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Showing papers on "Fullerene published in 2009"


Journal ArticleDOI
TL;DR: In this article, the vertical phase separation of spin-coated poly(3-hexylthiophene) (P3HT):fullerene derivative blends was investigated using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM).
Abstract: A method which enables the investigation of the buried interfaces without altering the properties of the polymer films is used to study vertical phase separation of spin-coated poly(3-hexylthiophene) (P3HT):fullerene derivative blends. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analysis reveals the P3HT enrichment at the free (air) surfaces and abundance of fullerene derivatives at the organic/substrate interfaces. The vertical phase separation is attributed to the surface energy difference of the components and their interactions with the substrates. This inhomogeneous distribution of the donor and acceptor components significantly affects photovoltaic device performance and makes the inverted device structure a promising choice.

676 citations


Journal ArticleDOI
TL;DR: This work clears a path towards higher PCEs in OPV devices by demonstrating that high-yield charge separation can occur with OPV systems that have a reduced donor/acceptor lowest unoccupied molecular orbital energy offset.
Abstract: A limiting factor of the power conversion efficiencies of organic photovoltaic devices is low voltage output Methano derivatives of the trimetallic endohedral fullerene Lu3N@C80 have now been synthesized and used as the acceptor in organic photovoltaics The open circuit voltage of the devices is significantly above those made using alternative fullerenes So far, one of the fundamental limitations of organic photovoltaic (OPV) device power conversion efficiencies (PCEs) has been the low voltage output caused by a molecular orbital mismatch between the donor polymer and acceptor molecules Here, we present a means of addressing the low voltage output by introducing novel trimetallic nitride endohedral fullerenes (TNEFs) as acceptor materials for use in photovoltaic devices TNEFs were discovered in 1999 by Stevenson et al 1; for the first time derivatives of the TNEF acceptor, Lu3N@C80, are synthesized and integrated into OPV devices The reduced energy offset of the molecular orbitals of Lu3N@C80 to the donor, poly(3-hexyl)thiophene (P3HT), reduces energy losses in the charge transfer process and increases the open circuit voltage (Voc) to 260 mV above reference devices made with [6,6]-phenyl-C61-butyric methyl ester (C60-PCBM) acceptor PCEs >4% have been observed using P3HT as the donor material This work clears a path towards higher PCEs in OPV devices by demonstrating that high-yield charge separation can occur with OPV systems that have a reduced donor/acceptor lowest unoccupied molecular orbital energy offset

577 citations


Journal ArticleDOI
17 Aug 2009-Small
TL;DR: Coleman and coworkers have successfully demonstrated the concept of solvent–graphene interactions at least comparable to those existing between the stacked graphenes in graphite using N-methylpyrrolidone, N,N-dimethylacetamide, g-butyrolactone, and benzyl benzoate as inputs.
Abstract: Following the astonishing discoveries of fullerenes and carbon nanotubes in earlier decades, the rise of graphene has recently triggered an exciting new area in the field of carbon nanoscience with continuously growing academic and technological impetus. Currently, several methods have been proposed to prepare graphenes, such as micromechanical cleavage, thermal annealing of SiC, chemical reduction of graphite oxide, intercalative expansion of graphite, bottom-up growth, chemical vapor deposition, and liquid-phase exfoliation. Especially this latter top-down approach is very appealing from a chemist’s point of view for the following reasons: i) it is direct, simple, and benign producing graphenes just by solvent treatment of graphite powders, and ii) the as-obtained sheets form colloidal dispersions in the solvents used for the exfoliation, thereby enabling their manipulation into various processes, like mixing, blending, casting, impregnation, spin-coating, or functionalization. The key parameter for suitable solvents is that the solvent–graphene interactions must be at least comparable to those existing between the stacked graphenes in graphite. To that end, Coleman and coworkers have successfully demonstrated this concept using N-methylpyrrolidone, N,N-dimethylacetamide, g-butyrolactone, 1,3-dimethyl-2-imidazolidinone, and benzyl benzoate as

