Energy Focus: Polymer series enables all-polymer solar cells
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tructures generated from the assembly of metallic nanoparticles (NPs) have garnered significant attention due to their potential technological applications. Now, an international research group has developed strategies which can generate linear assemblies of anisotropic gold nanorods (NRs). Linkage of nanorods with different dimensions led to random and block copolymer structures. The group’s approach was further extended to the co-assembly of random copolymers of gold and palladium NRs. Eugenia Kumacheva of the University of Toronto, Kun Liu of Jilin University, China, Michael Rubenstein of the University of North Carolina, and their colleagues describe their copolymerization methodologies in the March 3 issue of Angewandte Chemie International Edition (DOI: 10.1002/anie.201309718; p. 2648). Gold NRs with mean diameter
Energy Focus Polymer series enables all-polymer solar cells
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rganic photovoltaics have captured much attention because they are lightweight and mechanically flexible, allowing them to occupy new niches for solar power like integration with clothing and building materials. They are also manufactured using a low-cost, roll-toroll process, which is key if they are to successfully compete with silicon-based PV. However, one limitation is the current requirement for relatively costly fullerenes as the electron acceptor material. Now, H. Huang and colleagues at Northwestern University, the University of the Chinese Academy of Sciences, the University of Málaga, and Polyera Corporation have synthesized and characterized a new series of alkoxy-functionalized, π-conjugated polymers that show significant promise for use as electron
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MRS BULLETIN
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VOLUME 39 • JUNE 2014
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of 12 nm and lengths of 99 nm were etched to fine-tune their lengths, and were then functionalized with thiol-terminated polystyrene (PS) molecules. End-to-end association of NRs, which behave as monomers, is initiated when the quality of the solvent for the PS tethers is reduced by adding water to the solution of PS-functionalized NRs in dimethylformamide (DMF). When the process is repeated with a mixture of short 50-nm in length NRs (SNRs) and 80-nm long NRs (LNRs), co-assembly into linear copolymer structures with limited extent branching is revealed in scanning transmission electron microscopy (STEM) images. The researchers also used strategies commonly employed in the synthesis of molecular block copolymers to coassemble block copolymer structures from gold SNRs and LNRs. In the two-prepolymer approach, homopolymer structures from SNRs and LNRs are separately prepared in DMF/water mixture. Upon mixing the solutions of the homopolymers, the chains of SNRs and LNRs copolymerize to give large
fractions of diblock and triblock copolymers. In the one-prepolymer approach, individual SNRs are introduced right after the assembly of LNR homopolymer in a water/DMF mixture. Analysis of STEM images reveal that the SNR monomers primarily attach to the ends of the LNR blocks or to each other. Palladium NRs with mean lengths and diamet
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