration of fullerene nanoparticles in the composites. Maximum reflection loss of −30 dB was observed between 2 GHz and 8 GHz when the graphite composites were doped with 1 wt.% fullerene. This absorption loss dropped (−24 dB) when the composite contained 3 wt.% fullerene. In addition, the electrical properties of the graphite were independent of the presence of fullerene in the composites. The tunable microwave reflection loss indicates that these graphite–fullerene composites show promise as wideband electromagnetic wave absorption materials.

Ultraviolet light response of electrical and dielectric properties in zinc phthalocyanine and fullerene dispersed liquid crystal composites

Liquid crystal composites form an attractive research area in liquid crystal studies. Among these composites, nematic liquid crystal composited E63 is of particular interest. In the present study, E63 coded liquid crystal composites were dispersed with zinc phthalocyanine (Zn-Pc) and fullerene (C60), and three samples were prepared as E63, E63/Zn-Pc, and E63/Zn-Pc/C60 in indium tin oxide coated cells via capillary action. Later, current and capacitance measurements of the samples were carried out in darkness and under ultraviolet (UV) illumination (365 nm) of 100 mW/cm2 power intensity. It was found that both current and capacitance in the samples are affected by UV light and dispersal of Zn-Pc and C60. Particularly, dispersal of Zn-Pc led to occurrence of photovoltaic properties, which yielded open-circuit voltage of 0.37 V for the E63/Zn-Pc sample. Furthermore, dielectric constant and dielectric anisotropy values were extracted from capacitance values, and UV light was seen to increase the transition frequency of dielectric anisotropy slightly for all samples.

High-toughness/low-friction ductile epoxy coatings reinforced with carbon nanostructures

We present the results of effective reinforcement of epoxy resin matrix with fullerene carbon soot. The optimal carbon soot addition of 1 wt. % results in a toughness improvement of almost 20 times. The optimized soot-epoxy composites also show an increase in tensile elongation of more than 13%, thus indicating a change of the failure mechanism in tension from brittle to ductile. Additionally, the coefficient of friction is reduced from its 0.91 value in plain epoxy resin to 0.15 in the optimized composite. In the optimized composite, the lateral forces during nanoscratching decrease as much as 80% with enhancement of the elastic modulus and hardness by 43% and 94%, respectively. The optimized epoxy resin fullerene soot composite can be a strong candidate for coating applications where toughness, low friction, ductility and light weight are important.

Effect of Blend Composition on Binary Organic Solar Cells Using a Low Band Gap Polymer.

This report investigates the influence of the solution blend composition of binary bulk heterojunction organic solar cells composed of poly(2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H- cyclopenta[2,1-b:3,4-b'dithiophene-2,6-diy]] (PCPDTBT) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM). The blend polymer:fullerene composition was varied from 1:1 (50 wt% PC71 BM) to 2:9 (82 wt% PC71 BM). Increasing the amount of polymer in the blend results in the greatest overall absorption, as the donor material PCPDTBT is the main contributor to absorption. However, high polymer content leads to poor photovoltaic performance. For this material combination, the optimum blend polymer:fullerene composition was found to be 2:7. Increasing the fullerene content in the blend led to a significant improvement in the internal quantum efficiency of devices. This was correlated with an increase of the electron mobility, as the fullerene content was increased. Improved electron transport, leading to more balanced transport between electrons and holes, significantly improved the short circuit current density (Jsc) and fill factor (FF).

Al/C60 Nanocomposites Fabricated by High-Pressure Torsion

Al-2 vol pct fullerene (C60) composites with relative densities of >0.98 are manufactured by high-pressure torsion of ball-milled powders under an applied pressure of 6 GPa. A considerable Al grain refinement to ~53 nm and a homogeneous distribution of fullerenes give rise to a very high hardness of 152 Hv and yield stress of 405 MPa. Nevertheless, the poor tensile ductility due to the low work-hardening rate is achieved.

