A simple sheath flow microfluidic device is used to fabricate polymer micro/nanofibers that have precisely controlled shapes and sizes. Poly(methylmethacrylate) (PMMA) was used as the model polymer for these experiments. The sheath-flow device uses straight diagonal and chevron-shaped grooves integrated in the top and bottom walls of the flow channel to move sheath fluid completely around the polymer stream. Portions of the sheath stream are deflected in such a way as to define the cross-sectional shape of the polymer core. The flow-rate ratio between the sheath and core solution determines the fiber diameter. Round PMMA fibers with a diameter as small as 300 nm and flattened fibers with a submicron thickness are demonstrated.

The morphological effects of the incorporation of C60 into blended thin‐films of poly(3‐hexylthiophene) and [6,6]‐phenyl C61 butyric acid methyl ester (PCBM) are investigated. The results show that addition of C60 readily alters the growth‐rate and morphology of PCBM crystallites under different environmental conditions. The effect of C60 on the growth of large PCBM crystallites is thoroughly characterized using optical microscopy, electron microscopy and UV‐visible absorption spectroscopy. Results show that C60 incorporation modifies fullerene aggregation and crystallization and greatly reduces the average crystallite size at C60 loadings of ≈50 wt% in the fullerene phase. Organic field‐effect transistors (OFETs) are prepared to evaluate the electron mobility of PCBM/C60 films and organic solar cells (OSCs) are fabricated from mixed‐fullerene active layers to evaluate their performance. It is demonstrated that the use of fullerene mixtures in organic electronic applications is a viable approach to produce more stable devices and to control the growth of micrometer‐sized fullerene crystals.

Aqueous dispersions of semiconducting nanoparticles have shown promise as a robust and scalable platform for the production of efficient polymer/fullerene active layers in organic photovoltaic applications. Semiconducting nanoparticles are a composite of both an n-type and p-type semiconductor contained within a single nanoparticle. In order to realize efficient organic solar cells from these materials, there is a need to understand how the size and internal distribution of materials within each nanoparticle contributes to photocurrent generation in a nanoparticle-derived device. Therefore, characterizing the internal distribution of conjugated polymer and fullerene within the dispersion is the first step to improving performance. To date, study of polymer/fullerene structure within these nanoparticles has been limited to microscopy techniques of deposited nanoparticles. In this work, we use contrast variation with small-angle neutron scattering to determine the internal distribution of poly(3-hexylthiophene) and [6,6]phenyl-C61-butyric acid methyl ester inside the composite nanoparticles as a function of formulation while in dispersion. On the basis of these measurements, we connect the formulation of these nanoparticles with their internal structure. Using electrostatic deposited monolayers of these nanoparticles, we characterize intrinsic charge generation using photoconductive atomic force microscopy and correlate this with structures determined from small-angle neutron scattering measurements. These techniques combined show that the best performing composite nanoparticles are those that have a uniform distribution of conjugated polymer and fullerene throughout the nanoparticle volume such that electrons and holes are easily transported out of the particle.

High-structured carbon fillers are ubiquitous as the conductive additive comprising suspension-based electrochemical energy storage technologies. Carbon black networks provide the necessary electrical conductivity as well as mechanical percolation in the form of a yield stress. Despite their critical role in determining system performance, a full mechanistic understanding of the relationship between the electrical transport characteristics of the percolated, conductive networks of carbon black, and the rheological properties is lacking, which hinders the rational design and optimization of flowable electrodes and the processing of electrolytes for batteries. Here, we report on the microstructural origin of the rheological and electrical properties of two commonly used conductive additives in neat propylene carbonate. From quiescent mechanical and structural studies, we find that the gelation of these carbon black suspensions is best described by the dynamic arrest of a clustered fluid phase. In contrast, the temperature and frequency dependence of the ac conductivity near this transition shows that mesoscale charge transport is determined by hopping between localized states that does not require a stress-bearing network. This unique combination of microstructural characterization with rheological and electrical measurements enables testing prevailing theories of the connection between electrical and mechanical percolation as well as improving conductive additives to enhance electrochemical performance.

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Using an analysis based on Marcus theory, we characterize losses in open-circuit voltage (V OC ) due to changes in charge-transfer state energy, electronic coupling, and spatial density of charge-transfer states in a series of polymer/fullerene solar cells. We use a series of indacenodithiophene polymers and their selenium-substituted analogs as electron donor materials and fullerenes as the acceptors. By combining device measurements and spectroscopic studies (including subgap photocurrent, electroluminescence, and, importantly, time-resolved photoluminescence of the chargetransfer state) we are able to isolate the values for electronic coupling and the density of charge-transfer states (N CT ), rather than the more commonly measured product of these values. We find values for N CT that are surprisingly large (∼4.5 × 10 21 −6.2 × 10 22 cm −3 ), and we find that a significant increase in N CT upon selenium substitution in donor polymers correlates with lower V OC for bulk heterojunction photovoltaic devices. The increase in N CT upon selenium substitution is also consistent with nanoscale morphological characterization. Using transmission electron microscopy, selected area electron diffraction, and grazing incidence wide-angle X-ray scattering, we find evidence of more intermixed polymer and fullerene domains in the selenophene blends, which have higher densities of polymer/fullerene interfacial charge-transfer states. Our results provide an important step toward understanding the spatial nature of charge-transfer states and their effect on the open-circuit voltage of polymer/fullerene solar cells.

We have combined fusion of oligomers with cyclic symmetry and alanine substitutions to eliminate clashes and produce proteins that self-assemble into 2-D arrays upon addition of calcium ions. Using TEM, AFM, small-angle X-ray scattering, and fluorescence microscopy, we show that the designed lattices which are 5 nm high with p3 space group symmetry and 7.25 nm periodicity self-assemble into structures that can exceed 100 μm in characteristic length. The versatile strategy, experimental approach, and hexagonal arrays described herein should prove valuable for the engineering of functional nanostructured materials in 2-D.

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