513 citations


Journal ArticleDOI
TL;DR: Results show that covalently functionalizing graphene with the reverse saturable absorption chromospheres porphyrin and fullerene can enhance the nonlinear optical performance in the nanosecond regime.
Abstract: The nonlinear optical properties of two novel graphene nanohybrid materials covalently functionalized with porphyrin and fullerene were investigated by using the Z-scan technique at 532 nm in the nanosecond and picosecond time scale. Results show that covalently functionalizing graphene with the reverse saturable absorption chromospheres porphyrin and fullerene can enhance the nonlinear optical performance in the nanosecond regime. The covalently linked graphene nanohybrids offer performance superior to that of the individual graphene, porphyrin, and fullerene by combination of a nonlinear mechanism and the photoinduced electron or energy transfer between porphyrin or fullerene moiety and graphene.

435 citations


Journal ArticleDOI
TL;DR: In this paper, X-ray diffraction is used to demonstrate the formation of stable, well-ordered bimolecular crystals of fullerene intercalated between the side-chains of the semiconducting polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene).
Abstract: The performance of polymer:fullerene bulk heterojunction solar cells is heavily influenced by the interpenetrating nanostructure formed by the two semiconductors because the size of the phases, the nature of the interface, and molecular packing affect exciton dissociation, recombination, and charge transport. Here, X-ray diffraction is used to demonstrate the formation of stable, well-ordered bimolecular crystals of fullerene intercalated between the side-chains of the semiconducting polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene. It is shown that fullerene intercalation is general and is likely to occur in blends with both amorphous and semicrystalline polymers when there is enough free volume between the side-chains to accommodate the fullerene molecule. These findings offer explanations for why luminescence is completely quenched in crystals much larger than exciton diffusion lengths, how the hole mobility of poly(2-methoxy-5-(3′,7′-dimethyloxy)-p-phylene vinylene) increases by over 2 orders of magnitude when blended with fullerene derivatives, and why large-scale phase separation occurs in some polymer:fullerene blend ratios while thermodynamically stable mixing on the molecular scale occurs for others. Furthermore, it is shown that intercalation of fullerenes between side chains mostly determines the optimum polymer:fullerene blending ratios. These discoveries suggest a method of intentionally designing bimolecular crystals and tuning their properties to create novel materials for photovoltaic and other applications.

412 citations


Journal ArticleDOI
TL;DR: In this paper, the preparation of 27 different derivatives of C60 and C70 fullerenes possessing various aryl (heteroaryl) and/or alkyl groups that are appended to the fullerene cage via a cyclopropane moiety and their use in bulk heterojunction polymer solar cells is reported.
Abstract: The preparation of 27 different derivatives of C60 and C70 fullerenes possessing various aryl (heteroaryl) and/or alkyl groups that are appended to the fullerene cage via a cyclopropane moiety and their use in bulk heterojunction polymer solar cells is reported. It is shown that even slight variations in the molecular structure of a compound can cause a significant change in its physical properties, in particular its solubility in organic solvents. Furthermore, the solubility of a fullerene derivative strongly affects the morphology of its composite with poly(3-hexylthiophene), which is commonly used as active material in bulk heterojunction organic solar cells. As a consequence, the solar cell parameters strongly depend on the structure and the properties of the fullerene-based material. The power conversion efficiencies for solar cells comprising these fullerene derivatives range from negligibly low (0.02%) to considerably high (4.1%) values. The analysis of extensive sets of experimental data reveals a general dependence of all solar cell parameters on the solubility of the fullerene derivative used as acceptor component in the photoactive layer of an organic solar cell. It is concluded that the best material combinations are those where donor and acceptor components are of similar and sufficiently high solubility in the solvent used for the deposition of the active layer.

361 citations


Journal ArticleDOI
TL;DR: In this paper, the nonlinear optical properties of graphene oxide (GO) were investigated at 532 nm in nanosecond and picosecond regimes, and it was shown that two-photon absorption dominates nonlinear absorption process of GO in the case of 2D pulses.
Abstract: The nonlinear optical properties of graphene oxide (GO) were investigated at 532 nm in nanosecond and picosecond regimes. Results show that two-photon absorption dominates nonlinear absorption process of GO in the case of picosecond pulses, while excited state nonlinearities play an important role in the case of nanosecond pulses. Additionally, we compared nonlinear optical properties of three different dimensional carbon-based materials (two-dimensional graphene, one-dimensional carbon nanotube, and zero-dimensional fullerene) in nanosecond and picosecond regimes, respectively. The nonlinear mechanism of GO is distinctly different from nonlinear scattering of carbon nanotube and excited state nonlinearity of fullerene.

