Yutaka Matsuo

Columnar Structure in Bulk Heterojunction in Solution-Processable Three-Layered p-i-n Organic Photovoltaic Devices Using Tetrabenzoporphyrin Precursor and Silylmethyl[60]fullerene

A new solution-processable fabrication protocol using a soluble tetrabenzoporphyrin (BP) precursor and bis(dimethylphenylsilylmethyl)[60]fullerene (SIMEF) created three-layered p-i-n photovoltaic devices, in which the i-layer possesses a well-defined bulk heterojunction structure in which columnar BP crystals grow vertically from the bottom p-layer. The device showed a power conversion efficiency of 5.2% (V(OC) = 0.75 V; J(SC) = 10.5 mA/cm(2); FF = 0.65).

Direct and Dry Deposited Single-Walled Carbon Nanotube Films Doped with MoOx as Electron-Blocking Transparent Electrodes for Flexible Organic Solar Cells

UNLABELLED Organic solar cells have been regarded as a promising electrical energy source. Transparent and conductive carbon nanotube film offers an alternative to commonly used ITO in photovoltaics with superior flexibility. This communication reports carbon nanotube-based indium-free organic solar cells and their flexible application. Direct and dry deposited carbon nanotube film doped with MoO(x) functions as an electron-blocking transparent electrode, and its performance is enhanced further by overcoating with PEDOT PSS. The single-walled carbon nanotube organic solar cell in this work shows a power conversion efficiency of 6.04%. This value is 83% of the leading ITO-based device performance (7.48%). Flexible application shows 3.91% efficiency and is capable of withstanding a severe cyclic flex test.

Molecular photoelectric switch using a mixed SAM of organic [60]fullerene and [70]fullerene doped with a single iron atom.

We describe a photoswitch fabricated on indium tin oxide (ITO) as a self-assembled monolayer (SAM) of two fullerene molecules, a purely organic [60]fullerene that generates an anodic current and a [70]fullerene doped with a single iron atom. This device generates a bidirectional photocurrent upon irradiation at 340 and 490 nm. The new [70]fullerene iron complex bearing three rigid carboxylic acid legs, Fe[C(70)(C(6)H(4)C(6)H(4)COOH)(3)]Cp, generates only a cathodic current upon photoexcitation between 350 and 700 nm, whereas the organic [60]fullerene absorbs at wavelengths shorter than 500 nm. The quantum efficiency of the photocurrent generation by the mixed SAM is comparable to that of a single-component SAM, indicating that the individual diode molecules on ITO generate photocurrents independently with little cross talk.

Kinetic Study of the Diels–Alder Reaction of Li+@C60 with Cyclohexadiene: Greatly Increased Reaction Rate by Encapsulated Li+

We studied the kinetics of the Diels-Alder reaction of Li(+)-encapsulated [60]fullerene with 1,3-cyclohexadiene and characterized the obtained product, [Li(+)@C60(C6H8)](PF6(-)). Compared with empty C60, Li(+)@C60 reacted 2400-fold faster at 303 K, a rate enhancement that corresponds to lowering the activation energy by 24.2 kJ mol(-1). The enhanced Diels-Alder reaction rate was well explained by DFT calculation at the M06-2X/6-31G(d) level of theory considering the reactant complex with dispersion corrections. The calculated activation energies for empty C60 and Li(+)@C60 (65.2 and 43.6 kJ mol(-1), respectively) agreed fairly well with the experimentally obtained values (67.4 and 44.0 kJ mol(-1), respectively). According to the calculation, the lowering of the transition state energy by Li(+) encapsulation was associated with stabilization of the reactant complex (by 14.1 kJ mol(-1)) and the [4 + 2] product (by 5.9 kJ mol(-1)) through favorable frontier molecular orbital interactions. The encapsulated Li(+) ion catalyzed the Diels-Alder reaction by lowering the LUMO of Li(+)@C60. This is the first detailed report on the kinetics of a Diels-Alder reaction catalyzed by an encapsulated Lewis acid catalyst rather than one coordinated to a heteroatom in the dienophile.

Metal-electrode-free Window-like Organic Solar Cells with p-Doped Carbon Nanotube Thin-film Electrodes.

Organic solar cells are flexible and inexpensive, and expected to have a wide range of applications. Many transparent organic solar cells have been reported and their success hinges on full transparency and high power conversion efficiency. Recently, carbon nanotubes and graphene, which meet these criteria, have been used in transparent conductive electrodes. However, their use in top electrodes has been limited by mechanical difficulties in fabrication and doping. Here, expensive metal top electrodes were replaced with high-performance, easy-to-transfer, aerosol-synthesized carbon nanotubes to produce transparent organic solar cells. The carbon nanotubes were p-doped by two new methods: HNO3 doping via ‘sandwich transfer’, and MoOx thermal doping via ‘bridge transfer’. Although both of the doping methods improved the performance of the carbon nanotubes and the photovoltaic performance of devices, sandwich transfer, which gave a 4.1% power conversion efficiency, was slightly more effective than bridge transfer, which produced a power conversion efficiency of 3.4%. Applying a thinner carbon nanotube film with 90% transparency decreased the efficiency to 3.7%, which was still high. Overall, the transparent solar cells had an efficiency of around 50% that of non-transparent metal-based solar cells (7.8%).

