Showing papers on "Fullerene published in 2018"

Nonfullerene Acceptor Molecules for Bulk Heterojunction Organic Solar Cells

Abstract: The bulk-heterojunction blend of an electron donor and an electron acceptor material is the key component in a solution-processed organic photovoltaic device. In the past decades, a p-type conjugated polymer and an n-type fullerene derivative have been the most commonly used electron donor and electron acceptor, respectively. While most advances of the device performance come from the design of new polymer donors, fullerene derivatives have almost been exclusively used as electron acceptors in organic photovoltaics. Recently, nonfullerene acceptor materials, particularly small molecules and oligomers, have emerged as a promising alternative to replace fullerene derivatives. Compared to fullerenes, these new acceptors are generally synthesized from diversified, low-cost routes based on building block materials with extraordinary chemical, thermal, and photostability. The facile functionalization of these molecules affords excellent tunability to their optoelectronic and electrochemical properties. Within t...

Charged Carbon Nanomaterials: Redox Chemistries of Fullerenes, Carbon Nanotubes, and Graphenes

Abstract: Since the discovery of buckminsterfullerene over 30 years ago, sp2-hybridised carbon nanomaterials (including fullerenes, carbon nanotubes, and graphene) have stimulated new science and technology across a huge range of fields. Despite the impressive intrinsic properties, challenges in processing and chemical modification continue to hinder applications. Charged carbon nanomaterials (CCNs), formed via the reduction or oxidation of these carbon nanomaterials, facilitate dissolution, purification, separation, chemical modification, and assembly. This approach provides a compelling alternative to traditional damaging and restrictive liquid phase exfoliation routes. The broad chemistry of CCNs not only provides a versatile and potent means to modify the properties of the parent nanomaterial but also raises interesting scientific issues. This review focuses on the fundamental structural forms: buckminsterfullerene, single-walled carbon nanotubes, and single-layer graphene, describing the generation of their respective charged nanocarbon species, their interactions with solvents, chemical reactivity, specific (opto)electronic properties, and emerging applications.

The role of fullerenes in the environmental stability of polymer:fullerene solar cells

Abstract: Environmental stability is a common challenge for the commercialisation of low cost, encapsulation-free organic opto-electronic devices. Understanding the role of materials degradation is the key to address this challenge, but most such studies have been limited to conjugated polymers. Here we quantitatively study the role of the common fullerene derivative PCBM in limiting the stability of benchmark organic solar cells, showing that a minor fraction (<1%) of photo-oxidised PCBM, induced by short exposure to either solar or ambient laboratory lighting conditions in air, consistent with typical processing and operating conditions, is sufficient to compromise device performance severely. We identify the effects of photo-oxidation of PCBM on its chemical structure, and connect this to specific changes in its electronic structure, which significantly alter the electron transport and recombination kinetics. The effect of photo-oxidation on device current–voltage characteristics, electron mobility and density of states could all be explained with the same model of photoinduced defects acting as trap states. Our results demonstrate that the photochemical instability of PCBM and chemically similar fullerenes remains a barrier for the commercialisation of organic opto-electronic devices.

Fullerenes as photosensitizers in photodynamic therapy: pros and cons.