338 citations


Journal ArticleDOI
TL;DR: The intercalated blends, which exhibit optimal solar-cell performance at 1:4 polymer:fullerene by weight, have better photoluminescence quenching and lower absorption than the nonintercalations, which optimize at1.1:1.
Abstract: We demonstrate that intercalation of fullerene derivatives between the side chains of conjugated polymers can be controlled by adjusting the fullerene size and compare the properties of intercalated and nonintercalated poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene (pBTTT):fullerene blends. The intercalated blends, which exhibit optimal solar-cell performance at 1:4 polymer:fullerene by weight, have better photoluminescence quenching and lower absorption than the nonintercalated blends, which optimize at 1:1. Understanding how intercalation affects performance will enable more effective design of polymer:fullerene solar cells.

256 citations


Journal ArticleDOI
TL;DR: This Review focuses on recent work on stabilization of non-IPR fullerenes, including theoretical and empirical principles, experimental methods, and molecular structures of fused-pentagon fullererenes characterized so far.
Abstract: The most stable fullerenes obey the isolated-pentagon rule (IPR): hexagons of carbon atoms entirely surround pentagons to minimize strain. Recently, some examples of fused-pentagon fullerenes have been reported and this Review summarizes current work to stabilize non-IPR fullerenes. The isolated pentagon rule (IPR) is now widely accepted as a general rule for determining the stability of all-carbon fullerene cages composed of hexagons and pentagons. Fullerenes that violate this rule have been deemed too reactive to be synthesized. The stabilization of non-IPR endohedral fullerenes depends on charge transfer from the encapsulated metal clusters (endoclusters) to fullerene cages, the electronic properties of empty all-carbon cages, the matching size and geometries of fullerene and endocluster, as well as the strong coordination of the metal ions to fused pentagons. The stability of non-IPR exohedral fullerenes can be rationalized primarily by both the 'strain-relief' and 'local-aromaticity' principles. This Review focuses on recent work on stabilization of non-IPR fullerenes, including theoretical and empirical principles, experimental methods, and molecular structures of fused-pentagon fullerenes characterized so far. The special chemical properties of non-IPR fullerenes that distinguish them from IPR-satisfying ones are also emphasized.

234 citations


Journal ArticleDOI
TL;DR: In this article, the authors induced sublimation of suspended few-layer graphene by in situ Joule-heating inside a transmission electron microscope and observed a fractal-like “coastline” morphology.
Abstract: We induced sublimation of suspended few-layer graphene by in situ Joule-heating inside a transmission electron microscope. The graphene sublimation fronts consisted of mostly {1100} zigzag edges. Under appropriate conditions, a fractal-like “coastline” morphology was observed. Extensive multiple-layer reconstructions at the graphene edges led to the formation of unique carbon nanostructures, such as sp2-bonded bilayer edges (BLEs) and nanotubes connected to BLEs. Flat fullerenes/nanopods and nanotubes tunneling multiple layers of graphene sheets were also observed. Remarkably, >99% of the graphene edges observed during sublimation are BLEs rather than monolayer edges (MLEs), indicating that BLEs are the stable edges in graphene at high temperatures. We reproduced the “coastline” sublimation morphologies by kinetic Monte Carlo (kMC) simulations. The simulation revealed geometrical and topological features unique to quasi-2-dimensional (2D) graphene sublimation and reconstructions. These reconstructions were enabled by bending, which cannot occur in first-order phase transformations of 3D bulk materials. These results indicate that substrate of multiple-layer graphene can offer unique opportunities for tailoring carbon-based nanostructures and engineering novel nano-devices with complex topologies.

