The importance of p-n junction interfaces for efficient small molecule-based organic solar cells.

The efficiency of small-molecule solar cells critically depends on the match of the junction of the donor and acceptor semiconductors used in these devices to create charged carriers and on the mobility of individual components to transport holes and electrons. In the present study, a 2% efficient bilayer organic solar cell consisting of a p-type semiconductor, pentacene, and an n-type semiconductor, N,N'-diheptyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C(7)), is fabricated. The morphology of PTCDI-C(7) interestingly follows pentacene due to the matched surface energy of these two active layers and the easily deposited PTCDI-C(7) monomers on an inclined plane of the pentacene grains. This condition results in the low trap states in the PTCDI-C(7) film and at the pentacene/PTCDI-C(7) interface for the enhancement of exciton dissociation and carrier transport compared with the photoactive layer comprised of pentacene and N,N-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C(13)). The detailed exciton and carrier transport mechanisms are investigated using time-resolved photoluminescence and X-ray diffraction spectroscopy.

Electron transport properties in fluorinated copper-phthalocyanine films: importance of vibrational reorganization energy and molecular microstructure.

Electron transport (ET) properties of a series of fluorinated copper-phthalocyanine (F(16)CuPc) thin films, which were deposited at different substrate temperatures (T(sub)) ranging from 30 to 150 degrees C, have been investigated by quantum mechanical calculations of the reorganization energy (lambda(reorg)), X-ray diffraction (XRD), atomic force microscopy (AFM), and microRaman spectroscopy. Density functional theory calculations were used to predict the vibrational frequencies, normal mode displacement vectors, and electron-vibrational lambda(reorg) for the F(16)CuPc molecule. The electron mobilities (mu(e)) of F(16)CuPc thin films are strongly dependent on the T(sub), and the value of mu(e) increases with increasing T(sub) from 30 to 120 degrees C, at which point it reaches its maximum value. The importance of electron-vibrational coupling and molecular microstructures for ET properties in F(16)CuPc thin films are discussed on the basis of theoretical vibrational lambda(reorg) calculations and experimental observations of resonance Raman spectra. We observed a good correlation between mu(e) and the full-width-at-half-maximum of the vibrational bands, which greatly contributed to lambda(reorg) and/or which reflects the molecular microstructural quality of the active channel. In contrast, the crystal size analysis by XRD and surface grain morphology by AFM did not reveal a clear correlation with the ET behaviours for these different F(16)CuPc thin films. Therefore, we suggest that for organic films with weak intermolecular interactions, such as F(16)CuPc, optimized microscopic molecular-scale parameters are highly important for efficient long-range charge transport in the macroscopic devices.

Chelating agent-assisted heat treatment of a carbon-supported iron oxide nanoparticle catalyst for PEMFC.

Iron complexes were supported on commercial carbon black and heat treated to create FeO(x)/C catalysts that showed a larger normalized current density and normalized power density than commercial Pt/C catalysts; the coordination number of the iron complexes used affected the formation of the active site for oxygen reduction in PEMFC.

Investigation of electro-oxidation of methanol and benzyl alcohol at boron-doped diamond electrode: evidence for the mechanism for fouling film formation.

Boron-doped diamond (BDD) and glassy carbon (GC) electrodes are compared for electrochemical oxidation of methanol and benzyl alcohol. Cyclic voltammograms reveal that BDD electrode produces good oxidation signals for both methanol and benzyl alcohol, while GC produces no significant oxidation signal for either methanol or benzyl alcohol. Amperometric measurement of oxidation of methanol and benzyl alcohol on BDD shows development of a fouling film for benzyl alcohol but not for methanol. Prolonged (24 h) polarization of the BDD electrode at +2.0 V in benzyl alcohol generated enough fouling film for investigation by AFM, SEM, Raman, and FTIR techniques. AFM and SEM microscopy images confirm a fouling film confined to the low-lying regions of the polycrystallite BDD surface, indicating that the active sites of benzyl alcohol oxidation are located within these low-lying regions. The fouling material generated in the process of benzyl alcohol oxidation was identified from Raman and FTIR spectroscopy as polyester. Experiments confirm the fouling film can be removed and the electrode surface reactivated by brief polarization at +3.0 V. Amperometric results of concentration dependence confirm the BDD electrode is well suited for quantitative analysis applications of methanol and benzyl alcohol, with recognizable oxidation currents at micromolar concentration levels.

The effects of substitution on tetrakis(substituted imidazole)copper(II) trifluoromethanesulfonates.

The organic ligands 4-methyl-1H-imidazole and 2-ethyl-4-methyl-1H-imidazole react with Cu(CF(3)SO(3))(2).6H(2)O to give tetrakis(5-methyl-1H-imidazole-kappaN(3))copper(II) bis(trifluoromethanesulfonate), [Cu(C(4)H(6)N(2))(4)](CF(3)SO(3))(2), and aquatetrakis(2-ethyl-5-methyl-1H-imidazole-kappaN(3))copper(II) bis(tri fluoromethanesulfonate), [Cu(C(6)H(10)N(2))(4)(H(2)O)](CF(3)SO(3))(2). In the former, the Cu atom has an elongated octahedral coordination environment, with four imidazole rings in equatorial positions and two trifluoromethanesulfonate ions in axial positions. This conformation is similar to those in the analogous complexes tetrakis(imidazole)copper(II) trifluoromethanesulfonate and tetrakis(2-methyl-1H-imidazole)copper(II) trifluoromethanesulfonate. In the second of the title compounds, the ethyl groups block the central Cu atom, and a square-pyramidal coordination environment is formed around the Cu atom, with the substituted imidazole rings in the basal positions and a water molecule in the axial position.