Synthesis and structural analysis of C60–C70 two-component fullerene nanowhiskers

C60–C70 two-component fullerene nanowhiskers (C60–C70NWs) were synthesized by liquid–liquid interfacial precipitation (LLIP) using various ratios of C70 to C60 and then analyzed using a focused ion beam processing apparatus (FIB-SEM), scanning electron microscopy (SEM), Raman spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, X-ray diffraction (XRD) and high-performance liquid chromatography (HPLC). Both C60 and C70 were saturated in the supernatant solutions with fullerene compositions in the mother solutions ranging from 12.4 mass% C70 to 73.4 mass% C70. C60–C70NWs contained a small amount of rhombohedral phase, indicating polymerization of C60. The solid solubility limit of C70 in the C60 matrix was found to be 13.7 mass%. In addition to fine C60–C70NWs, thick C60–C70 needle-like crystals were formed. The thick C60–C70 needle-like crystals were fractured using a molybdenum probe in the FIB. The fractured surfaces of the C60–C70 needle-like crystals showed modulated structures with chemical compositions characteristic of spinodal decomposition. The activation energy of diffusion was determined to be 37.1kJ/mol.

Interaction between components of poly(methyl methacrylate)-fullerene composite under UV irradiation

The interactions in the poly(methyl methacrylate) (PMMA)-fullerene (C60) system induced by UV irradiation have been studied by the methods of thermodesorption mass spectrometry and UV-Vis spectroscopy. The results are compared to the changes in the character of the kinetics of destruction of the PMMA-C60 composite.

Understanding Triplet Formation Pathways in Bulk Heterojunction Polymer:Fullerene Photovoltaic Devices

Triplet exciton (TE) formation pathways are systematically investigated in prototype bulk heterojunction (BHJ) “super yellow” poly(p‐phenylene vinylene) (SY‐PPV) solar cell devices with varying fullerene compositions using complementary optoelectrical and electrically detected magnetic resonance (EDMR) spectroscopies. It is shown that EDMR spectroscopy allows the unambiguous demonstration of fullerene triplet production in BHJ polymer:fullerene solar cells. EDMR triplet detection under selective photoexcitation of each blend component and of the interfacial charge transfer (CT) state reveals that low lying fullerene TEs are produced by direct intersystem crossing from singlet excitons (SEs). The direct CT‐TE recombination pathway, although energetically feasible, is kinetically suppressed in these devices. However, high energy CT states in the CT manifold can contribute to the population of the fullerene triplet state via a direct CT‐SE conversion. This undesirable energetic alignment could be one of the causes for the severe reduction in photocurrent observed when the open‐circuit voltage of polymer:fullerene solar cells is pushed to 1.0 V or beyond.

Inhibition of thermal degradation of polystyrene by C60 and PCBM: A comparative study

The impact of two different fullerenes (C60 and PCBM) on the thermal stability of the corresponding polystyrene (PS)–fullerene composites was studied over the whole composition range, under nitrogen (N2) and air atmospheres using dynamic thermogravimetric analysis (TGA). The aim of this study was to compare the thermal stabilization effect of C60 and PCBM on polystyrene. Both in nitrogen and in air, all the composites are more stable to thermal decomposition than the pure PS. While in nitrogen the thermal degradation of the PS-fullerene composites occurs in a single step process, in air it occurs in a two-step process in which the first step consists mainly of the degradation of PS, and the second step consists mainly of the fullerene degradation. TGA can be used successfully to determine the amount of C60 and PCBM in the PS composites over the whole composition range. In nitrogen, the residual mass values obtained above 450 °C correlate linearly with the initial amounts of fullerene present in the composites. In air, the residual mass values observed at the temperatures of transition from the first to the second decomposition step also correlate linearly with the initial amounts of fullerene present in the composites. In nitrogen, the thermal stabilization effects of C60 and PCBM are very similar. Conversely, in air PCBM shows a higher thermal stabilization effect than C60 for identical fullerene loadings. We suggest that the improved thermo-oxidative stability of the PCBM composites compared to the C60 composites is due to the fact that, as previously reported in the literature, PCBM disperses better in a PS matrix than C60.