Abstract: One class of carbon nanomaterials is the closed cages known as fullerenes. The first member to be discovered in 1985 was C60, called “buckminsterfullerene” as its cage structure resembled a geodesic dome. Due to their extended π-conjugation they absorb visible light, possess a high triplet yield and can generate reactive oxygen species upon illumination, suggesting a possible role of fullerenes in photodynamic therapy (PDT). Pristine C60 is highly hydrophobic and prone to aggregation, necessitating functionalization to provide aqueous solubility and biocompatibility. The most common functional groups attached are anionic (carboxylic or sulfonic acids) or cationic (various quaternary ammonium groups). Depending on the functionalization, these fullerenes can be designed to be taken up into cancer cells, or to bind to microbial cells (Gram-positive, Gram-negative bacteria, fungi). Fullerenes can be excited with a wide range of wavelengths, UVA, blue, green or white light. We have reported a series of functionalized fullerenes (C60, C70, C82) with attached polycationic chains and additional light-harvesting antennae that can be used in vitro and in animal models of localized infections. Advantages of fullerenes as photosensitizers are: (a) versatile functionalization; (b) light-harvesting antennae; (c) ability to undergo Type 1, 2, and 3 photochemistry; (d) electron transfer can lead to oxygen-independent photokilling; (e) antimicrobial activity can be potentiated by inorganic salts; (f) can self-assemble into supramolecular fullerosomes; (g) components of theranostic nanoparticles; (h) high resistance to photobleaching. Disadvantages include: (a) highly hydrophobic and prone to aggregation; (b) overall short wavelength absorption; (c) relatively high molecular weight; (d) paradoxically can be anti-oxidants; (e) lack of fluorescence emission for imaging.

Progress in fullerene-based hybrid perovskite solar cells

Abstract: In this review, we summarize recent advances that have resulted in fullerene-based high-efficiency perovskite solar cells (PSCs) by new processing methods of the perovskite films, by adding fullerenes as interfacial selective electron extraction layers and improving device stability or by incorporating fullerene derivatives to eliminate hysteretic behavior of both regular and inverted PSC structures. Finally, we outline some perspectives for further advancing PSCs for large-scale and commercial applications.

Evolution of glassy carbon under heat treatment: correlation structure–mechanical properties

Abstract: In order to accommodate an increasing demand for glassy carbon products with tailored characteristics, one has to understand the origin of their structure-related properties. In this work, through the use of high-resolution transmission electron microscopy, Raman spectroscopy, and electron energy loss spectroscopy it has been demonstrated that the structure of glassy carbon at different stages of the carbonization process resembles the curvature observed in fragments of nanotubes, fullerenes, or nanoonions. The measured nanoindentation hardness and reduced Young’s modulus change as a function of the pyrolysis temperature from the range of 600–2500 °C and reach maximum values for carbon pyrolyzed at around 1000 °C. Essentially, the highest values of the mechanical parameters for glassy carbon manufactured at that temperature can be related to the greatest amount of non-planar sp 2 -hybridized carbon atoms involved in the formation of curved graphene-like layers. Such complex labyrinth-like structure with sp 2 -type bonding would be rigid and hard to break that explains the glassy carbon high strength and hardness.

Closely packed, low reorganization energy π-extended postfullerene acceptors for efficient polymer solar cells

Abstract: New organic semiconductors are essential for developing inexpensive, high-efficiency, solution-processable polymer solar cells (PSCs). PSC photoactive layers are typically fabricated by film-casting a donor polymer and a fullerene acceptor blend, with ensuing solvent evaporation and phase separation creating discrete conduits for photogenerated holes and electrons. Until recently, n-type fullerene acceptors dominated the PSC literature; however, indacenodithienothiophene (IDTT)-based acceptors have recently enabled remarkable PSC performance metrics, for reasons that are not entirely obvious. We report two isomeric IDTT-based acceptors 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-benz-(5, 6)indanone))-5,5,11,11-tetrakis(4-nonylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]di-thiophene (ITN-C9) and 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-benz(6,7)indanone))-5,5,11,11-tetrakis(4-nonylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITzN-C9) that shed light on the exceptional IDTT properties vis-a-vis fullerenes. The neat acceptors and blends with fluoropolymer donor poly{[4,8-bis[5-(2- ethylhexyl)-4-fluoro-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene2,6-diyl]-alt-[2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]]} (PBDB-TF) are investigated by optical spectroscopy, cyclic voltammetry, thermogravimetric analysis, differential scanning calorimetry, single-crystal X-ray diffraction, photovoltaic response, space-charge-limited current transport, atomic force microscopy, grazing incidence wide-angle X-ray scattering, and density functional theory-level quantum chemical analysis. The data reveal that ITN-C9 and ITzN-C9 organize such that the lowest unoccupied molecular orbital-rich end groups have intermolecular π−π distances as close as 3.31(1) A, with electronic coupling integrals as large as 38 meV, and internal reorganization energies as small as 0.133 eV, comparable to or superior to those in fullerenes. ITN-C9 and ITzN-C9 have broad solar-relevant optical absorption, and, when blended with PBDB-TF, afford devices with power conversion efficiencies near 10%. Performance differences between ITN-C9 and ITzN-C9 are understandable in terms of molecular and electronic structure distinctions via the influences on molecular packing and orientation with respect to the electrode.