224 citations


Journal ArticleDOI
TL;DR: In this article, two amorphous fullerenes, TPA-PCBM and MFPCBM, have been developed as efficient electron acceptors to induce a highly stable morphology of active layer in polymer photovoltaic devices.
Abstract: Two amorphous fullerenes, TPA-PCBM and MF-PCBM, have been developed as efficient electron acceptors to induce a highly stable morphology of active layer in polymer photovoltaic devices. The power conversion efficiency (PCE) of devices using both materials show no degradation, even after 10 h annealing at 150 °C.

Journal ArticleDOI
TL;DR: Investigation of the stability and aggregation kinetics of two different suspensions of fullerene (C60) nanoparticles and their relation to nanoparticle charge (electrokinetic) properties shows that both fulleren nanoparticles are more negatively charged and stable at higher pH conditions, suggesting that dissociation of surface functional groups contributes to surface charge for both nanoparticles.
Abstract: The stability and aggregation kinetics of two different suspensions of fullerene (C60) nanoparticles and their relation to nanoparticle charge (electrokinetic) properties were investigated. The two synthesis methods employed—a solvent exchange method involving sonication of fullerene initially dissolved in toluene and prolonged stirring of bulk fullerene in water—produce negatively charged fullerene nanoparticles. With an increase in electrolyte (KCl) concentration, the electrophoretic mobilities of both fullerene nanoparticles became less negative, while the corresponding aggregation rates increased until maximum rates were reached at their respective critical coagulation concentrations. This behavior is consistent with the classic Derjaguin−Landau−Verwey−Overbeek (DLVO) theory for the stability of charged colloidal particles. The nanoparticles prepared by prolonged stirring of bulk fullerene in water were much more stable than those prepared by sonication in toluene, as evident from their significantly ...

Journal ArticleDOI
Xiaoyan Zhang1, Yi Huang1, Yan Wang1, Yanfeng Ma1, Zunfeng Liu1, Yongsheng Chen1 
01 Jan 2009-Carbon
TL;DR: In this paper, a graphene-C60 hybrid material was synthesized using a chemical coupling method between graphene oxide and pyrrolidine fullerene, which was verified by Fourier transform infrared spectroscopy, thermal gravimetric analysis and high-resolution transmission electron microscopy.

Journal ArticleDOI
TL;DR: The Ca-coated boron fullerenes and nanotubes proposed in this work are favorable for reversible adsorption and desorption of hydrogen at ambient conditions.
Abstract: A comprehensive study was performed on hydrogen adsorption and storage in Ca-coated boron fullerenes and nanotubes by means of density functional computations. Ca strongly binds to boron fullerene and nanotube surfaces due to charge transfer between Ca and the B substrate. Accordingly, Ca atoms do not cluster on the surface of the boron substrate, while transition metals (such as Ti and Sc) persist in clustering on the B(80) surface. B(80) fullerene coated with 12 Ca atoms can store up to 60 H(2) molecules with a binding energy of 0.12-0.40 eV/H(2), corresponding to a gravimetric density of 8.2 wt %, while the hydrogen storage capacity in a (9,0) B nanotube is 7.6 wt % with a binding energy of 0.10-0.30 eV/H(2). The Ca-coated boron fullerenes and nanotubes proposed in this work are favorable for reversible adsorption and desorption of hydrogen at ambient conditions.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate that the temperature in the condensation zone determines the formation pathway of carbonaceous particles and fullerene fragments or complete fullerenes equip the nucleating particles.
Abstract: Carbonaceous grains represent a major component of cosmic dust. In order to understand their formation pathways, they have been prepared in the laboratory by gas-phase condensation reactions such as laser pyrolysis and laser ablation. Our studies demonstrate that the temperature in the condensation zone determines the formation pathway of carbonaceous particles. At temperatures lower than 1700 K, the condensation by-products are mainly polycyclic aromatic hydrocarbons (PAHs) that are also the precursors or building blocks for the condensing soot grains. The low-temperature condensates contain PAH mixtures that are mainly composed of volatile three to five ring systems. At condensation temperatures higher than 3500 K, fullerene-like carbon grains and fullerene compounds are formed. Fullerene fragments or complete fullerenes equip the nucleating particles. Fullerenes can be identified as soluble components. Consequently, condensation products in cool and hot astrophysical environments such as cool and hot asymptotic giant branch stars or Wolf-Rayet stars should be different and should have distinct spectral properties.