Fundamental aspects of Arn+ SIMS profiling of common organic semiconductors

We investigate the capabilities and limitations of performing (quantitative) in‐depth composition analysis of polymer:fullerene blends, using time‐of‐flight SIMS with large Arn+ clusters. These blends constitute an important class of organic solar cell materials, whose performance and reliability critically depend on the blend's physicochemical properties at the nanoscale. We investigate the effect of Ar cluster size n, kinetic energy E and E/n on the secondary ion and sputter yields and evaluate the Ar beam‐induced damage in these layers. On the basis of this, the ideal experimental conditions are derived that allow us to investigate matrix effects and variations in sputter yields as function of polymer:fullerene compositions. We demonstrate that time‐of‐flight SIMS is capable to retrieve quantitative in‐depth information in common polythiophene, polycarbazole, and fullerene blends. Copyright © 2014 John Wiley & Sons, Ltd.

Iron-oxide-supported nanocarbon in lithium-ion batteries, medical, catalytic, and environmental applications.

Owing to the three different orbital hybridizations carbon can adopt, the existence of various carbon nanoallotropes differing also in dimensionality has been already affirmed with other structures predicted and expected to emerge in the future. Despite numerous unique features and applications of 2D graphene, 1D carbon nanotubes, or 0D fullerenes, nanodiamonds, and carbon quantum dots, which have been already heavily explored, any of the existing carbon allotropes do not offer competitive magnetic properties. For challenging applications, carbon nanoallotropes are functionalized with magnetic species, especially of iron oxide nature, due to their interesting magnetic properties (superparamagnetism and strong magnetic response under external magnetic fields), easy availability, biocompatibility, and low cost. In addition, combination of iron oxides (magnetite, maghemite, hematite) and carbon nanostructures brings enhanced electrochemical performance and (photo)catalytic capability due to synergetic and cooperative effects. This work aims at reviewing these advanced applications of iron-oxide-supported nanocarbon composites where iron oxides play a diverse role. Various architectures of carbon/iron oxide nanocomposites, their synthetic procedures, physicochemical properties, and applications are discussed in details. A special attention is devoted to hybrids of carbon nanotubes and rare forms (mesoporous carbon, nanofoam) with magnetic iron oxide carriers for advanced environmental technologies. The review also covers the huge application potential of graphene/iron oxide nanocomposites in the field of energy storage, biomedicine, and remediation of environment. Among various discussed medical applications, magnetic composites of zero-dimensional fullerenes and carbon dots are emphasized as promising candidates for complex theranostics and dual magneto-fluorescence imaging.

Aqueous Route to Phthalocyanine–Fullerene Composites with Regular Structure

Random mixtures of phthalocyanines (Pcs) with fullerene C60 are currently exploited as active layers in organic solar cells. Therefore, spatially regular Pc–C60 heterostructures, not designed so far, are of great interest as molecularly mixed donor–acceptor phases for further improving the device performance. Here we investigate the prospects to create such heterostructures by fine intermixing of π-rich Pcs with fullerene C60. Specifically, this work reports on the mixing behavior of cobalt tetrakis(3-amino-5-tert-butyl)phthalocyanine (CoPc#) with fullerene C60. A composite film (CoPc#/C60 = 1:2, mol) was prepared by the Langmuir–Schaefer technique from a floating layer with double-decker architecture, where the CoPc# monolayer was interlinked with the C60 submonolayer by the clustered water. This film was structurally analyzed and compared with the CoPc# film used as a reference. The latter film is found to be constructed from the 2-stack dye aggregates, which are assembled in the χ-phase mode, randomly ...

Temperature dependence of the phosphorescence and of the thermally activated delayed fluorescence of 12C70 and 13C70 in amorphous polymer matrices. Is a second triplet involved?