Fullerene‐Based Materials for Photovoltaic Applications: Toward Efficient, Hysteresis‐Free, and Stable Perovskite Solar Cells

Abstract: Perovskite solar cells are promising candidates for next-generation photovoltaics. Fullerenes and their derivatives can act as efficient electron transport layers, interfacial modification layers, ...

Carbyne: from the elusive allotrope to stable carbon atom wires

Abstract: Besides graphite and diamond, the solid allotropes of carbon in sp2 and sp3 hybridization, the possible existence of a third allotrope based on the sp-carbon linear chain, the carbyne, has stimulated researchers for a long time. The advent of fullerenes, nanotubes, and graphene has opened new opportunities and nurtured the interest in novel carbon allotropes, including linear structures. The efforts made in this direction produced a number of interesting sp-hybridized carbon molecules and nanostructures in the form of carbon-atom wires. Here we discuss some of the new perspectives opened by the recent advancements in the research on sp-carbon systems.

Azabuckybowl-Based Molecular Tweezers as C60 and C70 Receptors

Abstract: We designed and synthesized molecular tweezers consisting of nitrogen-embedded buckybowl subunits. The judicious choice of the covalent linkers modulated their binding strength with C60 or C70 in solution. Titration studies by optical and 1H NMR analyses revealed a 1:1 composition of the resulting complexes. X-ray diffraction analysis elucidated their solid-state structures, in which two azabuckybowl units surround one fullerene molecule. The large association constants stabilize the complexes toward redox reactions and the purification process on silica-gel column chromatography. The linker enabled tuning of the cavity size for binding of fullerenes, achieving complementary fullerene hosts for C60 and C70: the carbazole-bridged dimer preferentially associates with C70 over C60, while the phenanthrene-bridged dimer interacts with C60 more strongly than C70. Electrochemical analysis in combination with density functional theory calculations indicated the existence of intermolecular charge-transfer interact...

Adsorption and possible dissociation of glucose by the [BN fullerene-B 6 ] − magnetic nanocomposite. In silico studies

Abstract: The adsorption, activation and possible dissociation of the glucose molecule on the magnetic [BN fullerene-B6]− system is performed by means of density functional theory calculations. Three models of magnetic nanocomposites were inspected: i) pristine BN fullerene, BN fullerene functionalized with a magnetic B6 cluster which generates two structures: ii) pyramidal (P) and iii) triangular (T). Chemical interactions of glucose appear for all these cases; however, for the BNF:B6(T)—glucose system, the interaction generates an effect of dissociation on glucose, due to the magnetic effects, since it has high spin multiplicity. The latter nanocomposite shows electronic behavior like-conductor and like-semi-conductor for the P and T geometries, respectively. Intrinsic magnetism associated to values of 1.0 magneton bohr (µB) for the pyramidal and 5.0 µB for the triangular structure, high polarity, and low-chemical reactivity are found for these systems. These interesting properties make these functionalized fullerenes a good option for being used as nano-vehicles for drug delivery. These quantum descriptors remain invariant when the [BN]−fullerene and [BNF:B6 (P) or (T)]− nanocomposites are interacting with the glucose molecule. According to the determined adsorption energy, chemisorption regimes occur in both the phases: gas and aqueous medium.

