The surface composition of poly(3-hexylthiophene-2,5-diyl) and fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM) blend films could be changed by controlling the film formation process via using mixed solvents with different evaporation rates. The second solvent, with a higher boiling point than that of the first solvent and much better solubility for PCBM than P3HT, is chosen to mix with the first solvent with a lower boiling point and good solubility for both PCBM and P3HT. The slow evaporation rate of the second solvent provides enough time for PCBM to diffuse upwards during the solvent evaporation. Thus, the weight ratio of PCBM and P3HT ( m PCBM / m P3HT ) at surface of the blend films was varied from ca . 0.1 to ca . 0.72, i.e. , it increases about seven times by changing from single solvent to mixed solvents. Meanwhile, the mixed solvents were in favor to form P3HT naonofiber network and enhance phase separation of P3HT/PCBM blend films. As a result, the power conversion efficiency of the device from mixed solvents with slow evaporation process was about 1.5 times of the one from single solvents.

In this paper, thickness uniformity of poly(9,9-di-n-octylfluorene) films patterned by inkjet printing was improved by the use of solvent mixtures (a solvent with higher volatility, higher surface energy and lower viscosity, with another solvent with lower volatility, lower surface energy and higher viscosity). The average thickness of inkjet printed poly(9,9-di-n-octylfluorene) films was increased from ca. 30 nm to ca. 100 nm when solvent mixtures were used instead of pure chlorobenzene. More flat PFO films were formed instead of the original films with concave-lens like cross-section formed by coffee ring effect. This improvement was explained by combination of intense Marangoni flow at early drying process and weak complementary flow at the later drying process formed in the solvent mixture. Patterned poly(9,9-di-n-octylfluorene) films were used for fabrication of electroluminescence devices with improved electronic property. Array of pixels with about 80% effective light-emitting area was obtained.

The number of micro-sized PCBM aggregations in P3HT/PCBM blend films was reduced by cooling the solution at 0 degrees C. P3HT aggregated when the solution was kept at 0 degrees C for more than 4h. These P3HT aggregations acted as crystal nucleus, resulting in a network of P3HT nanofibers formation in the spin coated films. Then, after thermal annealing the film at 140 degrees C for 1 h, the growth of PCBM micro-size aggregations was efficiently prevented by the dense network of P3HT nanofibers, which was formed before PCBM aggregated. As a result, the density of PCBM micro-size aggregations reduced from 6.2% to 1.0% compared to the room temperature solution. (C) 2013 Elsevier B.V. All rights reserved.

Trace amount (1% to 5%) of polymers [polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(3-hexylthiophene) (P3HT)] are utilized as additives to manipulate the cold crystallization of [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) thin films. Highly crystalline PCBM films made up of well-connected domains and isolated spherulites with tunable size are produced by adjusting the type, molecular weight, and amount of polymer additives. In the nucleation stage, the polymer additives are demonstrated to have a depressing effect on PCBM nucleation. In the growth stage, we suggest that the PCBM growth rate is determined by PCBM molecular diffusion, which is demonstrated to have close correlations with the molecular mobility and crystallinity of the polymer.

The film morphology and nanostructure of the soluble fullerene, [6,6]-phenyl-C(61) butyric acid methyl ester (PCBM), are crucial for its applications in organic thin film devices, such as organic solar cells and organic thin film transistors. In this work, the morphology, structural transformation, and crystallite orientation of PCBM film under thermal annealing as a function of annealing temperature, processing solvents, and solution concentrations are systematically investigated. Crystalline PCBM films with needle-like crystallites, axialitic aggregates, and faceted slices are formed in the annealing process. The axialites, made up of needle-like aggregates, are proposed to be partially developed spherulites frozen at the early growth stage formed through low-angle branching. The faceted slices are found to be PCBM single crystallites with hexagonal packing in the film plane. The film undergoes both amorphous-to-crystalline and crystalline-to-crystalline phase transformations as the annealing temperature is increased. The former transformation, corresponding to the self-organization of disordered PCBM molecules in the kinetically frozen films, occurs at a relative low temperature once the motion of these molecules is thermally activated, whereas the later one, corresponding to the transformation between two thermally stable crystalline phases, occurs when further increasing the annealing temperature. The PCBM crystallites composing these films are found to have an orientation preference normal to the film surface, which can be attributed to the confinement of film thickness for PCBM crystallite growth.