Journal ArticleDOI
TL;DR: In this article, high-resolution STM images of monolayers comprising oligothiophene and fullerene molecular semiconductors reveal details of molecular-scale phase separation and ordering with potential implications for the design of organic electronic devices, in particular future bulk heterojunction solar cells.
Abstract: Scanning tunneling microscopy (STM) of monolayers comprising oligothiophene and fullerene molecular semiconductors reveals details of their molecular-scale phase separation and ordering with potential implications for the design of organic electronic devices, in particular future bulk heterojunction solar cells. Prochiral terthienobenzenetricarboxylic acid (TTBTA) self-assembles at the solution/graphite interface into either a porous chicken wire network linked by dimeric hydrogen bonding associations of COOH groups (R2 (8)) or a close-packed network linked in a novel hexameric hydrogen bonding motif (R6 (24)). Analysis of high-resolution STM images shows that the chicken wire phase is racemically mixed, whereas the close-packed phase is enantiomerically pure. The cavities of the chicken wire structure can efficiently host C60 molecules, which form ordered domains with either one, two, or three fullerenes per cavity. The observed monodisperse filling and long-range co-alignment of fullerenes is described in terms of a combination of an electrostatic effect and the commensurability between the graphite and molecular network, which leads to differentiation of otherwise identical adsorption sites in the pores.

Journal ArticleDOI
TL;DR: This work demonstrates, for the first time, that extended pi-systems with curvatures exceeding those of the most curved stable fullerenes and carbon nanotubes can be prepared by ordinary laboratory methods in solution, without recourse to high-temperature gas phase methods, such as flash vacuum pyrolysis.
Abstract: Syntheses and X-ray crystal structures are reported for all seven members of the indenocorannulene family, comprising indenocorannulene, both isomers of diindenocorannulene, both isomers of triindenocorannulene, tetraindenocorannulene, and pentaindenocorannulene. With each additional indenoannulation, the pyramidalization of the trigonal carbon atoms at the hub of the corannulene increases. Five of the seven indenocorannulenes contain carbon atoms at the hub that are actually more pyramidalized than the carbon atoms of C60. This work demonstrates, for the first time, that extended π-systems with curvatures exceeding those of the most curved stable fullerenes and carbon nanotubes can be prepared by ordinary laboratory methods in solution, without recourse to high-temperature gas phase methods, such as flash vacuum pyrolysis. This proof of principle presages the days when scientists will be able to synthesize isomerically pure fullerenes and single-chirality nanotubes by well-understood, controlled chemical...

Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate that the temperature in the condensation zone determines the formation pathway of carbonaceous particles and fullerene fragments or complete fullerenes equip the nucleating particles.
Abstract: Carbonaceous grains represent a major component of cosmic dust. In order to understand their formation pathways, they have been prepared in the laboratory by gas-phase condensation reactions such as laser pyrolysis and laser ablation. Our studies demonstrate that the temperature in the condensation zone determines the formation pathway of carbonaceous particles. At temperatures lower than 1700 K, the condensation by-products are mainly polycyclic aromatic hydrocarbons (PAHs), that are also the precursors or building blocks for the condensing soot grains. The low-temperature condensates contain PAH mixtures that are mainly composed of volatile 3-5 ring systems. At condensation temperatures higher than 3500 K, fullerene-like carbon grains and fullerene compounds are formed. Fullerene fragments or complete fullerenes equip the nucleating particles. Fullerenes can be identified as soluble components. Consequently, condensation products in cool and hot astrophysical environments such as cool and hot AGB stars or Wolf Rayet stars should be different and should have distinct spectral properties.