U2@Ih(7)-C80: Crystallographic Characterization of a Long-Sought Dimetallic Actinide Endohedral Fullerene

Abstract: The nature of actinide–actinide bonds has attracted considerable attention for a long time, especially since recent theoretical studies suggest that triple and up to quintuple bonds should be possible, but little is known experimentally Actinide–actinide bonds inside fullerene cages have also been proposed, but their existence has been debated intensively by theoreticians Despite all the theoretical arguments, critical experimental data for a dimetallic actinide endohedral fullerene have never been obtained Herein, we report the synthesis and isolation of a dimetallic actinide endohedral metallofullerene (EMF), U2@C80 This compound was fully characterized by mass spectrometry, single crystal X-ray crystallography, UV–vis–NIR spectroscopy, Raman spectroscopy, cyclic voltammetry, and X-ray absorption spectroscopy (XAS) The single crystal X-ray crystallographic analysis unambiguously assigned the molecular structure to U2@Ih(7)-C80 In particular, the crystallographic data revealed that the U–U distance

Bonding inside and outside Fullerene Cages.

Abstract: ConspectusConcrete crystallographic results of endohedral metallofullerenes (EMFs) disclose that the bonding within the metallic clusters and the interactions between the metal ions and the cage carbon atoms, which are closely associated with the coordination ability of the metal ions, play essential roles in determining the stability, the molecular structure, and the chemical behavior of the hybrid EMF molecules, in addition to the previously recognized charge transfer from metal to cage. For the carbide cluster metallofullerenes, a “size effect” between the encapsulated metallic cluster and the fullerene cage has been suggested. Thus, through the geometric effect, a series of giant fullerenes (C90–C104) have been stabilized by encapsulating a large La2C2 cluster, which adopts different configurations in accordance with cage size and shape. Interestingly, the crystallographic analysis of La2C2@D5(450)-C100 has led to the direct observation of the axial compression of short carbon nanotubes caused by the ...

Anchoring Fullerene onto Perovskite Film via Grafting Pyridine toward Enhanced Electron Transport in High-Efficiency Solar Cells

Abstract: Fullerene derivatives have been popularly applied as electron transport layers (ETLs) of inverted (p–i–n) planar heterojunction perovskite solar cells (iPSCs) due to their strong electron-accepting abilities, and so far, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) has been the most commonly used ETL, which suffers, however, from high cost due to the complicated synthetic route. Herein, novel pyridine-functionalized fullerene derivatives (abbreviated as C60-Py) were synthesized facilely via a one-step 1,3-dipolar cycloaddition reaction and applied as ETLs superior to PCBM in iPSC devices. Three pyridine-functionalized fullerene derivatives with different alkyl groups, including methyl, n-butyl, and n-hexyl, grafted onto the pyrrolidine moiety (abbreviated as C60-MPy, C60-BPy, and C60-HPy, respectively) were synthesized. According to cyclic voltammogram study, the chain length of the N-alkyl group has negligible influence on the molecular energy level of C60-Py. However, the ETL performance of C60-Py ...

Centimetre-scale electron diffusion in photoactive organic heterostructures

Abstract: The unique properties of organic semiconductors, such as flexibility and lightness, are increasingly important for information displays, lighting and energy generation. But organics suffer from both static and dynamic disorder, and this can lead to variable-range carrier hopping, which results in notoriously poor electrical properties, with low electron and hole mobilities and correspondingly short charge-diffusion lengths of less than a micrometre. Here we demonstrate a photoactive (light-responsive) organic heterostructure comprising a thin fullerene channel sandwiched between an electron-blocking layer and a blended donor:C70 fullerene heterojunction that generates charges by dissociating excitons. Centimetre-scale diffusion of electrons is observed in the fullerene channel, and this can be fitted with a simple electron diffusion model. Our experiments enable the direct measurement of charge diffusivity in organic semiconductors, which is as high as 0.83 ± 0.07 square centimetres per second in a C60 channel at room temperature. The high diffusivity of the fullerene combined with the extraordinarily long charge-recombination time yields diffusion lengths of more than 3.5 centimetres, orders of magnitude larger than expected for an organic system.

