The Application of Highly Doped Single-Layer Graphene as the Top Electrodes of Semitransparent Organic Solar Cells

Zhike Liu, Jinhua Li, Zhen-Hua Sun, Guoan Tai, Shu-Ping Lau, and Feng Yan*

Department of Applied Physics and Materials Research Centre, The Hong Kong Polytechnic University, Hong Kong, China

ACS Nano, Article ASAP

DOI: 10.1021/nn204675r

Publication Date (Web): December 11, 2011

A single-layer graphene film with high conductance and transparency was realized by effective chemical doping. The conductance of single-layer graphene was increased for more than 400% when it was doped with Au nanoparticles and poly(3,4-ethylenedioxythiophene): poly(styrene sulfonic acid). Then semitransparent organic solar cells based on poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) were fabricated with single-layer graphene and indium tin oxide (ITO) as the top and bottom electrodes, respectively. The performance of the devices was optimized by tuning the active layer thickness and doping the single-layer graphene electrodes. The maximum efficiency of 2.7% was observed in the devices with the area of 20 mm² illuminated from graphene electrode under the AM1.5 solar simulator. It is notable that all of the devices showed higher efficiency from the graphene than ITO side, which was attributed to the better transmittance of the graphene electrodes. In addition, the influence of the active area of the organic solar cell on its photovoltaic performance was studied. We found that, when the active areas increased from 6 to 50 mm², the power conversion efficiencies decreased from 3% to 2.3% because of the increased series resistances and the decreased edge effect of the devices.

Microdrop Printing of Hydrogel Bioinks into 3D Tissue-Like Geometries

1. Kris Pataky¹, 
2. Thomas Braschler¹, 
3. Andrea Negro², 
4. Philippe Renaud¹, 
5. Matthias P. Lutolf^2,*, 
6. Juergen Brugger^1,*

Article first published online: 12 DEC 2011

DOI: 10.1002/adma.201102800

An optimized 3D inkjet printing process is demonstrated for structuring alginate into a tissue-like microvasculature capable of supporting physiological flow rates. Optimizing the reaction at the single-droplet level enables wet hydrogel droplets to be stacked, thus overcoming their natural tendancy to spread and coalesce. Live cells can be patterned using this process and it can be extended to a range of other hydrogels.

Nanoreactors for Studying Single Nanoparticle Coarsening

Jinan Chai†‡, Xing Liao‡§, Louise R. Giam‡§, and Chad A. Mirkin*†‡§

^†Department of Chemistry, ^‡International Institute for Nanotechnology, and ^§Department of Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja2097964

The ability to observe intermediate structures as part of coarsening processes that lead to the formation of single nanoparticles (NPs) is important in gaining fundamental insight pertaining to nanostructure growth. Here, we use scanning probe block copolymer lithography (SPBCL) to create “nanoreactors” having attoliter volumes, which confine Au NP nucleation and growth to features having diameters <150 nm on a substrate. With this technique, one can use in situ TEM to directly observe and study NP coarsening and differentiate Ostwald ripening from coalescence processes. Importantly, the number of metal atoms that can engage in coarsening can be controlled with this technique, and TEM “snapshots” of particle growth can be taken. The size of the resulting nanostructures can be controlled in the 2–10 nm regime.

DNA as Invisible Ink for AFM Nanolithography

Jian Liang†, Matteo Castronovo†‡, and Giacinto Scoles*†

Department of Biology, Temple University, 1900 North 12th Street, Philadelphia, Pennsylvania 19122, United States

Experimental and Clinical Pharmacology Unit, CRO-National Center Institute, Via Franco Gallini 2, I-33081 Aviano Pordenone, Italy

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja2076845

We have used nanografting, an atomic force microscopy (AFM)-based nanolithography technique, to fabricate thiolated DNA nanostructures on gold surfaces. The tip-guided assembly offers opportunities for locally controlling the packing order, density, and thus the thickness of the DNA patterns. By selecting proper nanografting parameters, we can embed single-stranded DNA (ssDNA) patches into a background composed of the same DNA molecule prepared by self-assembly, in which the patches remain topographically (and chemically) invisible but have much improved packing order. When the complementary DNA (cDNA) is added, the thickness of the nanografted layer increases much more dramatically than that of the self-assembled layer during the hybridization process, and as a result, the pattern emerges. Interestingly, the pattern can be reversibly hidden and shown with high fidelity simply by dehybridizing and appending the cDNA repeatedly.