In this paper, low surface energy separators with undercut structures were fabricated through a full-solution process. These low surface energy separators are more suitable for application in inkjet printed passive-matrix displays of polymer light-emitting diodes. A patterned PS film was formed on the P4VP/photoresist film by microtransfer printing firstly. Patterned Au-coated Ni film was formed on the uncovered P4VP/photoresist film by electroless deposition. This metal film was used as mask to pattern the photoresist layer and form undercut structures with the patterned photoresist layer. The surface energy of the metal film also decreased dramatically from 84.6mJ/m2 to 21.1mJ/m2 by modification of fluorinated mercaptan self-assemble monolayer on Au surface. The low surface energy separators were used to confine the flow of inkjet printed PFO solution and improve the patterning resolution of inkjet printing successfully. Separated PFO stripes, complement with the pattern of the separators, formed through inkjet printing. The separators also realized the patterning of cathodes. A passive-matrix display device was obtained through the assistant patterning of low surface energy separators.

The effects of solvent nature on the surface topographies of polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend films spin-coated onto the silicon wafer were investigated. Four different solvents, such as ethylbenzene, toluene, tetrahydrofuran and dichloromethane, were chosen. They are better solvents for PS than that for PMMA. When dichloromethane, tetrahydrofuran and toluene were used, PMMA-rich phase domains protruded from the background of PS. When ethylbenzene was used, PS-rich phase domains elevated on the average height of PMMA-rich phase domains. In addition, continuous pits, networks and isolated droplets consisted of PS formed on the blend film surfaces with the decrease of polymer concentrations. The mechanism of the surface morphology evolution was discussed in detail.

Evaporation of a droplet of silica microsphere suspension on a polystyrene and poly(methyl methacrylate) blend film with isolated holes in its surface has been exploited as a means of particles self-assembly. During the retraction of the contact line of the droplet, spontaneous dewetting combined with the strong capillary force pack the silica microspheres into the holes in the polymer surface. Complex aggregates of colloids are formed after being exposed to acetone vapor. The morphology evolution of the underlying polymer film by exposure to acetone solvent vapor is responsible for the complex aggregates of colloids formation.

Honeycomb macroporous films fabricated by the "breath figures" method were composed of poly2-vinylpyridine (P2VP) distributed in the holes of polystyrene (PS). The porous films exhibited reversible behavior responding to water and different solvent vapors. When the porous film was treated with water, the honeycomb pattern would change to the hexagonal islandlike pattern. Once heated to remove the water, the honeycomb pattern emerged again. When the porous film was exposed to different solvent vapors, the same reversible process appeared. Carbon disulfide (CS(2)), toluene (TOL), and tetrahydrofuran (THF) solvent vapors induced the honeycomb pattern into the ordered islandlike pattern, and ethanol, chloroform, methyl ethyl ketone (MEK), and dimethylformamide (DMF) solvent vapors made the islandlike pattern come back to the honeycomb pattern. The hygroscopic property of P2VP and the polymer-solvent interaction are the driving force for the reversibly switchable morphology. The appropriate control of the hole depth is very crucial in determining the reversible changes.

Ordered hexagonal droplets patterns in phase-separating polymeric blend films of polystyrene and poly(2-vinylpyridine) (PS/PVP) formed due to the convection effect by solvent evaporation. The influences of PS molecular weight, solvent evaporation rate, and the weight ratio of PS to PVP on the PVP-rich domains pattern formation and distributions were investigated by atomic force microscope (AFM). Only in an appropriate range of molecular weight of PS, can the ordered pattern form. Too low or too high molecular weight of PS led no ordered pattern due to the viscosity effects. The increase of solvent evaporation rate decreased the mean radius of the PVP-rich domains and the intervals between the centers of the domains due to the enhancement of the viscosity on the top layer of the fluid film. The increase of the weight ratio of PS to PVP decreased mean radius of the PVP-rich domains whereas the intervals between the centers of droplets remained constant. Therefore, the size and the distributions of ordered patterns can be tuned by the polymer molecular weight, the weight ratio of the two components and the solvent evaporation rate. It revealed that the hydrodynamic effects played a significant role on the pattern formation and distributions.