Overcoming Space-Charge Effect for Efficient Thick-Film Non-Fullerene Organic Solar Cells

Abstract: DOI: 10.1002/aenm.201801609 non-fullerene acceptors (NFAs), which exhibit large tunability in energy levels and absorption spectra, providing more opportunities for the achievement of high-performance devices.[1–3] Benefiting from novel acceptor or donor material design[4–8] and device engineering,[9–11] the power conversion efficiencies (PCEs) of non-fullerene OSCs were dramatically increased from 6% to 14% in just a few years.[8,12] These novel NFAs are small molecules or polymers based on fused rings, such as perylene diimide,[13–16] naphthalene diimide,[17,18] and indacenodithiophene (IDT).[5,19–21] Among them, IDT-based small molecules are the most widely studied NFAs and have the best potential to achieve high-performance devices.[5,22–29] However, most studies on the NFA-based OSCs were focused on boosting the PCE; fewer concentrated on issues related to future industrialization, including operation stability[30] and technologies for achieving efficient thick-film devices that are required for high speed, large-area manufacturing process.[31] It is well known that most IDT-based NFAs exhibit an electron mobility of about 10−4–10−5 cm2 V−1 s−1, which is lower than that of fullerene acceptors (≈10−3 cm2 V−1 s−1); this unbalance in charge transport properties limits the optimal active layer thickness of these devices to about 100 nm. Only a few studies reported relatively efficient thick-film non-fullerene OSCs based on exceptional acceptors with improved mobility,[20,32–34] and there remains a lack of more in-depth studies and strategies to achieve efficient thick-film non-fullerene OSCs. In this work, we demonstrate an effective strategy to realize efficient thick-film non-fullerene OSCs by overcoming the space-charge effects. Blends of a donor poly[(5,6-difluoro2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′′′-di(2-octyldodecyl)2,2′;5′,2′′;5′′,2′′′-quaterthiophen-5,5′′′-diyl)] (PffBT4T-2OD)[35] and a non-fullerene small molecule acceptor EH-IDTBR (consists of electron-rich indaceno[1,2-b:5,6-b′]dithiophene as the central unit and an electron-deficient 5,6-benzo[c][1,2,5] thiadiazole unit flanked with rhodanine as the peri pheral group)[21] are chosen as the active layer because of their excellent device stability and these may be good candidates for commercial OSC applications.[36] Furthermore, PffBT4T2OD can offer highly efficient thick-film OSCs with blends of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which Organic solar cells (OSCs) containing non-fullerene acceptors have realized high power conversion efficiency (PCE) up to 14%. However, most of these high-performance non-fullerene OSCs have been reported with optimal active layer thickness of about 100 nm, mainly due to the low electron mobility (≈10−4–10−5 cm2 V−1 s−1) of non-fullerene acceptors, which are not suitable for roll-to-roll large-scale processing. In this work, an efficient non-fullerene OSC based on poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′′′di(2-octyldodecyl)-2,2′;5′,2′′;5′′,2′′′-quaterthiophen-5,5′′′-diyl)] (PffBT4T-2OD): EH-IDTBR (consists of electron-rich indaceno[1,2-b:5,6-b′]dithiophene as the central unit and an electron-deficient 5,6-benzo[c][1,2,5]thiadiazole unit flanked with rhodanine as the peripheral group) with thickness-independent PCE (maintaining a PCE of 9.1% with an active layer thickness of 300 nm) is presented by optimizing device architectures to overcome the space-charge effects. Optical modeling reveals that most of the incident light is absorbed near the transparent electrode side in thick-film devices. The transport distance of electrons with lower mobility will therefore be shortened when using inverted device architecture, in which most of the excitons are generated close to the cathode side and therefore substantially reduces the accumulation of electrons in the device. As a result, an efficient thick-film non-fullerene OSC is realized. These results provide important guidelines for the development of more efficient thick-film non-fullerene OSCs.

