Ian Tevis

One of the challenges facing bulk heterojunction organic solar cells is obtaining organized films during the phase separation of intimately mixed donor and acceptor components. We report here on the use of hairpin-shaped sexithiophene molecules to generate by self-assembly grooved nanowires as the donor component in bulk heterojunction solar cells. Photovoltaic devices were fabricated via spin-casting to produce by solvent evaporation a percolating network of self-assembled nanowires and… Show more

One of the challenges facing bulk heterojunction organic solar cells is obtaining organized films during the phase separation of intimately mixed donor and acceptor components. We report here on the use of hairpin-shaped sexithiophene molecules to generate by self-assembly grooved nanowires as the donor component in bulk heterojunction solar cells. Photovoltaic devices were fabricated via spin-casting to produce by solvent evaporation a percolating network of self-assembled nanowires and fullerene acceptors. Thermal annealing was found to increase power conversion efficiencies by promoting domain growth while still maintaining this percolating network of nanostructures. The benefits of self-assembly and grooved nanowires were examined by building devices from a soluble sexithiophene derivative that does not form one-dimensional structures. In these systems, excessive phase separation caused by thermal annealing leads to the formation of defects and lower device efficiencies. We propose that the unique hairpin shape of the self-assembling molecules allows the nanowires as they form to interact well with the fullerenes in receptor–ligand type configurations at the heterojunction of the two domains, thus enhancing device efficiencies by 23%. Show less

One of the challenges in organic systems with semiconducting function is the achievement of molecular orientation over large scales. We report here on the use of self-assembly kinetics to control long-range orientation of a quarterthiophene derivative designed to combine intermolecular π–π stacking and hydrogen bonding among amide groups. Assembly of these molecules in the solution phase is prevented by the hydrogen-bond-accepting solvent tetrahydrofuran, whereas formation of H-aggregates is… Show more

One of the challenges in organic systems with semiconducting function is the achievement of molecular orientation over large scales. We report here on the use of self-assembly kinetics to control long-range orientation of a quarterthiophene derivative designed to combine intermolecular π–π stacking and hydrogen bonding among amide groups. Assembly of these molecules in the solution phase is prevented by the hydrogen-bond-accepting solvent tetrahydrofuran, whereas formation of H-aggregates is facilitated in toluene. Rapid evaporation of solvent in a solution of the quarterthiophene in a 2:1:1 mixture of 1,4-dioxane/tetrahydrofuran/toluene leads to self-assembly of kinetically trapped mats of bundled fibers. In great contrast, slow drying in a toluene atmosphere leads to the homogeneous nucleation and growth of ordered structures shaped as rhombohedra or hexagonal prisms depending on concentration. Furthermore, exceedingly slow delivery of toluene from a high molecular weight polymer solution into the system through a porous aluminum oxide membrane results in the growth of highly oriented hexagonal prisms perpendicular to the interface. The amide groups of the compound likely adsorb onto the polar aluminum oxide surface and direct the self-assembly pathway toward heterogeneous nucleation and growth to form hexagonal prisms. We propose that the oriented prismatic polymorph results from the synergy of surface interactions rooted in hydrogen bonding on the solid membrane and the slow kinetics of self-assembly. These observations demonstrate how self-assembly conditions can be used to guide the supramolecular energy landscape to generate vastly different structures. These fundamental principles allowed us to grow oriented prismatic assemblies on transparent indium-doped tin oxide electrodes, which are of interest in organic electronics. Show less

The cyclic carbonate moiety finds many industrial applications because of its unique chemistry and properties. Phosgene, a highly toxic and corrosive reagent, has been utilized in the past to prepare low yields of fatty ester compounds (1) that contain a five-membered cyclic carbonate group. Herein, we show (CH3)4N+−HCO3, tetramethylammonium hydrogen carbonate (TMAHC), to react efficiently with methyl or 2-ethylhexyl 9(10)chloro-10(9)-hydroxyoctadecanoate at 50–55 °C to give methyl or… Show more

The cyclic carbonate moiety finds many industrial applications because of its unique chemistry and properties. Phosgene, a highly toxic and corrosive reagent, has been utilized in the past to prepare low yields of fatty ester compounds (1) that contain a five-membered cyclic carbonate group. Herein, we show (CH3)4N+−HCO3, tetramethylammonium hydrogen carbonate (TMAHC), to react efficiently with methyl or 2-ethylhexyl 9(10)chloro-10(9)-hydroxyoctadecanoate at 50–55 °C to give methyl or 2-ethylhexyl 8-(2-oxo-5-octyl-1,3-dioxolan-4-yl)octanoate, 1a and 1b, respectively. These fatty acid ester carbonates were isolated in good yields ranging from 84% to 91% after purification by vacuum distillation. The purified fatty ester carbonate compounds were characterized by 1H and 13C nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and gas chromatography-mass spectrometry using electron impact ionization and positive chemical ionization techniques. This work demonstrates that the five-membered cyclic carbonate ring can be effectively introduced onto the alkyl chains of fatty acid esters using fatty ester chlorohydrins and (CH3)4N+−HCO3 chemistry. The well-known lubricating and polymeric properties of the carbonate moiety make these interesting cyclic oleochemical carbonates potential candidates for industrial lubricant, plasticizer, or polymer applications. Show less