Hierarchical Ni–Co Hydroxide Petals on Mechanically Robust Graphene Petal Foam for High‐Energy Asymmetric Supercapacitors

A hierarchical structure consisting of Ni–Co hydroxide nanopetals (NCHPs) grown on a thin free‐standing graphene petal foam (GPF) has been designed and fabricated by a two‐step process for pseudocapacitive electrode applications. The mechanical behavior of GPFs has been, for the first time to our knowledge, quantitatively measured from in situ scanning electron microscope characterization of the petal foams during in‐plane compression and bending processes. The Young's modulus of a typical GPF is 3.42 GPa, indicating its outstanding mechanical robustness as a nanotemplate. The GPF/NCHP electrodes exhibit volumetric capacitances as high as 765 F cm^?3, equivalent to an areal capacitance of 15.3 F cm^?2 and high rate capability. To assess practical functionality, two‐terminal asymmetric solid‐state supercapacitors with 3D GPF/NCHPs as positive electrodes are fabricated and shown to exhibit outstanding energy and power densities, with maximum average energy density of ≈10 mWh cm^?3 and maximum power density of ≈3 W cm^?3, high rate capability (a capacitance retention of ≈60% at 100 mA cm^?2), and excellent long‐term cyclic stability (full capacitance retention over 15 000 cycles).     

Printed semi-transparent large area organic photovoltaic modules with power conversion efficiencies of close to 5 %

Currently, certified lab scale organic photovoltaic (OPV) cells reach efficiencies of more than 12% and life times of 10 years. For commercialization, it is necessary to understand which performance can be reached in fully printed large scale products. Our investigations show that large area, semi-transparent organic photovoltaic modules based on industrially available materials can achieve power conversion efficiencies of more than 4.8% on rigid substrates and 4.3% on flexible ones. The modules processed with a combination of large area coating and laser patterning with an active area of 68.76 cm² for flexible modules and a total area of 197.4 cm² for glass modules offer exceptionally high geometric fill factors of more than 94% and a transparency of more than 10%. The processing recipe and the layout of the modules are based on indications of optical and electrical simulations which allow to produce devices with only negligible losses in comparison to small single cell devices. Losses due to imperfect coating or patterning are identified by thermal imaging.     

Novel Film‐Casting Method for High‐Performance Flexible Polymer Electrodes

A new film‐casting method for polymer electrodes is reported, in which thickness‐controlled drop‐casting (TCDC), using polyaniline doped with camphorsulfonic acid (PANI:CSA) is used. By combining the advantages of conventional spin‐casting and drop‐casting methods, and by rigorously controlling the film formation parameters, flexible polymer electrodes with high conductivity and excellent transmittance can be produced. The PANI:CSA electrodes cast by the TCDC method exhibited constant thickness‐independent conductivities of ～600 S cm^?1 down to a film thickness of 0.2 μm, and a high optical transmittance of about 85% at 550 nm. Furthermore, the new casting method significantly reduced the sheet resistance (～90 Ω/square) of the PANI:CSA electrodes compared with the conventional spin‐cast films, enhancing the performance of the devices deposited on plastic substrates. The flexible polymer light‐emitting diode produced a brightness of 6000 cd m^?2, and the flexible polymer solar cell exhibited a power conversion efficiency of 2%, both of which were much higher than those of the devices fabricated by the conventional spin‐casting method.     

In Situ Studies of Ion Transport in Microporous Supercapacitor Electrodes at Ultralow Temperatures

The ability to quickly store and deliver a significant amount of electrical energy at ultralow temperatures is critical for the energy‐efficient operation of high altitude aircraft and spacecraft, exploration of natural resources in polar regions and extreme altitudes, and astronomical observatories exposed to ultralow temperatures. Commercial high‐power electrochemical capacitors fail to operate at temperatures below –40 °C. According to conventional wisdom, mesoporous electrochemical capacitor electrodes with pores large enough to accommodate fully solvated ions are needed for sufficiently rapid ion transport at lower temperatures. It is demonstrated that strictly microporous carbon electrodes with much higher volumetric capacitance can be efficiently used at temperatures as low as –70 °C. The critical parameters, with respect to electrolyte properties and electrode porosity and microstructure, needed for achieving both rapid ion transport and efficient ion electroadsorption in porous carbons are discussed. As an example, the fabrication of an electrochemical capacitor with an outstanding performance at temperatures as low as –60 and –70 °C is demonstrated. At such low temperatures the capacitance of the synthesized electrodes is up to 123 F g^?1 (≈76 F cm^?3), which is 50–100% higher than that of the most common commercial electrochemical capacitor electrode at room temperature. At –60 °C selected cells based on ≈0.2 mm electrodes exhibited characteristic charge–discharge time constants of less than 9 s, which is faster than the majority of commercial devices at room temperature. The achieved combination of high energy and power densities at such ultralow temperatures is unprecedented and extremely promising for the advancement of energy storage systems.     

Ever‐Increasing Pseudocapacitance in RGO–MnO–RGO Sandwich Nanostructures for Ultrahigh‐Rate Lithium Storage

Lithium ion batteries have attained great success in commercialization owing to their high energy density. However, the relatively delaying discharge/charge severely hinders their high power applications due to intrinsically diffusion‐controlled lithium storage of the electrode. This study demonstrates an ever‐increasing surface redox capacitive lithium storage originating from an unique microstructure evolution during cycling in a novel RGO–MnO–RGO sandwich nanostructure. Such surface pseudocapacitance is dynamically in equilibrium with diffusion‐controlled lithium storage, thereby achieving an unprecedented rate capability (331.9 mAh g^?1 at 40 A g^?1, 379 mAh g^?1 after 4000 cycles at 15 A g^?1) with outstanding cycle stability. The dynamic combination of surface and diffusion lithium storage of electrodes might open up possibilities for designing high‐power lithium ion batteries.     