A diuranium carbide cluster stabilized inside a C80 fullerene cage.

Abstract: Unsupported non-bridged uranium-carbon double bonds have long been sought after in actinide chemistry as fundamental synthetic targets in the study of actinide-ligand multiple bonding. Here we report that, utilizing Ih(7)-C80 fullerenes as nanocontainers, a diuranium carbide cluster, U=C=U, has been encapsulated and stabilized in the form of UCU@Ih(7)-C80. This endohedral fullerene was prepared utilizing the Kratschmer-Huffman arc discharge method, and was then co-crystallized with nickel(II) octaethylporphyrin (NiII-OEP) to produce UCU@Ih(7)-C80·[NiII-OEP] as single crystals. X-ray diffraction analysis reveals a cage-stabilized, carbide-bridged, bent UCU cluster with unexpectedly short uranium-carbon distances (2.03 A) indicative of covalent U=C double-bond character. The quantum-chemical results suggest that both U atoms in the UCU unit have formal oxidation state of +5. The structural features of UCU@Ih(7)-C80 and the covalent nature of the U(f1)=C double bonds were further affirmed through various spectroscopic and theoretical analyses.

Achieving High Efficiency in Solution-Processed Perovskite Solar Cells Using C60/C70 Mixed Fullerenes

Abstract: Fullerenes have attracted considerable interest as an electron-transporting layer in perovskite solar cells. Fullerene-based perovskite solar cells produce no hysteresis and do not require high-temperature annealing. However, high power conversion efficiency has been only achieved when the fullerene layer is thermally evaporated, which is an expensive process. In this work, the limitations of a solution-processed fullerene layer have been identified as high crystallinity and the presence of remnant solvents, in contrast to a thermally deposited C60 film, which has low crystallinity and no remaining solvents. As a solution to these problems, a mixed C60 and C70 solution-processed film, which exhibits low crystallinity, is proposed as an electron-transporting layer. The mixed-fullerene-based devices produce power conversion efficiencies as high as that of the thermally evaporated C60-based device (16.7%) owing to improved fill factor and open-circuit voltage. In addition, by vacuum-drying the mixed fulleren...

N-Type Doping of Fullerenes for Planar Perovskite Solar Cells

Abstract: Modification of TiO2 by using fullerenes is an efficient strategy to further improve the device efficiency and enhance the cell stability of perovskite solar cells (PSCs). However, the intrinsic issues of low electron mobility and electrical conductivity of fullerene materials may restrict their potential application in PSCs. Here, we demonstrated an n-doped electron-transporting layer by doping bis(1-[3-(methoxycarbonyl)propyl]-1-phenyl)-[6,6]C62 (bis-PCBM) with decamethylcobaltocene (DMC) to fabricate n–i–p structure PSCs. We successfully realized an n-type doping of bis-PCBM via a solution-processed doping process. DMC doping played a series of roles in adjusting the energy levels, improving the electron mobility and enhancing the film conductivity of bis-PCBM. A bis-PCBM:DMC composite film could act as an underlay for the deposition and growth of a subsequent perovskite layer owing to its smooth morphology. In addition, the bis-PCBM:DMC composite film also presented good solvent resistance, which coul...

Graphene and related 2D materials: An overview of the Raman studies

Abstract: A After a brief overview of the discovery and the Raman study of new forms of carbons (intercalated graphite, carbon fiber, fullerenes, carbon nanotubes), the invaluable contribution of late Professor M. Dresselhaus is noted and the 10 reviews and 10 contributions collected to present a picture of the present Raman investigations of graphene and related 2D materials (such as black phosphorus, MoS2) are presented. Methods for numbering the graphene layers, the effects of external perturbations (temperature, pressure, doping and magnetic field) on the phonons of graphene, characterization of the chemical and structural properties of graphene at the nanoscale level by tip-enhanced Raman spectroscopy (TERS), surface enhanced Raman spectroscopy (SERS) and hyperspectral imaging, and applications combining graphene and Raman spectroscopy are addressed.