Optimization of PbS thin films using different metal ion sources for photovoltaic applications

An extensive study on the influence of metal ion sources on the properties of chemical bath deposited lead sulphide thin films is reported in this paper. Four different lead sources namely lead nitrate, lead acetate, lead chloride and lead sulphate in alkaline medium have been used for the synthesis along with thiourea as sulphur source. The influence of lead sources on structural, surface morphological optical and electrical properties is investigated for photovoltaic applications. According to X-ray diffraction studies, all the films are poly crystalline with face centered cubic structure. The average crystallite sizes are found to be in the range 13–24 nm. The SEM photographs showed diverse morphology. The optical band gap is found to be very sensitive to the metal sources used. The direct band gap energy values obtained are in the range of 1.862–2.609 eV. The electrical conductivity varies in the range 33.6 ?7.62 × 10^?9 (Ω cm)^?1. Photosensitivity is closely linked to surface morphology. In this work, we established that the cationic precursor sources have significant role in physical properties of as-deposited PbS thin films. Samples prepared using nitrate as metal source are found to be most suitable to be used as solar control coating and the samples with lead acetate can be used as absorber layers for solar cell fabrication.     

Evaluation of termiticidal activity of coconut shell oil and its comparison to commercial wood preservatives

Among several factors leading to biodegradation of wood, termites are one of the most damaging agents to wooden structures worldwide. To avoid environmental pollution and health problems caused by the use of synthetic pesticides, wood preservation research is currently focusing on discovery and application of termiticides derived from plants. This paper reports and discusses the use of coconut shell oil (CSO) as a potential termiticide. Termiticidal activity of CSO was assessed and compared to wood preservatives currently in use. After 18 months of field trial, all the control stakes were destroyed completely and there was damage of 34.2 % in the CSO brush coated stakes. CSO is a promising new biodegradable compound which can be utilized for the development of a termiticide of biological origin.     

Growth features of ammonium hydrogen<Emphasis Type="Italic">d</Emphasis>-tartrate single crystals

Ammonium hydrogend-tartrate (d-AHT) single crystals were grown in silica gel. The growth features of these crystals with variation of parameters like specific gravity of the gel, gel pH, acid concentrations, concentration of the feed solution and gel age were studied in detail.     

Electrical,thermal and microwave shielding properties of printable silver nanowires

Silver nanowires find use in a myriad of applications, including communication systems, sensors, medical devices and electrical equipment. Temperature-dependent electrical and thermal properties of chemically derived silver nanowires are rarely explored. In the present work, seed-mediated synthesis of silver nanowires has been carried out, and their electrical and thermal conductivity at 300 K is found to be 1.848?×?10⁷ S/m and 64.8 W/mK, respectively. A screen-printable ink of silver nanowires is formulated and printed on low-cost and widely used substrates like paper and cotton fabrics. Flexible printed electrodes could be made possible with uniform printed structures obtained in cotton fabric and paper substrate. The printed pattern exhibited sheet resistance of 0.7 Ω/sq. Screen-printed silver nanowires on paper show shielding efficiency of 99.9% in X band, which promotes them as excellent candidates in fabricating lightweight electronic devices by a one-step printing process.

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Effect of deposition time on optical and luminescence properties of ZnS thin films prepared by photo assisted chemical deposition technique

Photo assisted chemical deposition method (PCD) is a new procedure for the deposition of compound semiconducting materials which is less explored. In this method the deposition is carried out with the irradiation of UV light on the reaction bath. PCD scores advantages for its low cost, use of flexible substrates and capability of large area deposition compared to other chemical methods like chemical bath deposition (CBD), electro chemical deposition (ECD), etc. Zinc sulfide films have been deposited on glass substrate by aqueous alkaline solution comprised of zinc nitrate, hydrazine hydrate, ammonium nitrate, ammonia and thiourea. The samples were prepared under UV illumination for different durations and characterized. The thickness of the samples increases with the deposition time. XRD patterns revealed the crystalline nature of samples with more number of dips. Optical study showed a low absorbance and constant transparency throughout the visible region disclosing the stiochiometric nature of the film. Obtained band gap energies were in good agreement with the theoretical value. Photoluminescence spectra showed two blue emission bands around 450 and 470 nm, and the intensity was found to depend on the thickness of the films.     

Influence of ammonia, lithium hydroxide, and hexamine on ZnO films synthesized by successive ionic layer adsorption and reaction technique

Various nanostructured zinc oxide (ZnO) films have been developed on non-seeded soda-lime glass substrates by successive ionic layer adsorption and reaction (SILAR) method, employing different baths of aqueous zinc sulfate solution using complexing agents of ammonia, lithium hydroxide, and hexamine. Influence of complexing agents on the structural, morphological, chemical compositional, optical and electrical properties of the films were investigated and compared among and with the samples annealed at 400 °C. Role of complexing agents on the growth process was discussed. X-ray diffraction analysis revealed that the ZnO films were polycrystalline dominating with (100), (002), and (101) oriented crystallites of hexagonal wurtzite structure. The lattice constants, c/a ratio, internal relaxation parameter, anion–cation (Zn–O) bond length, and the tetrahedral angles of ZnO films were determined. Cauliflower, flower, and flower-like nanorod morphologies of the films from the respective baths were exposed by scanning electron microscopic studies. Optical analysis of all films except that prepared from hexamine showed low absorbance and a higher transmittance 70–85 % in the entire visible region. Resistivity of annealed films was one order of magnitude lower than that of the as-grown films. We demonstrated utility of SILAR as an efficient single step soft chemical route for obtaining high-quality crystalline ZnO films having high-specific surface area on non-seeded substrates.     