Confinement-Guided Shaping of Semiconductor Nanowires and Nanoribbons: “Writing with Nanowires”

Alexander Pevzner, Yoni Engel, Roey Elnathan, Alexander Tsukernik, Zahava Barkay, and Fernando Patolsky*

School of Chemistry, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel-Aviv University, Tel Aviv 69978, Israel

Nano Lett., Article ASAP

DOI: 10.1021/nl201527h

To fully exploit their full potential, new semiconductor nanowire building blocks with ab initio controlled shapes are desired. However, and despite the great synthetic advances achieved, the ability to control nanowire’s geometry has been significantly limited. Here, we demonstrate a simple confinement-guided nanowire growth method that enables to predesign not only the chemical and physical attributes of the synthesized nanowires but also allows a perfect and unlimited control over their geometry. Our method allows the synthesis of semiconductor nanowires in a wide variety of two-dimensional shapes such as any kinked (different turning angles), sinusoidal, linear, and spiral shapes, so that practically any desired geometry can be defined. The shape-controlled nanowires can be grown on almost any substrate such as silicon wafer, quartz and glass slides, and even on plastic substrates (e.g., Kapton HN).

Nanoscale Localization Sampling Based on Nanoantenna Arrays for Super-resolution Imaging of Fluorescent Monomers on Sliding Microtubu

1. Kyujung Kim¹, 
2. Junichiro Yajima², 
3. Youngjin Oh¹, 
4. Wonju Lee¹, 
5. Shinsuke Oowada³,
6. Takayuki Nishizaka^3,*, 
7. Donghyun Kim^1,*

Article first published online: 14 DEC 2011

DOI: 10.1002/smll.201101840

Sub-diffraction-limited imaging of fluorescent monomers on sliding microtubules in vitro by nanoscale localization sampling (NLS) is reported. NLS is based on periodic nanohole antenna arrays that create locally amplified electromagnetic hot spots through surface plasmon localization. The localized near-field hot spot temporally samples microtubular movement for enhanced spatial resolution. A fourfold improvement in spatial resolution compared to conventional wide-field microscopy is demonstrated. The resolution enhancement is achieved by imaging rhodamine-labeled microtubules that are sampled by the hot spots to provide sub-diffraction-limited images at 76 nm resolution in the direction of movement and 135 nm orthogonally. The intensity distribution produced by the NLS is measured to be broader than that of conventional imaging, which is consistent with the improvement of imaging resolution. Correlation studies between neighboring nanoantennas are also performed. This confirms the possibility of measuring microtubular transport dynamics. NLS can be useful for moving objects that have a high labeling density or for performing fluctuation spectroscopy in small volumes, and may allow “super-resolution on demand” by customizing nanoantenna structures for specific resolution needs

Printing: Fabrication and Characterization of Cytocompatible Polypyrrole Films Inkjet Printed from Nanoformulations Cytocompatible, Inkjet-Printed Polypyrrole Films

1. Bo Weng, 
2. Xiao Liu, 
3. Michael J. Higgins,
4. Roderick Shepherd, 
5. Gordon Wallace

Article first published online: 12 DEC 2011

DOI: 10.1002/smll.201190097

The utility of polypyrrole (PPy) as an interface to cells in a variety of applications including tissue engineering scaffolds and neural electrodes has been demonstrated; however, rapid micropatterning methods for processing such devices from PPy are yet to be fully realized. Inkjet printing is a rapid low-cost technology for the fabrication of thin films and microstructures at a typical resolution of 50–100 μm. In light of this, a stable inkjet-printable PPy nanodispersion doped with a gemini surfactant has been developed for inkjet printing. The cover image depicts inkjet printing of conductive cytocompatible PPy films from this nanoformulation. PC 12 cells are used to demonstrate the cytocompatibility of the inkjet-printed films. This novel approach to fabricating conductive PPy surfaces for tissue engineering is particularly useful where microstructures are required

Receptor-Mediated Endocytosis of Nanoparticles of Various Shapes

Cellular uptake through endocytosis is crucial for drug delivery and nanomedicine. However, the conditions under which passive endocytosis (i.e., not ATP driven) takes place are not well understood. We report MD simulations of the passive uptake of ligand-coated nanoparticles with varying size, shape, coverage, and membrane-binding strength. We find that the efficiency of passive endocytosis is higher for spherocylindrical particles than for spheres and that endocytosis is suppressed for particles with sharp edges.