The phosphorescence and thermally activated delayed fluorescence (TADF) lifetimes of 12C70 and 13C70 in two different glassy hydrocarbon polymers, one aliphatic (cyclic polyolefin) and one aromatic (polystyrene), were measured between −200 and 100 ºC. The temperature dependence of the lifetimes is equally well described by a three-state mechanism (ground state, S0, and two excited states in thermal equilibrium, T1 and S1, the lifetime of T1 being temperature dependent) and by a four-state mechanism (ground state, S0, and three excited states in thermal equilibrium, T1, T2 and S1, all with temperature-independent lifetimes). The estimated S1–T1 and T2–T1 energy gaps (four-state mechanism) are in good agreement with spectroscopic measurements. These and the determined quantum yield of triplet formation, 0.997 ± 0.001, are found to be essentially independent of the polymer matrix and of the isotopic composition of the fullerene. On the other hand, the lifetimes of both T1 and T2 (four-state mechanism) are weakly dependent on the polymer matrix but strongly vary with the fullerene isotopic composition, nearly doubling when going from 12C70 to 13C70. A parameter useful for the characterization of TADF, the on-set temperature T0, is also introduced.

Visible light responsive titanium dioxide–cyclodextrin–fullerene composite with reduced charge recombination and enhanced photocatalytic activity

Titanium dioxide (TiO2)–fullerene (C60) composite is prepared from TiO2 and β-cylcodextrin (CD) encapsulated C60 using the solar light irradiation. The absorption of the composite extends to the visible light region due to the charge transfer from CD and C60 to TiO2. The composite shows reduced charge recombination compared to that of the bare TiO2 and TiO2/CD. The rate constant values for the photodegradation reactions of methylene blue and 4-chlorophenol (4-CP) are significantly higher (∼2–5 times) for the composites with 0.5 and 1.5 wt.% C60 compared to that of the bare TiO2. Photocatalytic studies in the presence of scavengers reveal that the composites produce higher amount of reactive oxygen species (ROS). The enhanced photocatalytic activity of the composites is attributed to the visible light responsiveness, reduced charge recombination and increased formation of ROS. The photodegradation of 4-CP is significantly faster in the presence of the composite with 1.5 wt.% C60 and is attributed to the synergistic effect of higher adsorption and increased ROS formation. The ROS formation by C60 is possible because of the non-aggregated state of C60 molecules in the composite and is assigned to the method which employs CD molecules to disperse C60 in the composite.

Modifications in Morphology Resulting from Nanoimprinting Bulk Heterojunction Blends for Light Trapping Organic Solar Cell Designs

Nanoimprinting the photoactive layer of bulk heterojunction (BHJ) organic solar cells is a promising technique for enhancing device performance via improved light absorption. Here, we demonstrate that imprinting poly(3-hexylthiophene) (P3HT) and fullerene BHJ blends leads to adverse morphological changes within the photoactive nanopattern which have been previously overlooked. In particular, nanoimprinting induces a factor of 2 difference in polymer:fullerene composition between the nanopattern posts and interconnecting flash layer that inadvertently moves the composition outside the range for optimal performance. This occurs because of the strong tendency of regioregular P3HT to crystallize since imprinting blends based on amorphous regiorandom P3HT have uniform nanopattern composition. Based on these results, we outline promising design strategies, such as nanoimprinting amorphous polymers, to serve as guidelines for fabricating high-performance nanopatterned BHJ solar cells capable of maximized light absorption.

Synthesis of fullerenes in a high-frequency arc plasma under elevated helium pressure

We show that in a carbon–helium high-frequency (66kHz) arc discharge the fullerene yield and composition can be controlled by changing the helium pressure. By emission spectroscopy we could derive the excitation temperature within the arc. We found that the radial temperature gradient of the arc plasma increases with increasing pressure. We further found that with increasing pressure the yield of fullerenes reaches a maximum of 12.6wt.% at 0.12MPa pressure and in the range from 0.16 to 0.38MPa the fullerene content in the carbon soot stays within the limits of 7.2–7.0wt.%. The content of С70 and higher fullerenes relative to the total amount of extractable fullerenes increases with pressure. Our results suggest that in the carbon–helium plasma fullerenes are mainly formed in a top-down process by the decay and annealing of large, hot precursor carbon molecules.

