Solution-processed CuZn1−xAlxS2 : a new memory material with tuneable electrical bistability

CuZn1−xAlxS2 (CZAS) thin films deposited by the chemical spray pyrolysis (CSP) technique exhibit reversible electrical bistability in current–voltage measurements. The threshold voltage and current for switching can be tuned by the initial voltage applied to reset the device. X-ray diffraction and high-resolution transmission electron microscopy imaging show that the initial crystal structure of CZAS is similar to CuAlS2 with slightly expanded lattices due to the presence of Zn. The electrical memory effect in this material is observed only when both Zn and Al are present in the film, indicating that migration of interstitial Al towards the anode may be the origin of this memory effect

Electrodeposition of single phase CuInSe2 for solar energy harvesting : role of different acidic additives

Single phase CuInSe2 (CIS) absorber material is required for producing high quality thin film solar cells, as the presence of impurity Cu2−xSe leads to short circuit of the cells. Traditionally, the deposition of single phase CIS requires the use of a suitable chelating agent to shift the Cu2+/Cu redox couple towards the redox potential of the In3+/In couple, and also an acid to adjust the pH of deposition bath around 2. We propose a novel idea of using suitable acids that could concurrently also serve as the chelating agent. Oxalic acid, acetic acid and hydrochloric acid were investigated on their ability to serve this dual function. We found that oxalic acid is the most promising additive because the CIS film deposited was densest and yielded the highest photocurrent.Accepted versio

Manganese-doped polyaniline electrodes as high-performance supercapacitors with superior energy density and prolonged shelf life

The rising energy ultimatum has urged a paradigm shift from conventional to non-conventional, green, and clean energy sources to indulge supply and demand. In light of this, manganese-doped polyaniline was synthesized via the In-situ oxidative polymerization method and was employed as material for supercapacitor electrodes. The doping of PANI by manganese was confirmed from EDX and XPS analysis. Electrochemical studies uncovered an areal capacitance of 776 mF/cm2 at a current density of 1 mA/cm2, gravimetric capacitance of 995 F/g at 1 A/g, 99% coulombic efficiency, and a capacitive retention of 86.5% was observed after 20,000 cycles at a current density of 35 mA/cm2 by the fabricated coin cell device. The shelf life performance of the coin cell was analyzed after 400 days and underwent a long run for one lakh cycles, which revealed a capacitive retention of 71% at 1 mA/cm2 and a stable coulombic efficiency of 96% throughout the cycling. From the performance analysis, the manganese-doped PANI claims to serve as an excellent electrode for supercapacitor applications

Metal/metal sulfide functionalized single-walled carbon nanotubes : FTO-free counter electrodes for dye sensitized solar cells

The use of single-walled carbon nanotubes (CNT) thin films to replace conventional fluorine-doped tin oxide (FTO) and both FTO and platinum (Pt) as the counter electrode in dye sensitized solar cells (DSSC) requires surface modification due to high sheet resistance and charge transfer resistance. In this paper, we report a simple, solution-based method of preparing FTO-free counter electrodes based on metal (Pt) or metal sulfide (Co8.4S8, Ni3S2) nanoparticles/CNT composite films to improve device performance. Based on electrochemical studies, the relative catalytic activity of the composite films was Pt > Co8.4S8 > Ni3S2. We achieved a maximum efficiency of 3.76% for the device with an FTO-free counter electrode (Pt/CNT). The device with an FTO- and Pt-free (CoS/CNT) counter electrode gives 3.13% efficiency

Enhancing the photocatalytic efficiency of TiO2 nanopowders for H2 production by using non-noble transition metal co-catalysts

Co and Ni-nanoclusters are attractive alternatives to Pt catalysts for hydrogen generation. These earth abundant elements when loaded onto the TiO2 nanopowders surface act as efficient co-catalysts. Co, Ni-decorated TiO2 photocatalysts display only three (3) times lower catalytic activities for H2 evolution under UV illumination compared with Pt-decorated TiO2 photocatalysts

Chemical welding of binary nanoparticles : room temperature sintering of CuSe and In2S3 nanoparticles for solution-processed CuInSxSe1−x solar cells

Chemical welding of oppositely charged dissimilar metal chalcogenide nanomaterials is reported to produce a quaternary metal chalcogenide. CuSe and In2S3 nanoparticles were synthesized with opposite surface charges by stabilizing with polyacrylic acid and polydiallyldimethylammonium chloride. Upon mixing these nanoparticles at room temperature, the electrostatic attraction induced coalescence of these nanoparticles and led to the formation of CuInSxSe1−x nanoparticles.Accepted versio

A ZnO nanowire resistive switch

An individual ZnO nanowire resistive switch is evaluated with Pt/ZnO nanowire/Pt topology. A detailed DC I-V curve analysis is performed to bring both the conduction mechanism and the device characteristics to light. The device is further studied at various vacuum pressures to ascertain the presence of polar charges in ZnO nanowires as the phenomenon leading to the formation of the switch. The disappearance of the resistive switching is also analyzed with two kinds of fabrication approaches Focused Ion/Electron Beam involved in the making the device and a summary of both length and fabrication dependences of resistive switching in the ZnO nanowire is presented.Published versio

A cuprous oxide–reduced graphene oxide (Cu2O–rGO) composite photocatalyst for hydrogen generation : employing rGO as an electron acceptor to enhance the photocatalytic activity and stability of Cu2O

Photocorrosion, that causes rapid deactivation of Cu2O photocatalysts, was addressed by incorporating this oxide in a composite with reduced graphene oxide which acts as an electron acceptor to extract photogenerated electrons from Cu2O. Cu2O–rGO composite engineering also allows enhancing significantly photocatalytic activities of Cu2O for H2 generation

Graphene oxide organogel electrolyte for quasi solid dye sensitized solar cells

Low concentration, as low as 0.4 wt.% graphene oxide organogels is reported for different organic solvents. The gelation of organic solvents at exceedingly low concentrations opens the door for the implementation of graphene oxides based electrolytes in various electrochemical applications. Here we demonstrate the use of acetonitrile–graphene oxide (GO) gel containing iodide/triiodide as a quasi-solid electrolyte for dye sensitized solar cells (DSCs). Electrochemical impedance studies reveal that the mass transfer barrier is not adversely affected by the presence of the minute amount of GO gel former. The achieved energy conversion efficiency (η) for the device without GO and with 1% GO gel electrolytes is 6.9% and 7.5% respectively under one sun illumination

Morphology and stoichiometry control of hierarchical CuInSe2/SnO2 nanostructures by directed electrochemical assembly for solar energy harvesting

CuInSe2/SnO2 core–shell and hierarchical branched nanostructures were produced by directed electrochemical assembly. By changing the spatial electric field along the deposition region, we can control the morphology and stoichiometry of deposited product from In-poor-CuInSe2 nanoparticles to near stoichiometry CuInSe2 branched nanowires. A combination of FESEM, TEM, XRD and Raman spectroscopy investigations reveals that both morphology and chemical compositions of CuInSe2 strongly depend on the spatial electric field distribution on the SnO2/Si substrate. We observed that higher reducing potential can assist the formation of CuInSe2 with uniform coverage at the cathode side, but only In-poor-CuInSe2 nanoparticles are formed on the anode side. Optical and photo-electrochemical examination confirmed the potential application of these core–shell nanostructures for solar energy harvesting