Materials Science Forum Vol. 832

Abstract: CdSe and its Zn/In/suitable element doped films are very important interesting materials for the realization of electronic and photoelectronic devices for energy conversion. The growth of ternary In/Zn/Cd selenides opens up the possibility of their applications for novel opto-electronic devices in the visible region of electromagnetic radiation. The (CdZn)Se and (CdIn)Se systems enable a tunable band gap region between 1.72 and 2.82 eV at normal temperature facilitating the development of several new light emitting diodes, photo detectors, blue green lasers. Thin films of these materials are usually synthesized by molecular beam epitaxy, electron beam evaporation and chemical techniques. Many researchers have reported about these materials prepared by different techniques and their properties as well as their use in PEC cell fabrication mainly followed by other optoelectronic devices also. This review gives an account of all these data in a representative distributed manner so as to cover many decades of published papers in this ever green topic of energy conversion research.

Abstract: Recently, numerous delafossite oxides in nanoscale have been reported for diverse applications. The present review summarized the recent overall views of delafossite nanoparticles in diverse applications such as energy, catalysis, photocatalysis, nanomedicine, sensors, electrochemical devices and environmental concerns. Delafossite nanoparticles possess unique features such as different and wide chemical composition, large surface area, small energy gap, ability for further functionalization, possess dual-active sites with different oxidation states (A⁺ and M³⁺), and eager for doping with various species with feasibility to undergo structure modification. Thus, they provided promising application such as solar cell, photocatalysis, hydrogen production, bioactive materials, separation purposes and others. Pros, cons, current and future status were also reviewed.

Abstract: A theoretical explanation of optics behind TiO₂ has been presented with the help of a four phase model air/glass/ indium doped tin oxide/TiO₂ designed by modifying Rouard’s model to calculate the final transmittance in to TiO₂ layer. An optical simulation for the reflectance and transmittance has been executed for the synthesized nanocrystalline TiO₂ films. To validate the theoretical results TiO₂ film has been deposited onto indium doped tin oxide (ITO) layer by sol-gel dip coating technique. The novelty of the task lies behind the fact that transmittance helps to calculate the light harvesting efficiency of the Dye-Sensitized solar cells which is the ratio of light actually harvested to the light actually reached to TiO₂ layer, and that can be done only if one knows transmittance.

Abstract: A low-cost platinum (Pt) free electrocatalyst of NiSe₂ and Ni_0.9X_0.1Se₂ (X=Cd, Co, Sn and Zn) have been developed by hydrothermal reduction route and utilized as counter electrode (CE) in dye-sensitized solar cells (DSSCs). The purity, phase formation and morphology of the sample were characterized by X-ray diffraction, field-emission scanning electron microscopy and energy dispersive spectroscopy. The electrocatalytic activity of the synthesized selenides for the reduction of I₃^- to I^- was evaluated using cyclic voltammetry and electrochemical impedance spectroscopy. The Ni_0.9Zn_0.1Se₂ CE exhibited lower internal resistance and higher electrocatalytic activity than the other ternary metal selenides and this may be due to an increase in the electrocatalytic active sites on the surface of Ni_0.9Zn_0.1Se₂. As a result, the DSSC fabricated with Ni_0.9Sn_0.1Se₂ CE achieved a high power conversion efficiency of 4.20% under an illumination of 100 mW/cm², which is comparable to that of DSSC with Pt CE (6.11%). These results demonstrate the potential application of Ni_0.9Zn_0.1Se₂ as an alternative CE to replace expensive Pt in DSSCs. This study can be further extended for the development of new metal selenides based CE electrocatalysts with high activity for the DSSCs.