Relating Recombination, Density of States, and Device Performance in an Efficient Polymer:Fullerene Organic Solar Cell Blend

AbstractWe explore the interrelation between density of states, recombination kinetics, and device performance in efficient poly[4,8‐bis‐(2‐ethylhexyloxy)‐benzo[1,2‐b:4,5‐b']dithiophene‐2,6‐diyl‐alt‐4‐(2‐ethylhexyloxy‐1‐one)thieno[3,4‐b]thiophene‐2,6‐diyl]:[6,6]‐phenyl‐C71‐butyric acid methyl ester (PBDTTT‐C:PC71BM) bulk‐heterojunction organic solar cells. We modulate the active‐layer density of states by varying the polymer:fullerene composition over a small range around the ratio that leads to the maximum solar cell efficiency (50–67 wt% PC71BM). Using transient and steady‐state techniques, we find that nongeminate recombination limits the device efficiency and, moreover, that increasing the PC71BM content simultaneously increases the carrier lifetime and drift mobility in contrast to the behavior expected for Langevin recombination. Changes in electronic properties with fullerene content are accompanied by a significant change in the magnitude or energetic separation of the density of localized states. Our comprehensive approach to understanding device performance represents significant progress in understanding what limits these high‐efficiency polymer:fullerene systems.

Shape and diameter control of C60 fullerene micro-stains by evaporation of aqueous SDS–fullerene dispersion drops

The effect of the surface free energy of substrates such as glass slide, polymethyl methacrylate, polystyrene, polypropylene and Teflon-FEP was investigated on the shape and diameter of fullerene (C60) stains which were obtained by evaporation of aqueous sodium dodecyl sulfate/fullerene dispersion drops having different SDS/C60 fullerene compositions and different drop volumes. It was found that the surface free energy of the substrates was the most important parameter to control the shape and the diameters of the formed SDS/C60 fullerene deposits and a good linear relationship was obtained between the stain diameter and surface free energy of the substrates. Uniform circular fullerene/SDS deposits were obtained on polystyrene surfaces.

Comparison of the electrochemical properties of thin films of MWCNTs/C60-Pd, SWCNTs/C60-Pd and ox-CNOs/C60-Pd

This work describes the study of the electrochemical properties of fullerene polymer composites, C60-Pd, and different carbon nanostructures, such as single walled carbon nanotubes, multi walled carbon nanotubes and carbon nanoonions, as potential electrode materials for supercapacitors. The carbon nanostructures were deposited onto a bare gold disc electrode by a vapor deposition process. In the next step, the fullerene was electrochemically polymerized under cyclic voltammetric conditions. The obtained composites are electrochemically active at negative potentials due to the reduction of the fullerene moieties. The voltammetric response corresponding to this electrochemical process depends on the type of nanostructure and the amount of material deposited at the electrode surface. Such systems exhibit promising electrochemical properties. The highest capacitance of about 1000Fg−1, with respect to mass of polymer, was obtained for the SWCNTs/C60-Pd composite. This value is about four times higher compared to the capacitance of the polymer deposited on a bare gold electrode surface. Lower values of the specific capacitance were obtained for composites containing other MWCNTs and ox-CNOs. For the C60-Pd/ox-CNOs composites the highest values of the specific capacitance were found to be about 280Fg−1.

Molecular Intercalation and Cohesion of Organic Bulk Heterojunction Photovoltaic Devices

AbstractThe phase separated bulk heterojunction (BHJ) layer in BHJ polymer:fullerene organic photovoltaic devices (OPV) are mechanically weak with low values of cohesion. Improved cohesion is important for OPV device thermomechanical reliability. BHJ devices are investigated and how fullerene intercalation within the active layer affects cohesive properties in the BHJ is shown. The intercalation of fullerenes between the side chains of the polymers poly(3,3″′‐didocecyl quaterthiophene) (PQT‐12) and poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene (pBTTT) is shown to enhance BHJ layer cohesion. Cohesion values range from ≈1 to 5 J m−2, depending on the polymer:fullerene blend, processing conditions, and composition. Devices with non‐intercalated BHJ layers are found to have significantly reduced values of cohesion. The resulting device power conversion efficiencies (PCE) are also investigated and correlated with the device cohesion.