Epitaxy-Assisted Creation of PCBM Nanocrystals and Its Application in Constructing Optimized Morphology for Bulk-Heterojunction Polymer Solar Cells

PCBM (a C-60 derivative) is so far the most successful electron acceptor for bulk-heterojunction polymer photovoltaic (PV) cells. Here we present a novel method epitaxy-assisted creation of PCBM nanocrystals and their homogeneous distribution in the matrix using freshly cleaved mica sheet as the substrate. The highly matched epitaxy relationship between the unit cell of PCBM crystal and crystallographic (001) surface of mica induces abundant PCBM nuclei, which subsequently develop into nanoscale crystals with homogeneous dispersion in the composite film.

Weak epitaxy growth and phase behavior of planar phthalocyanines on p-sexiphenyl monolayer film

We systematically investigated the weak epitaxy growth (WEG) behavior of a series of planar phthalocyanine compounds (MPc), i.e., metal-free phthalocyanine (H2PC), nickel phthalocyanine (NiPc), copper phthalocyanine (CuPc), zinc phthalocyanine (ZnPc), iron phthalocyanine (FePc); cobalt phthalocyanine (CoPc), grown on a p-sexiphenyl (p-6P) monolayer film by selected area electron diffraction (SAED) and atomic force microscopy (AFM). Two types of epitaxial relations, named as incommensurate epitaxy and commensurate epitaxy, were identified between phthalocyanine compounds and the substrate of the p-6P film.

Weak epitaxy growth of metal-free phthalocyanine on p-sexiphenyl monolayer and double-layer films

Weak epitaxy growth (WEG) can afford high-mobility thin films of disk-like organic semiconductor of which mobility is up to the level of the corresponding single crystals. We investigated the WEG behavior and mechanism of planar phthalocyanine in the model system of metal-free phthalocyanine (H2Pc) grown on p-sexiphenyl (p-6P) ultrathin films (monolayers and double layers). Highly oriented H2Pc films with molecules standing up exhibited two kinds of different in-plane orientations, i.e., three sets of in-plane orientations and only one set of in-plane orientation, on p-6P monolayer and double-layer films, respectively.

Weak epitaxy growth of organic semiconductor thin films

The fabrication of organic semiconductor thin films is extremely important in organic electronic devices. This tutorial review-which should particularly appeal to chemists and physicists interested in organic thin-film growth, organic electronic devices and organic semiconductor materials-summarizes the method of weak epitaxy growth (WEG) and its application in the fabrication of high quality organic semiconductor thin films.

Weak Epitaxy Growth of Copper Hexadecafluorophthalocyanine (F16CuPc) on p-Sexiphenyl Monolayer Film

Weak epitaxy growth (WEG) behavior and mechanism of copper hexadecafluorophthalocyanine (F16CuPc) on p-sexiphenyl (p-6P) monolayer film were investigated by atomic force microscopy (AFM), selected area electron diffraction (SEAD), and wide-angle X-ray diffraction (WAXD). High-quality F16CuPc films with high order, large size, and molecular-level smoothness were obtained successfully by WEG method. It was identified that there exists incommensurate epitaxial relation between highly oriented F16CuPc and p-6P films. The geometrical channels of p-6P monolayer surface induce the nucleation and growth of F16CuPc molecules.

Individual dispersion of synthetic imogolite nanotubes via droplet evaporation

Morphology of synthetic imogolite nanotubes formed in droplet evaporation was investigated by transmission electron microscopy and electron diffraction. The nanotubes form a dense entangled network at higher concentrations, while at lower concentrations the nanotubes are liable to form oriented bundles. Under enthanol atmosphere, individual dispersion of nanotubes was observed for the first time, which reveals the length polydispersity of synthetic imogolite nanotubes.

Weak epitaxy growth affording high-mobility thin films of disk-like organic semiconductors

Thin films of phthalocyanine compounds show weak epitaxial growth on a monodomain film of a rod-like molecule (see figure). The resulting organic electronic devices exhibit high charge carrier mobilities close to those of the single-crystal devices.

