Rajaram S. Mane

Chemical deposition method for metal chalcogenide thin films

Abstract Metal chalcogenide thin films preparation by chemical methods are currently attracting considerable attention as it is relatively inexpensive, simple and convenient for large area deposition. A variety of substrates such as insulators, semiconductors or metals can be used since these are low temperature processes which avoid oxidation and corrosion of substrate. These are slow processes which facilitates better orientation of crystallites with improved grain structure. Depending upon deposition conditions, film growth can take place by ion-by-ion condensation of the materials on the substrates or by adsorption of colloidal particles from the solution on the substrate. Using these methods, thin films of group II–VI, V–VI, III–VI etc. have been deposited. Solar selective coatings, solar control, photoconductors, solid state and photoelectrochemical solar cells, optical imaging, hologram recording, optical mass memories etc. are some of the applications of metal chalcogenide films. In the present review article, we have described in detail, chemical bath deposition method of metal chalcogenide thin films, it is capable of yielding good quality thin films. Their preparative parameters, structural, optical, electrical properties etc. are described. Theoretical background necessary for the chemical deposition of thin films is also discussed.

Achievement of 4.51% conversion efficiency using ZnO recombination barrier layer in TiO2 based dye-sensitized solar cells

The authors report the use of chemically deposited ZnO recombination barrier layer for improved efficiency of TiO2 based dye-sensitized solar cells. The ZnO layers of different thicknesses were deposited on spin coated porous TiO2. The presence of ZnO over TiO2 was confirmed by x-ray diffraction, electron dispersive x-ray analysis, and supported by x-ray photoelectron spectroscopy, proved inherent energy barrier between the porous TiO2 electrode and lithium iodide electrolyte. They found that TiO2 based dye-sensitized solar cell with 30nm ZnO layer thickness showed 4.51% efficiency due to the formation of efficient recombination barrier at electrode/electrolyte interface. Further increase in ZnO barrier thickness may leak the electrons injected from the dye due to its low electron effective mass of 0.2me.

Deposition of CdS thin films by the successive ionic layer adsorption and reaction (SILAR) method

Abstract CdS thin films were prepared by the successive ionic layer adsorption and reaction (SILAR) method. The structural, optical, and electrical characterizations were carried out using X-ray diffraction, scanning electron microscopy, optical absorption, and electrical resistivity methods. The CdS films were annealed at various temperatures (373–673 K) in nitrogen atmosphere for 30 min and their structural, optical, and electrical properties are reported.

Studies on chemically deposited cadmium sulphoselenide (CdSSe) films

Thin films of cadmium sulphoselenide (CdSSe) have been chemically deposited using cadmium salt, thiourea and sodium selenosulphate, covering total composition range from CdS to CdSe. The structural, optical and electrical properties of these films have been studied. It has been found that CdS films are cubic, while mixed (CdSSe) and CdSe films are hexagonal. The optical absorption studies showed that as Se content in CdS film increases, bandgap, Eg decreases from 2.5 eV (CdS) to 1.8 eV (CdSe). The electrical resistivity of CdS is higher than that of mixed and CdSe films.

Successive ionic layer adsorption and reaction (SILAR) method for the deposition of large area (∼10 cm2) tin disulfide (SnS2) thin films

Simple and versatile, the successive ionic layer adsorption and reaction (SILAR) method was used to prepare large area (∼10 cm2) SnS2 thin films of about 1.0 μm thickness, under optimized deposition conditions. The films were grown on amorphous glass and single crystal wafer of Si(111) to study the effect of substrate on the microstructure of the films. The SnS2 films on glass substrate were amorphous or consisted of fine grains, while nanocrystalline grain growth was observed in filmes on single crystalline Si(111) substrate. The surface morphology of SnS2 film on the glass substrate looked relatively smooth and homogeneous in the scanning electron microscopy (SEM) image. The SnS2 film exhibited n-type electrical conductivity, and had an optical bandgap of 2.6 eV. The room temperature electrical resistivity was of the order of 103 Ω-cm.

Facile synthesis of manganese carbonate quantum dots/Ni(HCO3)2–MnCO3 composites as advanced cathode materials for high energy density asymmetric supercapacitors