Functionalized Multilayered Graphene Platform for Urea Sensor

Multilayered graphene (MLG) is an interesting material for electrochemical sensing and biosensing because of its very large 2D electrical conductivity and large surface area. We propose a less toxic, reproducible, and easy method for producing functionalized multilayer graphene from multiwalled carbon nanotubes (MWCNTs) in mass scale using only concentrated H₂SO₄/HNO₃. Electron microscopy results show the MLG formation, whereas FTIR and XPS data suggest its carboxylic and hydroxyl-functionalized nature. We utilize this functionalized MLG for the fabrication of a novel amperometric urea biosensor. This biosensor shows linearity of 10–100 mg dL^–1, sensitivity of 5.43 μA mg^–1 dL cm^–2, lower detection limit of 3.9 mg dL^–1, and response time of 10 s. Our results suggest that MLG is a promising material for electrochemical biosensing applications.

Drop-Casted Self-Assembling Graphene Oxide Membranes for Scanning Electron Microscopy on Wet and Dense Gaseous Samples

Graphene oxide sheets dispersed in water and many other solvents can spontaneously assemble into a surface film covering an evaporating droplet due to their amphiphilicity. Thus, graphene oxide membranes with controllable thickness suspended over an orifice have been directly fabricated using a simple drop-cast approach. Mechanical properties and electron transparency tests of these membranes show their use as electron transparent, but molecularly impenetrable, windows for environmental electron microscopy in liquids and dense gaseous media. The foreseeable, broader application of this drop-cast window methodology is the creation of access spots for electron probes to study isolated microsamples in their natural, undisrupted state within the interior of prefabricated devices (such as microfluidic chips or sealed containers of biological, chemically reactive, toxic, or forensic materials).

Toward a Light-Driven Motorized Nanocar: Synthesis and Initial Imaging of Single Molecules

A second generation motorized nanocar was designed, synthesized, and imaged. To verify structural integrity, NMR-based COSY, NOESY, DEPT, HSQC, and HMBC experiments were conducted on the intermediate motor. All signals in ¹H NMR were unambiguously assigned, and the results were consistent with the helical structure of the motor. The nanocar was deposited on a Cu(111) surface, and single intact molecules were imaged by scanning tunneling microscopy (STM) at 5.7 K, thereby paving the way for future single-molecule studies of this motorized nanocar atop planar substrates.

Bacterial Isolation by Lectin-Modified Microengines

New template-based self-propelled gold/nickel/polyaniline/platinum (Au/Ni/PANI/Pt) microtubular engines, functionalized with the Concanavalin A (ConA) lectin bioreceptor, are shown to be extremely useful for the rapid, real-time isolation of Escherichia coli (E. coli) bacteria from fuel-enhanced environmental, food, and clinical samples. These multifunctional microtube engines combine the selective capture of E. coli with the uptake of polymeric drug-carrier particles to provide an attractive motion-based theranostics strategy. Triggered release of the captured bacteria is demonstrated by movement through a low-pH glycine-based dissociation solution. The smaller size of the new polymer-metal microengines offers convenient, direct, and label-free optical visualization of the captured bacteria and discrimination against nontarget cells.

Highly Efficient White Top-Emitting Organic Light-Emitting Diodes Comprising Laminated Microlens Films

White top-emitting organic light-emitting diodes (OLEDs) attract much attention, as they are optically independent from the substrate used. While monochrome top-emitting OLEDs can be designed easily to have high-emission efficiency, white light emission faces obstacles. The commonly used thin metal layers as top electrodes turn the device into a microresonator having detrimental narrow and angular dependent emission characteristics. Here we report on a novel concept to improve the color quality and efficiency of white top-emitting OLEDs. We laminate a refractive index-matched microlens film on the top-emitting device. The microlens film acts both as outcoupling-enhancing film and an integrating element, mixing the optical modes to a broadband spectrum.