The influencing factors on the macroporous formation in polymer films by water droplet templating

Regular micrometer-size porous polystyrene film is prepared by water droplet templating, i.e. breath figures are stabilized by the polymer in solution and thermocapillary flow arranges them into ordered packing. The influences of polystyrene molecular weight, solvent properties, and the relative humidity of atmosphere on the pattern formation and hole sizes are investigated. Two different kinds of hole packing fashion are also observed and their formation mechanisms are discussed.

Ordered droplet formation by thin polymer film dewetting on a stripe-patterned substrate

The dewetting process of thin polystyrene (PS) film on flat and stripe-patterned substrates is presented. Different dewetting processes were observed when the thin PS films annealed at above the glass transition temperature on these different kinds of substrates. The final dewetting on the flat substrate led to formation of polygonal liquid droplets, while on the stripe-patterned substrate, the droplets were observed to align at the centers of the stripes. A possible explanation for the dewetting process on the stripe-patterned substrate is proposed.

A novel epitaxy of isotactic polypropylene (alpha phase) on PTFE and organic substrates

Isotactic polypropylene in its a modification (alpha iPP) crystallises epitaxially on polytetrafluoroethylene (PTFE) and several hemiacids or salts of substituted benzoic acids via a novel contact plane, namely (110): so far, the only known contact plane involved in alpha iPP homo- and hetero-epitaxies was (010). In spite of its complicated architecture (alternation of antichiral helices with different azimuthal settings), the (110)(alpha iPP) contact plane displays well defined, if not prominent, rows of methyl side chains parallel to the crystallographic (112) direction (at 57 degrees to the c-axis) and approximate to 5.5 Angstrom apart. The matching contact planes of the substrates display linear gratings made of rows of e.g. chlorine atoms or PTFE chains with similar approximate to 5.5 Angstrom inter-row or interchain distances. Various morphologies are observed in iPP thin films crystallised at different cooling rates in the presence of PTFE; they can be analysed in terms of a succession and interplay of successive epitaxies: initial alpha iPP/PTFE heteroepitaxy, followed by alpha iPP/alpha iPP and gamma iPP/alpha iPP homoepitaxies. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.

Study on the interface structure: Diamond thin film epitaxy on (001) silicon substrate

An interesting interface structure between diamond film and silicon substrate has been observed. That is, according to the deformation of the diamond film crystal sturcture, a strictly 3:2 matching of the two lattices across the interface is obtained. This result clearly indicates that misfit dislocations at the interface and "epitaxial tilting" are not the only two ways to overcome the 1.5% residual misfit.

Critical crystallization temperature for the occurrence of epitaxy between high-density polyethylene and isotactic polypropylene

The crystallization behavior of high-density polyethylene (HDPE) on highly oriented isotactic polypropylene (iPP) at elevated temperatures (e.g., from 125 to 128 degrees C), was studied using transmission electron microscopy and electron diffraction. The results show that epitaxial crystallization of HDPE on the highly oriented iPP substrates occurs only in a thin layer which is in direct contact with the iPP substrate, when the HDPE is crystallized from the melt on the oriented iPP substrates at 125 degrees C. The critical layer thickness of the epitaxially crystallized HDPE is not more than 30 nm when the HDPE is isothermally crystallized on the oriented iPP substrates at 125 degrees C. When the crystallization temperature is above 125 degrees C, the HDPE crystallizes in the form of crystalline aggregates and a few individual crystalline lamellae. But both the crystalline aggregates and the individual crystalline lamellae have no epitaxial orientation relationship with the iPP substrate. This means that there exists a critical crystallization temperature for the occurrence of epitaxial crystallization of HDPE on the melt-drawn oriented iPP substrates (i.e., 125 degrees C). (C) 1997 John Wiley & Sons, Inc.