SC Device Research Articles

Aqueous electrostatic dispersion and heterocoagulation of multiwalled carbon nanotubes and manganese dioxide for the fabrication of supercapacitor electrodes and devices

A conceptually new approach has been developed for the fabrication of MnO2-multiwalled carbon nanotube (MWCNT) composites for electrodes of electrochemical supercapacitors (ES). Benzyldimethylhexadecylammonium chloride (BAC) surfactant and caffeic acid (CA) selectively adsorbed on MWCNT and MnO2, respectively, and allowed the formation of stable aqueous suspensions of positively charged MWCNT and negatively charged MnO2. The comparison of the electrophoretic deposition yield data for BAC, CA and other molecules provided an insight into the influence of the molecular structure on adsorption of the molecules and dispersion of MWCNT and MnO2. Advanced composite materials with good mixing of the individual components were obtained by heterocoagulation, based on an ion-pairing assembly of BAC and CA. The composite electrodes, prepared by the new method showed superior electrochemical performance. It was found that high capacitance and good capacitance retention at high charge–discharge rates can be achieved at high active mass loadings. A practical outcome of this study was the fabrication of an asymmetric SC device, containing a positive MnO2–MWCNT electrode and negative activated carbon–carbon black composite electrode with a voltage window of 1.8 V in an aqueous electrolyte. The asymmetric device showed high capacitance, high power-energy characteristics, good capacitance retention at high charge–discharge rates and cyclic stability.

High Energy Density Asymmetric Quasi-Solid-State Supercapacitor Based on Porous Vanadium Nitride Nanowire Anode

To push the energy density limit of asymmetric supercapacitors (ASCs), a new class of anode materials is needed. Vanadium nitride (VN) holds great promise as anode material for ASCs due to its large specific capacitance, high electrical conductivity, and wide operation windows in negative potential. However, its poor electrochemical stability severely limits its application in SCs. In this work, we demonstrated high energy density, stable, quasi-solid-state ASC device based on porous VN nanowire anode and VOx nanowire cathode for the first time. The VOx//VN-ASC device exhibited a stable electrochemical window of 1.8 V and excellent cycling stability with only 12.5% decrease of capacitance after 10,000 cycles. More importantly, the VOx//VN-ASC device achieved a high energy density of 0.61 mWh cm(-3) at current density of 0.5 mA cm(-2) and a high power density of 0.85 W cm(-3) at current density of 5 mA cm(-2). These values are substantially enhanced compared to most of the reported quasi/all-solid-state SC devices. This work constitutes the first demonstration of using VN nanowires as high energy anode, which could potentially improve the performance of energy storage devices.

Dynamic Simulation of HTSC Cables With a Conventional Simulation Program

The recent development, achieved on SC devices for grid applications, requires the support of design tools in order to establish the impact of these new devices on the operation of the electrical system. Classically, standard simulation programs are used in grid design and maintenance by the utilities; but these new devices require user written models, compatible with the grid simulators. In this paper, a user written model for the integration of superconducting cables in the grid, with the capacity to simulate dynamic behavior, is presented. Results of the simulations are presented which refer to the overall grid performance.

Oxide/polymer interfaces for hybrid and organic solar cells: Anatase vs. Rutile TiO 2