Journal ArticleDOI
TL;DR: A new concept is described for methane and hydrogen storage materials involving the incorporation of magnesium-decorated fullerenes within metal-organic frameworks (MOFs) using a novel approach underpinned by surface potential energies developed from Lennard-Jones parameters, which predicts exceptional performance for the Mg-C(60)@MOF family of materials.
Abstract: A new concept is described for methane and hydrogen storage materials involving the incorporation of magnesium-decorated fullerenes within metal−organic frameworks (MOFs). The system is modeled using a novel approach underpinned by surface potential energies developed from Lennard-Jones parameters. Impregnation of MOF pores with magnesium-decorated Mg10C60 fullerenes, denoted as Mg−C60@MOF, places exposed metal sites with high heats of gas adsorption into intimate contact with large surface area MOF structures. Perhaps surprisingly, given the void space occupied by C60, this impregnation delivers remarkable gas uptake, according to our modeling, which predicts exceptional performance for the Mg−C60@MOF family of materials. These predictions include a volumetric methane uptake of 265 v/v, the highest reported value for any material, which significantly exceeds the U.S. Department of Energy target of 180 v/v. We also predict a very high hydrogen adsorption enthalpy of 11 kJ mol−1 with relatively little decr...

Journal ArticleDOI
TL;DR: In this article, a diblock copolymer based on regioregular poly(3-hexylthiophene) (P3HT) and fullerene was synthesized.
Abstract: A new, well-defined diblock copolymer (P3HT-b-C60) based on regioregular poly(3-hexylthiophene) (P3HT) and fullerene was synthesized. First, regioregular P3HT was synthesized through Grignard metathesis polymerization, and then methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) were copolymerized by using an end-functionalized P3HT as a macroinitiator for the atom transfer radical polymerization to yield a diblock copolymer (P3HT-b-P(MMA-r-HEMA)). A fullerene derivative functionalized with carboxylic acid, [6,6]-phenyl-C61-butyric acid (PCBA), was then chemically linked to the HEMA unit in the second block (P(MMA-r-HEMA)) to produce a diblock copolymer with the second block containing fullerenes. Annealing thin films of the copolymer revealed nanometer-scale phase separation, a more suitable morphology for enabling excitons generated in the P3HT domain to more efficiently reach the donor–acceptor interface, relative to simple blends of P3HT and C60. As a result, photoluminescence of the P3HT-b-C60diblock copolymer in the films showed a complete quenching of photoluminescence of P3HT, which is indicative of charge transfer between P3HT and fullerene.

Journal ArticleDOI
TL;DR: In this article, Nanocrystal/fullerene derivative inorganic-organic hybrid photodetectors exhibiting high detectivity for near-IR wavelengths and a linear power dependence are produced.
Abstract: Nanocrystal/fullerene derivative inorganic-organic hybrid photodetectors exhibiting high detectivity for near-IR wavelengths and a linear power dependence are produced. The ultrafast electron transfer from the PbS crystals to the fullerene opens a new route to obtaining efficient photodetectors that are appealing, cost-effective alternatives to the currently available technology.

Journal ArticleDOI
TL;DR: First principles calculations based on gradient corrected density functional theory and molecular dynamics simulations of Ca decorated fullerene yield some novel results that are ideal for Ca coated C60 to operate as a hydrogen storage material at near ambient temperatures with fast kinetics.
Abstract: First principles calculations based on gradient corrected density functional theory and molecular dynamics simulations of Ca decorated fullerene yield some novel results: (1) C60 fullerene decorated with 32 Ca atoms on each of its 20 hexagonal and 12 pentagonal faces is extremely stable. Unlike transition metal atoms that tend to cluster on a fullerene surface, Ca atoms remain isolated even at high temperatures. (2) C60Ca32 can absorb up to 62 H2 molecules in two layers. The first 30 H2 molecules dissociate and bind atomically on the 60 triangular faces of the fullerene with an average binding energy of 0.45 eV/H, while the remaining 32 H2 molecules bind on the second layer quasi-molecularly with an average binding energy of 0.11 eV/H2. These binding energies are ideal for Ca coated C60 to operate as a hydrogen storage material at near ambient temperatures with fast kinetics. (3) The gravimetric density of this hydrogen storage material can reach 6.2 wt %. Simple model calculations show that this density is the limiting value for higher fullerenes.