Realization of high performance large area Z‐series‐interconnected opaque dye solar cell modules

We have designed and fabricated dye solar cell (DSC) modules with optimized geometries and processes. Integrated interconnections were made following the “Z” architecture for series connections. Several modules were prepared varying the materials, multilayer combination of the TiO₂ active layers, and the fabrication processes. With the best combination of TiO₂ multilayers, titanium tetrachloride (TiCl₄) treatment, a back reflector/diffusor, and optimized layout of cells via simulations, we fabricated a DSC module with a conversion efficiency of 6.9% on 43 cm² aperture area and 9.4% on active area. This result confirms that an effective scale‐up of high performance Z‐series‐connected DSC modules can be achieved comparable with other thin film technology. Note that the materials used to produce the devices of this work are all commercially available: an important result for a technology that is being developed for industrial application. Copyright © 2012 John Wiley & Sons, Ltd.     

High efficiency ITO-free flexible white organic light-emitting diodes based on multi-cavity technology

The technology of white organic light-emitting diodes (WOLEDs) is attracting growing interest due to their potential application in indoor lighting. Nevertheless the simultaneous achievement of high luminous efficacy (LE), high color rendering index (CRI), very low manufacturing costs and compatibility with flexible thin substrates is still a great challenge. Indeed, very high efficiency devices show usually low values of CRI, not suitable for lighting applications, and use expensive indium tin oxide (ITO) electrodes which are not compatible with low cost and/or flexible products. Here we show a novel low cost ITO-free WOLED structure based on a multi-cavity architecture with increased photonic mode density and still broad white emission spectrum, which allows for simultaneous optimization of all device characteristics. Without using out-coupling optics or high refractive index substrates, CRI of 85 and LE as high as 33 lm W⁻¹ and 14 lm W⁻¹ have been demonstrated on ITO-free glass and flexible substrates, respectively.     

Simultaneous Electrochemical Dual‐Electrode Exfoliation of Graphite toward Scalable Production of High‐Quality Graphene

Developing scalable methods to produce large quantities of high‐quality and solution‐processable graphene is essential to bridge the gap between laboratory study and commercial applications. Here an efficient electrochemical dual‐electrode exfoliation approach is developed, which combines simultaneous anodic and cathodic exfoliation of graphite. Newly designed sandwich‐structured graphite electrodes which are wrapped in a confined space with porous metal mesh serve as both electrodes, enabling a sufficient ionic intercalation. Mechanism studies reveal that the combination of electrochemical intercalation with subsequent thermal decomposition results in drastic expansion of graphite toward high‐efficiency production of graphene with high quality. By precisely controlling the intercalation chemistry, the two‐step approach leads to graphene with outstanding yields (85% and 48% for cathode and anode, respectively) comprising few‐layer graphene (1–3 layers, >70%), ultralow defects (I_D/I_G < 0.08), and high production rate (exceeding 25 g h^?1). Moreover, its excellent electrical conductivity (>3 × 10⁴ S m^?1) and great solution dispersibility in N‐methyl pyrrolidone (10 mg mL^?1) enable the fabrication of highly conductive (11 Ω sq^?1) and flexible graphene films by inkjet printing. This simple and efficient exfoliation approach will facilitate the development of large‐scale production of high‐quality graphene and holds great promise for its wide application.     

Patterning of organic photovoltaic modules by ultrafast laser

In this paper, we demonstrate that laser patterning of organic solar cells by ultrafast laser systems (pulse length <350 fs) is an attractive process to produce photovoltaic modules with outstanding high geometric fill factors. Moreover, in terms of precision, registration, and debris generation and in terms of keeping the damage to the underneath layers at a minimum, ultrafast laser patterning with a pulse length of few hundreds of femtoseconds turns out to yield superior results. Ablation of all three different solar cell layers (electrodes (P1 and P3) and interfaces and semiconductor (P2)) is achieved with a single wavelength simply by a precise adjustment of the laser fluence and the patterning overlap. Camera positioning allows a precise registration between the various processing steps and a reduction of the width of the overall interconnection regime to the hundreds of micrometers dimension, resulting in high geometrical fill factors of over 90% for monolithically interconnected organic solar cell modules. Copyright © 2013 John Wiley & Sons, Ltd.     

Transfer printing approach to all-carbon nanoelectronics

Transfer printing methods are used to pattern and assemble monolithic carbon nanotube (CNT) thin-film transistors on large-area transparent, flexible substrates. Airbrushed CNT thin-films with sheet resistance 1 kΩ sq⁻¹ at 80% transparency were used as electrodes, and high quality chemical vapor deposition (CVD)-grown CNT networks were used as the semiconductor component. Transfer printing was used to pre-pattern and assemble thin film transistors on polyethylene terephthalate (PET) substrates which incorporated Al₂O₃/poly-methylmethacrylate (PMMA) dielectric bi-layer. CNT-based ambipolar devices exhibit field-effect mobility in range 1-33 cm²/V s and on/off ratio ∼10³, comparable to the control devices fabricated using Au as the electrode material.