In this work, we study the effect of the transparent conducting oxide (TCO) and the polymer applied (MEH-PPV or P3HT) on the photovoltaic properties of TCO/TiO 2/polymer/Ag bi-layer solar cells. The solar cells were analyzed under inert atmosphere conditions resembling an encapsulated or sealed device. We demonstrate that the substrate applied, ITO or FTO, modifies the crystalline structure of the TiO 2: on an ITO substrate, TiO 2 is present in its anatase phase, on an FTO, the rutile phase predominates. Devices fabricated on an FTO, where the rutile phase is present, show better stability under inert atmospheres than devices fabricated on an ITO, anatase phase. With respect to the polymer, devices based on MEH-PPV show higher Voc (as high as 1 V), while the application of P3HT results in lower Voc, but higher J sc and longer device stability. These observations have been associated to (a), the crystalline structure of TiO 2 and (b) to the form the polymer is bonded to the TiO 2 surface. In-situ IPCE analyses of P3HT-based solar cells show a red shift on the peak corresponding to TiO 2, which is not present on the MEH-PPV-based solar cells. The latter suggest that P3HT can be linked to the TiO 2 though the S-end atom, which results in devices with lower Voc. All these observations are also valid for devices, where the bare TiO 2 is replaced by an Nb–TiO 2. The application of an Nb–TiO 2 with rutile structure in these polymer/oxide solar cells is the reason for their higher stability under inert atmospheres. We conclude that the application of TiO 2 in its rutile phase is beneficial for long-term stability devices. Moreover there is an interplay between low Voc and J sc in devices applying P3HT, since power conversion efficiency can be partially canceled by their lower Voc in comparison with MEH-PPV. These findings are important for polymer/oxide solar cells, but also for organic solar cells, where a layer of semiconductor oxides are in direct contact with a polymer, like in an inverted or tandem organic solar cells.

Current distribution in HTSC tapes obtained by inverse problem calculation

The development of SC devices based on HTSC tapes requires a deep knowledge of the current distribution in both pre-saturation and post-saturation regimes. Magnetic measurements have shown the possibilities to derive the current distribution by Inverse Problem Solution in finite sized bulks, based on a non destructive measurement of the magnetic field created by the own current flowing in the SC. In this work, the QR inversion strategy is extended to non finite systems by considering the effect of the boundaries. We present a method to derive the current distribution in a cross-section of a tape based on Hall magnetic mapping by using a specifically designed inverse problem solver. This method is applied to a series of Hall measurements corresponding to a full magnetization cycle of a commercial tape, produced by applying a set of the currents applied to the tape of several intensities. Details of the experiments and the calculation method are reported and the applicability as homogeneity test and losses studies is discussed.

Characterization of Global Inversion Layer in Thin-Gate-Oxide Deep-Submicron p-MOSFETs

A simple electrical method is presented for the characterization of the inversion layer in p-channel MOSFET's with either p + poly gate (surface-channel, SC) or n + poly gate (buried-channel, BC). The dc centroid of the inversion layer profile, X c, represents the effective thickness of the inversion layer in the SC device or the physical location of the buried-channel in the BC device. For the first time, it is well demonstrated that, based on the small-signal gate-to-channel capacitance measurement, the global inversion layer hole profiles in both types of p-MOSFET's can be constructed from three elements, i.e., X c (dc centroid), X w (band diagram characteristic width) and Δ N inv (increment of net carrier area density).

Electrical characterization of inversion layer carrier profile in deep-submicron p-MOSFETs

A simple electrical method is presented for the characterization of the inversion layer in p-channel MOSFETs with either poly gate (surface channel, SC) or poly gate (buried channel, BC). The d.c. centroid of the inversion layer profile, , represents the effective thickness of the inversion layer in the SC device or the physical location of the buried channel in the BC device. For the first time, it is well demonstrated that, based on the small-signal gate-to-channel capacitance measurement, the global inversion layer hole profiles in both types of p-MOSFETs can be constructed from three elements, i.e. (d.c. centroid), (band diagram characteristic width) and (increment of net carrier area density).

Dynamic-RAM fabrication poised for continuing C-H-MOS invasion : Ken Yu, Ron Chwang and Amr Mohsen. Electronics 121 (5 April, 1984)

A simple electrical method is presented for the characterization of the inversion layer in p-channel MOSFET's with either p+ poly gate (surface-channel, SC) or n+ poly gate (buried-channel, BC). The dc centroid of the inversion layer profile, Xc, represents the effective thickness of the inversion layer in the SC device or the physical location of the buried-channel in the BC device. For the first time, it is well demonstrated that, based on the small-signal gate-to-channel capacitance measurement, the global inversion layer hole profiles in both types of p-MOSFET's can be constructed from three elements, i.e., Xc (dc centroid), Xw (band diagram characteristic width) and ΔNinv (increment of net carrier area density).