Journal Article
TL;DR: In this paper, first principles calculations based on gradient corrected density functional theory and molecular dynamics simulations of Ca decorated fullerene yield some novel results: (1) C60-Ca32 decorated with 32 Ca atoms on each of its 20 hexagonal and 12 pentagonal faces is extremely stable.
Abstract: First principles calculations based on gradient corrected density functional theory and molecular dynamics simulations of Ca decorated fullerene yield some novel results: (1) C60 fullerene decorated with 32 Ca atoms on each of its 20 hexagonal and 12 pentagonal faces is extremely stable. Unlike transition metal atoms that tend to cluster on a fullerene surface, Ca atoms remain isolated even at high temperatures. (2) C60Ca32 can absorb up to 62 H2 molecules in two layers. The first 30 H2 molecules dissociate and bind atomically on the 60 triangular faces of the fullerene with an average binding energy of 0.45 eV/H, while the remaining 32 H2 molecules bind on the second layer quasi-molecularly with an average binding energy of 0.11 eV/H2. These binding energies are ideal for Ca coated C60 to operate as a hydrogen storage material at near ambient temperatures with fast kinetics. (3) The gravimetric density of this hydrogen storage material can reach 6.2 wt %. Simple model calculations show that this density is the limiting value for higher fullerenes.

Journal ArticleDOI
TL;DR: An isomerically pure sample of Gd(3)N@C(78) has been extracted from the carbon soot formed in the electric-arc generation of fullerenes using hollow graphite rods packed with Gd (2)O(3), under an atmosphere of helium and dinitrogen.
Abstract: An isomerically pure sample of Gd3N@C78 has been extracted from the carbon soot formed in the electric-arc generation of fullerenes using hollow graphite rods packed with Gd2O3 and graphite powder under an atmosphere of helium and dinitrogen. Purification has been achieved by chromatographic methods and the product has been characterized by mass spectrometry, UV/vis absorption spectroscopy, and cyclic voltammetry. Although a number of endohedral fullerenes have been found to utilize the D3h(5)-C78 cage, comparison of the spectroscopic and electrochemical properties of the previously characterized Sc3N@D3h(5)-C78 with those of Gd3N@C78 reveals significant differences that indicate that these two endohedrals do not possess the same cage structure. A single crystal X-ray diffraction study indicates that the fullerene cage does not follow the isolated pentagon rule (IPR) but has two equivalent sites where two pentagons abut. The endohedral has been identified as Gd3N@C2(22010)-C78. Two of the gadolinium atoms...


Journal ArticleDOI
TL;DR: In this paper, the PhBT12/fullerene blend films were found to exhibit a crystalline nanoscale morphology with space-charge-limited mobility of holes as high as 4.0 × 10−4 cm2/Vs without thermal annealing, leading to moderately efficient devices.
Abstract: Bulk heterojunction solar cells based on blends of the new low band gap donor–acceptor copolymer, poly(N-(dodecyl)-3,6-bis(4-dodecyloxythiophen-2-yl)phthalimide) (PhBT12), and fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) were systematically investigated. The PhBT12/fullerene blend films were found to exhibit a crystalline nanoscale morphology with space-charge-limited mobility of holes as high as 4.0 × 10−4 cm2/Vs without thermal annealing, leading to moderately efficient devices. The performance of the solar cells varied significantly with PhBT12/fullerene composition, reaching a power conversion efficiency of 2.0% with a current density of 6.43 mA/cm2 and a fill factor of 0.55 for the 1:1 PhBT12/PC71BM blend devices. However, thermally annealed (120 °C) PhBT12/fullerene blend devices had negligible photovoltaic properties due to micrometer scale phase separation of the blends which is attributed to the long side chains. We expect that better photovoltaic performance can be achieved by modifying the polymer side chain length and the device processing as well. These results show that phthalimide-based donor–acceptor copolymer semiconductors, exemplified by PhBT12, are promising low band gap materials for developing efficient bulk heterojunction solar cells.

Journal ArticleDOI
TL;DR: In this paper, soluble, electroactive derivatives based upon dibenzo[b,def]chrysene are introduced, enabling the preparation of solution-processed solar cells based on small molecule blends.
Abstract: Soluble, electroactive derivatives based upon dibenzo[b,def]chrysene are introduced. These compounds do not chemically react with fullerenes, enabling the preparation of solution-processed solar cells based on small molecule blends. Device power conversion efficiencies of 2.25% are described and a correlation between processing conditions, film morphology, and device efficiencies is demonstrated.