We have developed a high performance supercapacitor cathode electrode composed of well dispersed MnCO3 quantum dots (QDs, ∼1.2 nm) decorated on nickel hydrogen carbonate–manganese carbonate (Ni(HCO3)2–MnCO3) hedgehog-like shell@needle (MnCO3 QDs/NiH–Mn–CO3) composites directly grown onto a 3D macro-porous nickel foam as a binder-free supercapacitor electrode by a facile and scalable hydrothermal method. The MnCO3 QDs/NiH–Mn–CO3 composite electrode exhibited a remarkable maximum specific capacitance of 2641.3 F g−1 at 3 A g−1 and 1493.3 F g−1 at 15 A g−1. Moreover, the asymmetric supercapacitor with MnCO3 QDs/NiH–Mn–CO3 composites as the positive electrode and graphene as the negative electrode showed an energy density of 58.1 W h kg−1 at a power density of 900 W kg−1 as well as excellent cycling stability with 91.3% retention after 10 000 cycles, which exceeded the energy densities of most previously reported nickel or manganese oxide/hydroxide-based asymmetric supercapacitors. The ultrahigh capacitive performance is attributed to the presence of the high surface area core–shell nanostructure, the well dispersed MnCO3 quantum dots, and the high conductivity of MnCO3 quantum dots as well as the synergetic effect between multiple transition metal ions. The superior supercapacitive performance of the MnCO3 QDs/NiH–Mn–CO3 composites makes them promising cathode materials for high energy density asymmetric supercapacitors.

Preparation and characterization of Bi2Se3 thin films deposited by successive ionic layer adsorption and reaction (SILAR) method

A successive ionic layer adsorption and reaction (SILAR) method which is a simple and versatile for yielding good quality Bi2Se3 films of thickness upto1.2 mm under a choice of deposition conditions is presented. The films were deposited onto glass and single crystalline wafer of Si(1 1 1). The structural, optical and electrical properties were studied. The thin films were smooth and homogeneous. The films annealed at 473 K in air for 1 h, did not show significant change in crystallinity and optical bandgap. # 2000 Elsevier Science S.A. All rights reserved.

Nanocrystalline CdS-water-soluble conjugated-polymers: High performance photoelectrochemical cells

Enhanced photoelectrochemical cell performance of nanocrystalline CdS-water-soluble conjugated-polymer sensitizers was demonstrated. The water-soluble polymers with quaternary pyridinium salts can be easily layered after dipping nanocrystalline CdS films in the aqueous polymer solution. The 2.37% energy conversion efficiency of CdS-poly(2-ethynyl-N-carboxypropylpyridiniumbromide) (LM 3) conjugated-polymer sensitizer was significantly higher than that of the bare (0.57%) and CdS-poly(2-ethynyl-N-aminopropylpyridiniumbromide) (LM 2) conjugated-polymer sensitizer (2.15%) under AM1.5 condition (80mW∕cm2).

Simple and low-temperature polyaniline-based flexible ammonia sensor: a step towards laboratory synthesis to economical device design

Flexible and highly sensitive polyaniline-based (PAni) ammonia (NH3) gas sensors were developed through in-situ chemical oxidative polymerization of aniline on a polyethylene terephthalate substrate at three different temperatures, viz. 35 °C, 0 °C and −5 °C. In the initial stage, they were characterized with respect to their structural, morphological, and compositional analysis studies and in the second stage, the selectivity towards oxidizing (nitrogen dioxide, NO2) and reducing (NH3, ethanol, methanol and hydrogen sulphide, H2S) gases was tested. The sensor fabricated at 0 °C showed an optimum response of 26% to 100 ppm NH3 gas, which was superior to those obtained for the sensors developed at 35 °C (19%) and −5 °C (23%). The as-developed low-temperature flexible gas sensor demonstrated fast response (19 s) as well as recovery time (36 s) periods, 99% reproducibility and good stability, revealing commercial application potential for example in industry where high temperature operation is prohibited. Impedance spectroscopy was used to investigate the plausible interaction mechanism of the NH3 gas molecules with the flexible PAni. The operation of the NH3 gas sensor device, fabricated on a laboratory scale, was tested and explored as a demo-video clip.

Hydrogel-Assisted Polyaniline Microfiber as Controllable Electrochemical Actuatable Supercapacitor

Flexible, controllable, and stable electrochemical supercapacitors serving as actuators at low operating voltage combining the advantages of the high power of the dielectric capacitors and the high specific energy of rechargeable batteries are important in artificial muscle technology, hybrid electric vehicles, and in short-term power sources for mobile electronic devices [Baughman, Science, 300, 268 (2003); Winter and Brodd, Chem. Rev. (Washington, D.C.), 104, 4245 (2004); Ebron, et al., Science, 311, 1580 (2006)]. High capacitance, a surprising 99% inner charge contribution and actuation in the hydrogel-assisted actuatable electrochemical supercapacitor (HAES) microfiber fabricated through wet spinning of a chitosan solution, followed by the in situ chemical polymerization of aniline was made possible through the perfect utilization of the large surface area provided by the nanostructured polyaniline grown inside as well as on the surface of the fiber. The HAES electrodes with an actuation strain of 0.33% showed 703 F/g specific capacitance in 1 M methane sulfonic acid, and more than 3000 cycles durability. The change in impedance as well as capacitance was achieved by the controlled strain as a function of applied stress, which can establish a direct relationship between the actuation strain and specific capacitance of electrochemical supercapacitors.