No abstract

No abstract

Organic and polymeric photovoltaic (PV) cells show promise as low-cost, lightweight, flexible, and renewable energy sources and have been extensively investigated during the past decade. [1] Recently, tremendous progress was made in the development of bulk heterojunction organic PV cells based on p-conjugated polymers as electron donor ( p-type) materials, i.e., regioregular poly(3-alkylthiophene)s (P3HTs), blended with soluble fullerenes (C 60 ) as electron acceptor (n-type) materials, i.e., [6,6]-phenyl C 61 -butyric acid methyl ester (PCBM). With an accurate control of the formation of the nanostructure of the interpenetrating donor/acceptor polymer network by means of limiting the solvent evaporation rate or by post-fabrication thermal annealing, power conversion efficiencies (PCE) greater than 5% were achieved.[2] Meanwhile, multilayer heterojunction PV cells that are based on small molecules also advanced significantly through the use of new optimized device architectures, e.g., tandem or dual dye-doped structures, with efficiencies reportedly being as high as 5.6%. [3] However, in order to further enhance the PCEs of heterojunction PV cells it is of paramount importance to develop novel organic and polymer semiconductors exhibiting a narrow optical gap as well as a high charge carrier mobility to harvest the majority of sunlight radiation and efficiently transport the photogenerated charges to the electrodes. [1d,e] Triarylamines, which are well-known to have high holetransport mobilities and form stable cation radicals, are widely used as hole-transporting materials in organic light emitting diodes (LED), [4] and show potential as molecular based magnets. [5] Recently, it was demonstrated that light emitting molecules/ polymers which are incorporated or end-capped with diarylamine/triarylamine moieties exhibit a greatly enhanced LED device performance. [6] In order to further improve the light harvesting efficiency of a hole-transporting triarylamine, hence enable its efficient application in photovoltaics, it is necessary to reduce its optical energy gap to better match the solar spectrum. The use of electron-accepting dicyanovinyl groups to introduce the low-lying LUMO of triarylamine derivatives into p-type semiconducting star-shaped molecules thereby reducing the optical energy gap has been reported.[7]Herein, we report the synthesis and characterization of novel hole-transporting and narrow HOMO-LUMO energy gap oligothiophenes that are asymmetrically endcapped with diphenylaminofluorenyl and dicyanovinyl groups, i.e., PhN-OFOT(n)-DCN (n ¼ 2-4), and their potential for photovoltaic applications. The incorporation of triarylamino-donors and dicyanovinylacceptors greatly reduces the optical energy gap of oligothiophene thin-films to 1.82-1.92 eV, while the first ionization energy remains high with $5.2 eV, which is important in obtaining high open-circuit voltages (V oc ) as well as improving air stability. An increase in oligothiophene length provides stronger light absorption and promotes better ...

Novel low optical gap, p-type semiconducting oligothiophenes asymmetrically end-capped with triarylamino and tricyanovinyl groups, PhN-OFOT(n)-TCN (n ) 2, 3), have been synthesized and characterized for photovoltaic applications. With an incorporation of a tricyanovinyl accepting group to the triarylamine, the optical energy gap greatly reduces to 1.46 eV and the LUMO level lowers to 3.9 eV. The initial studies of the bilayer heterojunction PV cells based on the newly developed tricyanovinyl-substituted chromophores as a donor material and C 60 as an acceptor material showed a PCE up to 1.33% with a large open-circuit voltage of 0.82 V in the annealed devices which makes this class of materials promising for further development. Our findings also suggest for the first time that the tricyanovinyl group is highly efficient to lower the LUMO level and reduce the optical energy gap of a p-type semiconducting photosensitizer. It is interesting to find that PhN-OFOT(2)-TCN showed better device performance in bilayer solar cells than PhN-OFOT(3)-TCN although the latter has a slightly narrower optical gap. Since the LUMO energy level of PhN-OFOT(3)-TCN (ca. 3.9 eV vs vacuum) is too close to that of C 60 (4.0 eV), the yield of photoinduced charge carriers was low, leading to a low power conversion efficiency. Our findings highlight the importance of a large LUMO level offset between electron donors and acceptors to the achievement of high performance organic solar cells.

No abstract

Interface devices such as integrated planar patch‐clamp chips are being developed to study the electrophysiological activity of neuronal networks grown in vitro. The utility of such devices will be dependent upon the ability to align neurons with interface features on the chip by controlling neuronal placement and by guiding cell connectivity. In this paper, we present a strategy to accomplish this goal. Patterned chemical modification of SiN surfaces with poly‐d‐lysine transferred from PDMS stamps was used to promote adhesion and guidance of cryo‐preserved primary rat cortical neurons. We demonstrate that these neurons can be positioned and grown over microhole features which will ultimately serve as patch‐clamp interfaces on the chip. Biotechnol. Bioeng. 2010; 105: 368–373. © 2009 Wiley Periodicals, Inc.

Received May 4, 2009; Revised Manuscript Received July 6, 2009 ABSTRACT: Low-bandgap regioregular polythiophene derivatives, PTh 6 BTD, PTh 8 BTD, and PTh 4 TTBTD, were synthesized through Stille coupling reaction. These are alternating copolymers of an electron-deficient benzothiadiazole unit and oligothiophene units including hexathiophene, octathiophene, and thieno[3,2-b]thiophene-bridged quarterthiophene, respectively. The polymers are soluble in halogenated solvents such as o-dichlorobenzene, affording good processability in solar cell fabrication. Meanwhile, the synthesized alternating copolymers show much broader absorption than P3HT, covering the spectral region from 350 to 800 nm. DSC analysis showed that all three polymers readily crystallized, indicating highly ordered intermolecular packing, which is beneficial for achieving higher charge carrier mobility. Bulkheterojunction solar cells using 1:1 w/w PTh n BTD:PC 61 BM ([6,6]-phenyl C 61 -butyric acid methyl ester) blends as the photovoltaic active layers were fabricated and characterized. Best power conversion efficiency of 1.7% was obtained from PTh 8 BTD-based devices under a simulated AM 1.5 G solar irradiation of 100 mW/cm 2 .

No abstract