Journal ArticleDOI
TL;DR: In this article, the influence of 1-(3-hexoxycarbonyl)propyl-1-phenyl-[6,6]-Lu3N@C81, Lu3N/C80-PCBH, a novel acceptor material, has on active layer morphology and the performance of organic photovoltaic (OPV) devices using this material is reported.
Abstract: Here the influence that 1-(3-hexoxycarbonyl)propyl-1-phenyl-[6,6]-Lu3N@C81, Lu3N@C80–PCBH, a novel acceptor material, has on active layer morphology and the performance of organic photovoltaic (OPV) devices using this material is reported. Polymer/fullerene blend films with poly(3-hexylthiophene), P3HT, donor material and Lu3N@C80–PCBH acceptor material are studied using absorption spectroscopy, grazing incident X-ray diffraction and photocurrent spectra of photovoltaic devices. Due to a smaller molecular orbital offset the OPV devices built with Lu3N@C80–PCBH display increased open circuit voltage over empty cage fullerene acceptors. The photovoltaic performance of these metallo endohedral fullerene blend films is found to be highly impacted by the fullerene loading. The results indicate that the optimized blend ratio in a P3HT matrix differs from a molecular equivalent of an optimized P3HT/[6,6]-phenyl-C61-butyric methyl ester, C60–PCBM, active layer, and this is related to the physical differences of the C80 fullerene. The influence that active layer annealing has on the OPV performance is further evaluated. Through properly matching the film processing and the donor/acceptor ratio, devices with power conversion efficiency greater than 4% are demonstrated.

Journal ArticleDOI
TL;DR: High-order harmonic generation from C60 by an intense femtosecond Ti:sapphire laser is demonstrated for the first time, indicating fullerenes as the source of high-order harmonics.
Abstract: We demonstrate, for the first time, high-order harmonic generation from C60 by an intense femtosecond Ti:sapphire laser. Laser-produced plasmas from C60-rich epoxy and C60 films were used as the nonlinear media. Harmonics up to the 19th order were observed. The harmonic yield from fullerene-rich plasma is about 25 times larger compared with those produced from a bulk carbon target. Structural studies of plasma debris confirm the presence and integrity of fullerenes within the plasma plume, indicating fullerenes as the source of high-order harmonics.

Journal ArticleDOI
14 Oct 2009-ACS Nano
TL;DR: Computer simulation of metal-catalyzed SWNT nucleation on metal catalyst particles uses nonequilibrium density functional tight-binding molecular dynamics simulations and reports nucleation of sp(2)-carbon cap structures on an iron particle consisting of 38 atoms.
Abstract: The atomic scale details of single-walled carbon nanotube (SWNT) nucleation on metal catalyst particles are elusive to experimental observations. Computer simulation of metal-catalyzed SWNT nucleation is a challenging topic but potentially of great importance to understand the factors affecting SWNT diameters, chirality, and growth efficiency. In this work, we use nonequilibrium density functional tight-binding molecular dynamics simulations and report nucleation of sp(2)-carbon cap structures on an iron particle consisting of 38 atoms. One C(2) molecule was placed every 1.0 ps around an Fe(38) cluster for 30 ps, after which a further 410 ps of annealing simulation without carbon supply was performed. We find that sp(2)-carbon network nucleation and annealing processes occur in three sequential and repetitive stages: (A) polyyne chains on the metal surface react with each other to evolve into a Y-shaped polyyne junction, which preferentially form a five-membered ring as a nucleus; (B) polyyne chains on the first five-membered ring form an additional fused five- or six-membered ring; and (C) pentagon-to-hexagon self-healing rearrangement takes place with the help of short-lived polyyne chains, stabilized by the mobile metal atoms. The observed nucleation process resembles the formation of a fullerene cage. However, the metal particle plays a key role in differentiating the nucleation process from fullerene cage formation, most importantly by keeping the growing cap structure from closing into a fullerene cage and by keeping the carbon edge "alive" for the addition of new carbon material.