Investigations on the Structure,Morphology, and Optoelectronic Properties of Chemically Deposited ZnSe Thin Films: The Effect of Solution pH

Nanocrystalline ZnSe films were prepared by the chemical bath deposition technique by varying the pH of the reaction bath from 9.2 to 10.6, and the physical properties of the annealed films were investigated. The x-ray diffraction profiles of the samples showed hexagonal structure of ZnSe nanocrystallites except for films deposited at pH 10.6. Strain was compressive, but became tensile with increase in pH. Topographical studies by atomic force microscopy showed a smooth surface of the samples deposited at higher pH and therefore low surface roughness. Optical studies revealed homogeneous grain shape and size. The thickness, grain size, and bandgap of the samples showed consistent results. The photoluminescence emission peaks occurred at the same wavelength for different pH values. The physical properties of the annealed samples seem to make them suitable for application as buffer layers in thin-film solar cells.     

Enhanced excitonic emission and visible luminescence of chemically synthesized ZnS:Co film phosphors

Undoped and Cobalt doped ZnS thin films have been synthesised using chemical bath deposition technique. The X-ray diffraction pattern revealed a hexagonal structure for all the films. An increase in Co/Zn molar ratio resulted in a decrease in the intensity of diffraction peak corresponding to (100) plane and increase in crystallite size of the samples. The transmittance of the samples in the visible region was found to improve on doping. The optical band gap was found to vary from 3.46 to 3.66 eV with the incorporation of cobalt ions. The scanning electron microscope images of the samples exhibit a denser and more compact morphology for the doped films as compared to the undoped film. Photoluminescence studies reveal that all samples exhibit rare excitonic or near band-edge luminescence along with emissions in the visible region. The luminescence efficiency of ZnS film is appreciably enhanced with increase in concentration of the dopant.     

Band gap engineering in PbSe thin films from near-infrared to visible region by photochemical deposition method

Lead selenide (PbSe) thin films have been synthesized by the established photochemical deposition technique using lead nitrate and lead acetate as sources for the metal ions and sodium seleno sulphate as the selenium source along with triethanolamine, ammonia and hydrazine hydrate as complexing agents. A comprehensive study of the effect of substrate materials on physical properties of as deposited PbSe thin films is reported in this work. Two substrates were used in this investigation, namely soda lime glass slides and gold coin corning glass slides. The solution is irradiated with UV light and the photochemical reactions in the aqueous solution resulted in highly adherent metallic thin films. X-ray diffraction (XRD), scanning electron microscopy, optical and electrical measurement techniques were used for film characterization. The XRD analysis confirmed that all films were cubic, regardless of the cationic precursors and substrates used. The scanning electron microscope micrographs showed variations in morphology. The optical studies revealed that the films have good absorption in the visible region. The remarkable success of our effort was that we have been able to modify optical band gap of PbSe thin films over a wide spectral range by a cost effective route. The band gaps estimated from the transmission spectra were in the range 1.32–1.40 eV for films deposited on soda lime glass substrates and 1.46–1.55 eV for corning glass substrates. The room temperature conductivity of the PbSe films were in the range of 3.71 × 10^?7–513 × 10^?7 (Ω cm)^?1. The as deposited PbSe thin films with low transmittance in the visible region coupled with an appreciable reflectance in infrared region were found to satisfy the basic requirements for solar control coatings for window glazing applications in warm climates. Through this work we established that irrespective of metal salts, soda lime glass substrate was superior to corning glass substrate.     

Effect of processing on the retention of carotenoids in yellow‐fleshed cassava (Manihot esculenta Crantz) roots

The retention of carotenoids was studied in roots from yellow‐fleshed, high carotene cassava clones in four different processing methods. The results indicated that the extent of retention varied with the method of processing. The highest retention was observed in oven drying (total carotenoids 54.70–84.01% and β‐carotene 63.90–94.53%) followed by boiling (total carotenoids 47.87–83.79% and β‐carotene 51.31–81.04%) and frying (total carotenoids 48.76–79.77% and β‐carotene 44.11–83.87%). The lowest retention of total carotenoids (32.86–56.40%) and β‐carotene (21.47–56.68%) was recorded in the sun drying method. The variation in the total carotenoids and β‐carotene content depends on variety, processing method and initial carotene content of the fresh root.