Abstract: Influence of hematite iron oxide nanoparticles (α-Fe₂O₃ NPs) on ionic conductivity of polyvinyl alcohol/KI/I₂ (PVA/KI/I₂) polymer electrolytes was investigated in this work. The pure and different weight percentage (wt %) ratios (2, 3, 4 and 5 % with respect to PVA) of α-Fe₂O₃ NPs incorporated PVA/KI/I₂ polymer electrolyte films were prepared by solution casting method using DMSO as solvent. The prepared polymer electrolyte films were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffractometer (XRD) and alternating current (AC)-impedance analysis. The AC-impedance studies revealed a significant increase in the ionic conductivity of α-Fe₂O₃ NPs incorporated PVA/KI/I₂ polymer electrolytes than compared to pure PVA/KI/I₂. This incorporated polymer electrolytes reduces the crystallinity of the polymer and enhance the mobility of I^-/I₃^- redox couple, thereby increasing the ionic conductivity of polymer electrolytes. The highest ionic conductivity of 1.167 × 10^-4 Scm^-1 was observed for 4 wt % of α-Fe₂O₃ NPs incorporated PVA/KI/I₂ polymer electrolyte. Also, the dye sensitized solar cell (DSSC) fabricated with this electrolyte showed an enhanced power conversion efficiency of 3.62 % than that of pure PVA/KI/I₂ electrolyte (1.51 %). Thus, the synthesized α-Fe₂O₃ NPs added polymer electrolyte can be serve as a suitable material for dye sensitized solar cell application studies.

Abstract: CdSe thin films doped with 10% of Indium and 10 % Zinc were prepared by electron beam evaporation technique and the films were annealed at 200 oC for 30 min. Well crystalline films were deposited and the crystallite variation was studied for doping effect and it was found to be about 48 and 52 nm respectively. Optical band gap values are found to be modified by doping as well as annealing. PEC solar cells were fabricated using CdSe:In and CdSe:Zn films which showed 1.54% and 1.88% conversion efficiency respectively. Annealed films showed considerable influence in the optoelctronic properties and its improvement in conversion efficiency to about 2.75% and 2.87% respectively. In order to increase the photo output the films were annealed at 200o C at temperature. The photo output was Voc = 0.476 V, Jsc = 9.8 mA cm^-2, ff = 0.44, η = 2.76 % at 80 mW cm^-2 . Photoetching increased the output parameters.

Abstract: Crystalline SnO₂ – TiO₂ thin films were deposited on glass substrates by using the precursor solution containing tin acetate and calcium titanate as the source materials. After the deposition, the films were subjected to annealing at two different temperatures of 150o C and 300⁰ C. The structural, morphological and electrical properties have been investigated. X-ray diffraction analysis showed that the as-deposited as well as the annealed films were well crystallized and polycrystalline with cubic structure having (110) preferred orientation. AFM analysis showed uniform surface morphology with very low surface roughness values. The electrical parameters like the resistivity values are found decreasing and the mobility and carrier concentration values are observed to increase with annealing temperature. Sensor studies on SnO₂ – TiO₂ films annealed at 300^o C showed very good response to methanol gas.

Abstract: High quality micro sheet rhombohedral graphite crystals were synthesized by Hummer method using compounds of MWCNT, K₂S₂O₈ and P₂O₅. The growth mechanisms were discussed by finite element simulation. The synthetic sheet rhombohedral graphite crystals showed a higher growth rate in radial direction than that in axial direction. Raman spectrum and Fourier transform infrared spectrum indicated that synthesized sheet rhombohedral Graphite had fewer crystal lattice distortions with no impurities. Finite element simulations indicated that the solvent metal convection field in the radial direction was stronger than that in the axial direction. As prepared graphite powder was annealed at 1350 oC to obtain diamond nanoparticles. The as-prepared products were exposed to formaldehyde gas.

Abstract: In this work, Ni and SnO₂ loaded Chitosan nanomaterials are prepared by neutralization method, obtained by drop wise addition of Chitosan solution to a solution of NaOH, followed by cross-linking. The Structural, morphological and Raman analyses are carried out. The antibacterial activity is analysed against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa and evaluated by the calculation of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The obtained results show that, Ni-loaded nanoparticles could inhibit the growth of various bacteria better than SnO₂. These results revealed that, the exposure of Staphylococcus aureus to the Chitosan nanoparticles led to the disruption of cell membranes and the leakage of cytoplasm.