Selective Synthesis of Co8S15 Cluster in Bowl-Shaped Template of the Pentaaryl[60]fullerene Ligand

A cobalt-sulfur cluster Co8S15 with molecular formula of (C60Ar5)-Co8S15(n)Bu2-(C60Ar5) (Ar = 4-(t)BuC6H4) was selectively synthesized from a pentaaryl[60]fullerene cobalt trisulfide complex, (η(5)-C60Ar5)CoS3. The bowl-shaped steric templating fullerene ligand, as well as the metastable cobalt trisulfide moiety, played important roles in the exclusive cluster formation. X-ray crystallography, as well as electrochemical, time-resolved photophysical, and magnetic, measurements revealed a mixed-valence cluster with six cobalt(III) and two high-spin cobalt(II) centers showing reversible redox behavior and photoinduced charge separation.

Regioselective acylation and carboxylation of [60]fulleroindoline via electrochemical synthesis

A regioselective and highly efficient electrochemical method for direct acylation and carboxylation of a [60]fulleroindoline has been developed. By using inexpensive and readily available acyl chlorides and chloroformates, both keto and ester groups can be easily attached onto the fullerene skeleton to afford 1,2,3,16-functionalized [60]fullerene derivatives regioselectively. In addition, a plausible mechanism for the formation of fullerenyl ketones and esters is proposed, and their further transformations under basic and acidic conditions have been investigated.

History of Li@C 60

Whereas endohedral metallo[60]fullerenes with lanthanide and alkaline earth metals were formed by laser vaporization or arc discharge, endohedral alkali metal-containing [60]fullerenes were produced by colliding ion beams or plasma with C60. In experiment colliding a lithium ion beam with C60, a mass peak assignable to Li@C60 was detected. Potassium plasma was also used, and a peak assignable to K@C60 was detected by mass spectrometry. Campbell and co-workers developed ion implantation method based on repeated irradiation of C60 with a lithium ion beam with the aim of isolating Li@C60. After applying this method, Li@C60 was extracted from the deposited film, and a fraction containing predominantly Li@C60 was separated by HPLC. Some physical properties of Li@C60 were investigated. The measured second-harmonic generation response of Li@C60 in the film as well as the third-order susceptibility of Li@C60 suggested that Li in the C60 cage enhances its second hyperpolarizability. The resistivity of the Li@C60 film was measured as 1.5 kΩ cm, about four orders of magnitude smaller than that of C60 films (ca. 50 MΩ cm).

New Directions in Li@C60 Research: Physical Measurements

Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy of [Li+@C60]\({{\text{PF}}_{6}}^{-}\) and Li@C60 were performed to elucidate their electronic structures. UPS of Li@C60 showed characteristic peaks due to electron transfer from the inner Li to the C60 cage. Dielectric measurement for [Li+@C60]\({{\text{PF}}_{6}}^{-}\) at low temperature revealed a phase transition temperature T C at 24 K. Above T C, the Li+ ion was localized at two equivalent position, suggesting quantum tunneling motion between the positions. Below T C, these two sites became inequivalent, with occupancies of 76 and 24%, creating electric dipole moments that were canceled by the antiferroelectric configuration of the crystal. Far-IR absorption measurements of [Li+@C60]\({{\text{PF}}_{6}}^{-}\) showed terahertz (THz) absorption because of the motion of inner Li+. Not only a rotational band (ca. 1.2 THz) at high temperature but also absorption bands due to restriction of Li+ motion at low temperature (ca. 2.2 and 2.65 THz) were observed in the THz spectra. The Li atom inside the C60 cage in carbon nanotubes was observed by transmission electron microscopy with electron energy loss spectroscopy.

Introduction to Endohedral Fullerenes with the C60 Cage

This introductory chapter explains endohedral metallo[60]fullerenes that have the C60 cage. Immediately after discovery of C60, interaction between fullerenes and the La atom was first discussed in 1985. Encapsulation of La in the fullerene cages was then demonstrated in 1991. Attempted extraction of La@C60 with hot toluene failed, whereas La@C82 was unexpectedly extracted. Subsequently, successful extraction of Ca@C60 was reported, and its molecular ion peak was observed in the mass spectrum of the extract. An improved extraction method using pyridine was developed, and various endohedral metallo[60]fullerenes were reported with the inner metals, such as Ba, Sr, Y, La, Ce, Pr, Nd, Gd, Er, Eu, and Dy atoms. However, little research has investigated the further chemical characterization and physical properties of these compounds. This is mainly because of the charge transfer interaction between the endohedral metallo[60]fullerenes and the specific solvent molecules such as pyridine. Satisfactorily, full chemical characterization of an endohedral metallo[60]fullerene was accomplished with lithium-containing [60]fullerene.